After purchasing my 1998 Ford Crown Victoria Police Interceptor, I decided to add a full featured alarm system that included keyless entry (with seperate lock & unlock buttons), starter kill and remote start.
Suppliers of intrest:
           
Individual sellers on www.ebay.com in the "Consumer Electronics:Car Audio & Electronics:Car Alarms" section. Many of the sellers are really businesses and use ebay solely as an advertising medium. For example running a dutch auction with a quantity of 55 new alarms forsale when the seller only resonably expects to sell 5 units. Such sellers often have feedback in excess of 1000 positive comments as well. If you choose this route do be aware that there are many used alarms forsale on ebay. Because of the amount of effort involved to install a remote car starter, it is recommended that you acquire a new unused alarm not a used one that has been previously removed from a customers vehicle.
store.autotoys.com has a very wide selection of alarms and alarm accessories, decent prices, good reputation, and company represenatives participate in the usenet group rec.audio.car from time to time.
www.partsexpress.com an electronics supplier, also sells car alarms, car amplifier wiring accessories, and has a good selection of items to build car subwoofer boxes.
www.mcmelectronics.com an electronics supplier that also sells remote start and car alarm related installation supplies
Door triggers -> At first, I had the BK/LB domelight power lead connected 
              to the positive trigger input of the alarm. But 1995+ crown 
vics     have     a  "theater  dimming" feature to the overhead domelight 
so that    it slowly     fades  off over  the course of a few seconds after 
a door  is  closed. Is   easier  on  the eyes  and looks neat too, but the 
feature  was  confusing the  alarm  in my car so I decided to tie directly 
to the door ajar switches instead.    Door ajar switches  are divided into 
two zones,   one zone has just the drivers    door on it, the  other has the
front passenger    and both rear doors on it.    I caught both the  driver's 
door ajar switch    and the passenger door switch    behind the drivers  side
kickpanel. Drivers    latch was dark blue in color,    passengers was black
 with an orange stripe.    Used two diodes to isolate  the  doors and tied
the combined input to the    negative trigger of the alarm.  
                             
If you've got an alarm that takes into account the theater dimming ramp 
              up and ramp down times, it may be easier to tie the domelight 
  wire     to   the    positive trigger input of your alarm than tap the two
  individual      door  ajar    switch wires. In civilian models, one can
tap  one of the   underdash     interior    lights that comes on when the
door  is opened. Most  police cars    do not have    these lights, in which
case  splice into the  BK/LB lead on   the LCM plug or   tap the lead that
runs  up to the headliner   mounted  domelight.
                              
Domelight supervision -> Can emulate one of the doors being opened by
grounding the dark blue wire (drivers door switch) or BK/O wire (front  passenger
& both rear door switches) on the LCM. Another method is to splice into
the BK/LB domelight lead at the back of the LCM.
                             
                             
Ticket Writing Light Supervision:
                             
The police ticket writing light is considerably brighter than the normal domelight, so i elected to use it for the domelight supervision feature of the alarm system. For this part of the project, I ran a new wire from the alarm control box/relay area up to the ticket writing light, spliced the wire in after the switch but before the lightbulb socket. Ticket writing light uses a switched ground and draws a large enough amount of current that use of a relay is required.
At first I was using the demand output as the sole positive power source for the domelight supervision of the police ticket writing light. Then started to have weird problems because of the battery saver feature of the LCM engaging. For instance, if the car had not been run in around 20 minutes, the police light would not come when the unlock button on the remote was pressed, but open the trunk and press the unlock button, and the police ticket writing light would come on for 30 seconds and shut off like it should when the ignition is turned to the on position.
Solved this problem by using a relay to selectively break the circuit that
wires the LCM demand lighting output to the police light, and apply 12volts
to police light LG/OG when domelight supervision is requested by alarm. Accomplished
this by cutting the LG/OG wire that runs to the light and spliced an SPDT
relay in and wired the common lead in to the side of the wire that runs to
the light, normally closed terminal to the side that runs to the LCM, normally
open terminal to a 12volt constant live wire. One side of the relay field
coil was tied to the constant hot black/white wire, and the other to the
pulsed ground output of the alarm.
                             
An alternative solution would have been to tie the domelight supervision 
              pulsed ground output to the trunk ajar switch located in the 
 latch.       This     would "wake up" the lcm and the demand lighting output 
 of the    lcm   would   become  live.
                              
Starter kill -> cut the W/PK located at the ignition switch, splice
               in your starter kill relay here. If installing a remote start
   setup,       apply     power to the starter motor side of the wire when
 you  want to   crank   the  engine.  A note about starter kill relays, tie
 one  of the coil   wires   and one of the  contact inputs to the side of
the starter  wire that   connects   to the ignition  switch output, tie the
other coil  wire to the   ground while   armed output of  the alarm, connect
the remaining    contact  to the side of  the starter wire that  runs to
the starter motor.    This extends   starter kill  relay life since the 
relay is only engaged   when the alarm  is armed AND the  key is turned to
the  start position.
                             
If one of the relay coil wires were tied to a constant +12V source and the other to the ground while armed output of the alarm, the relay would be powered 100% of the time when the alarm was armed. This would significantly decrease the lifespan of the relay, and would also cause a continuous ~200ma whenever the car was parked and the alarm was armed. Leave the car parked for a couple weeks in the cold weather with the alarm armed and you may not have enough power left in the battery to start it when you get back from your vacation.
Hood switch -> police models have a light that turns on when hood is opened, this is accomplished by using a mercury switch to determine when hood is open or not. For accuracy's sake, install an aftermarket pin switch if you want your alarm to be able to sense when the hood is open. Can skip hood switch install, but if you want remote start setup installed, a hood pin switch is highly recommended so the car will not accidentally remote start during engine service (hood open).
Trunk ajar switch -> All 1995 and later crown vics will have three wires connecting to the trunk latch. To sense when the trunk is open, tap the BR/W wire at the LCM and connect it to a negative trigger input of your alarm module. The BR/W wire provides a ground path whenever the switch built into the latch senses that the latch is in the unlatched position. There is also a mercury switch located drivers side hinge on the underside of the trunklid. The mercury switch receives power from the demand lighting output of the lcm and the output terminal of the mercury switch is wired in series with the trunk light. The P/Y (Purple with yellow stripe) wire has a momentary +12V pulse on it when the trunk release button is pressed. The black wire is on the latch is ground.
Horn -> The horn button on the steering wheel does not drive the horn
            directly. Instead the control switch sends a ground pulse to
the    horn     relay    located under the hood which in turn sends power
to the    pair of   horns located    on the front frame rails. To energize
the horn    send a low   current ground   pulse to the DB (dark blue) wire
located at   the base of  the base of the steering   column. My 98' p71 also
had the DB  horn control  wire present on one of the   LCM connectors, but
the horn wire  on the LCM  is mainly for the panic button   on the civilian
vic factory  remote keyless  entry system and may not be present   on some
police interceptors.
                        
Key in ignition lock sense -> The ignition lock cylinder provides a
            ground path through the black/pink while the key is in the ignition,
       and    can be tapped either at the base of the steering column or
at   the    LCM. 
                        
An interesting side point, the ignition warning buzzer is located inside
            the LCM. Even if you cut the key sense wire, you will still get
  a  warning        tone if you have the ignition key turned counter-clockwise
    to the accessory        position and open the drivers door. However you
  won't  recieve a warning      tone  if the key is in the off position and
  the door  is ajar.
                         
Without keyless entry (i.e. interceptors and base model vics) -> Reverse
               polarity, ground at rest setup. Lock actuator solenoids are
 wired      in   series     through the drivers and passengers power lock
switches.    Both   terminals    of  the lock actuators are grounded at rest,
when switch    is  pressed to lock    doors,  a positive 12volts is applied
to one wire   of the  lock acuator,  the   other wire is held at ground.
Reversing polarity     on the lock acuator  (swapping   which  terminal is
grounded and which  one   is hot) will unlock  the door instead   of  lock
it. The PK/Y and PK/LG   wires  run from the drivers  door to the passengers
  door and then to the   lock acuators. The easiest place to catch them is
behind   the glovebox above  the passenger's side kickpanel.   If the alarm
you choose   does not have  onboard door lock relays, you'll  need two SPDT
relays to interface   your  alarm with the power door locks.
                           
Is no "plug and play" way to connect a keyless entry system into a crown 
             vic that is not equipped with the factory keyless entry system, 
   so   you're       going to have to "cut and splice" if you want this feature. 
     (C515 is  located     in the middle of the drivers door). Ford has been 
   using  the same  basic  design   and wire color coding scheme for it's 
power   lock  system for  crown  vics since   the 1970's. If you've got an 
older  vic, you  will not have the  switch illumination   leds or the connection 
  to the lighting    control  module  but the rest of the   power lock system 
  should be essentially    remain  the same.
                           
To splice the relays into your crown vic, cut at the PK/Y and PK/LG wires 
             at the locations marked by the blue and red X's. This will leave 
    you    with     four exposed wire ends. Tie Pin 30 (common) of the relay 
   to the   side of   the  power lock relay that runs to the passengers side 
   door, tie   pin 87a  (normally  closed) to the side of the wire that runs 
   to the drivers   door.  Strip some  insulation off the constant live BK/W 
   wire and connect   it to each of the 87 (normally open) contacts and 85 
 (coil  wire) of each  relay. Now put another  wire on the remaining 86 terminal 
  of each relay and  momentarily  touch it to ground. Touching pin 86 of one
  relay to ground should  unlock all the doors,  touching the other relay's 
  pin 86 to ground should  lock the doors. If the  fuse blows when you touch 
  pin 86 to ground, reverse  the connections  of pin   30 and 87a, install 
 a new fuse and try again.
                           
Now check the drivers door lock switches to make sure that the doors lock 
             when the powerlock switch is pressed to the lock position and 
 they     unlock       when it is pressed to the unlock position. If the door
 locks     do not function      at all, the relays or your splices into the
 vehicle    harness are not connected      properly. Aditionally, make sure
 that the   doors do not lock when the drivers     door switch is pressed 
to the unlock   position.
                           
                           
                           
                           
                           
                           
With keyless entry (i.e. crown vic LX with keyless entry keypad on drivers door) -> Positive trigger. Apply 12 volts to the PK/Y wire when you want the door to lock, and apply 12volts to the PK/LG when you want the door to unlock. Negligible current draw, but unless your alarm has positive trigger outputs for the door locks, you will still need two relays for the negative trigger alarm lock/unlock outputs. Can grab wires at similar places as the nonkeyless entry vics mentioned in previous paragraph.
Note that 92'-94' crown vics use a negative trigger lock system, not a 
             positive trigger one.
                           
                           
                        
                        Power Trunk Release-> Crown vics without the factory 
   keyless     entry    system   have a momentary switch with one side wired 
   to a constant     live  and  the other   wired directly to the trunk pop 
  actuator. On crown     vics with the factory  keyless entry system, the 
trunk  switch is just an   input to the drivers door  module which requests 
the the trunk pop actuator    to be engaged. Wiring an  aftermarket keyless 
entry  system to engage the   trunk pop actuator is the same on both vehicles, 
send  a +12V pulse to the   side of the P/Y (purple  with yellow stripe) 
wire that feeds the actuator.   Can access the needed wire either behind the
 drivers side kickpanel or in  the bundle of wires above the drivers side
rocker  panel under the scuff  plate.
                            
Spark plug sense -> 1998 and later crown vics do not have a dedicated
               tach output signal, can use one of the pcm leads to the COP
 assemblies           on  98's but they may be too noisy for some older remote
 starts due    to   multiple firing of each ignition coil during the combustion
 stroke   at  low   idle speeds.
                  
Using voltage sense as the sole method of determining when the car is running sounds good in theory. Alternator does not generate any power when car is not running, and battery voltage will jump up when car is running. But using voltage sense is troublesome when actually implemented as sole method of monitoring when car is running and when it is not. Alternatively you can use a vacuum switch instead. For 97's and prior, run a new lead from pin48 on the PCM to your alarm tach input.
Grinding the teeth off the flywheel and cracking the starter is not a concern with most modern remote start setups because they will shut the car off for a good period of time in between each start attempt. The multiple firing of the ignition coils is getting very common in recent cars, and many remote start units are now coming programmed so that any signal that oscillates when the engine is running is an acceptable tachometer source.
BK/LG lead is hot in either run or accessory key positions, power windows, radio and wiper motor get power from this circuit. I do not have this circuit live during remote starting. Can burn out wiper motor if the wipers are stuck to windshield with ice and you've left the wiper control switch in the on position last time you were in the car. Reason i'm mentioning this lead is that many car alarm install books list it as a mandatory connection.
W/PK wire is hot whenever the starter is cranking
To access the ignition switch wiring, remove the plastic cover under the 
              steering column, then unbolt the solid metal plate underneath 
  from     the    dash.   Ignition switch wiring will be wrapped in black 
friction     tape,   take   a knife   and carefully cut the friction tape 
to gain access     to the   heavy   guage ignition   switch wires.
                             
                             Crown Vic blower motors draw large amounts of
 current     and   have   been   known   to cause problems with remote start
 units with    onboard   relays.    So   it's probably   a good idea to use
 an external    relay to power  the GY/Y   wire   of the ignition   switch
 harness.
                           
                           
                              
When you attempt to start a PATS equipped vic, the onboard computer sends 
              out a wireless electronic signal that is received by the transponder 
         in   the  key. The transponder then returns a unique electronic signal
      to   the  vics PATS module which in turn tells the PCM its acceptable 
  to   let the  car  run. This all happens in a small fraction of a second 
 and there    are over a quadrillion  possible electronic codes, this security 
   is in addition    to the mechanical  security provided by the cuts on the
   ignition key and   the wafers in the ignition  lock.
                      
Some pictures of PATS keys, note the transponder module embedded in the plastic head of the key.
                             
                              
                               
Some remote starters do not have a dedicated pats bypass module output pin, so you'll need to find an output that is only live when the car has been remote started to attach a pats bypass module. Don't be afraid to open up your remote start unit and probe around the relay bank for a suitable pulsed ground output. The starter kill output pin might seem good at first but remember that many remote start alarms come with an "anti-grind" feature that disables the starter when the car is remote started. Stops operator from toasting the flywheel and starter by accidentally turning the ignition key too far to the start position instead of the on position when initially getting into the car.
Police interceptors do not have SecuriLock, but late model civilian vics/marquis/town cars do.
Various companies sell transponder bypass kits that maintain     the integrity
           of the PATS system when the car is not remote started, but   
when     remote       started provide the proper signal to the PATS computer
which       signals    the   PCM to allow the car to be started. During the
first   couple  years  that  cars   were transponder equipped, there were
only universal    bypass kits avaliable     that consisted of a box to  put
a spare coded  transponder    key in, a system     to selectively engage
the bypass  module,  and an antenna      to place around    the PATS antenna
on the steering column.  But there  are    now ford specific   transponder
bypass units that are considerably    smaller    than the universal   units,
and you do not need a spare key for   them as  they  already have a transponder
  imbedded inside them.
                      
                      The basic procedure for getting the transponder in
the   bypass    module     mated    to your vehicle is to use the securilock
programming     procedure   listed   in  your owners manual to add another
key. But when    it comes time   to program    the new key, instead of inserting
your new   key into the ignition,   press  the  starter button on the remote
control.
                        
                             
                              
                               
If you like living risky and don't care about the factory antitheft system or are temporarily testing, remove the lower plastic shroud of the steering column and tape a securilock coded key onto the column near the ignition switch. If you choose this method, have some generic $1.29 non-pats ignition keys made at the local hardware store first, because having two PATS transponders (one in pats key taped to column, one in ignition key placed into ignition lock) transmit at the same time can cause problems.
Be warned, if your vehicle is ever stolen and later recovered and the insurance
company finds a spare PATS key taped to the underside of the steering column,
they may not pay your theft related claim. The chances of your vehicle getting
stolen in the first place are relatively low. But if the vehicle ever does
get stolen and the insurance company refuses to pay your claim because you
bypassed a factory security device to save a few bucks, it's going to have
a big impact on your personal finances. Bypass modules are cheap (~$30),
new vehicles are not (~$30,000).
                
Year Specific Data:
                
The wiring color code and location information above has been condensed
        into table format and is avaliable here:
         
                Other issues and thoughts:
     
Alarm I purchased had 4 onboard relays, but I still needed 5 external
ones in addition to the onboard ones. Breakdown is 2 for power doorlocks,
1 for starter kill, and 2 for the ticket writing light domelight supervision.
Generic 5 pin 30amp SPDT 12volt coil ones worked well. If you can locate
them, using relay sockets speeds up relay replacement time should a relay
ever fail and makes the install look professional 
                               
                             
                              
                               
                     
After installation, you may be left with some free "channels" on the alarm 
              control module. Some possible uses for the unused buttons and 
  channels         of   the remote include:
                             
Remote start systems:
                
| Part Number | 
                      Description | 
                    
| 1L3Z-19G364-CA | 
                      Gold Remote Start (Keyless Entry & 
  Vehicle           Security) | 
                    
|              1L3Z-19G364-BA | 
                      Silver Remote Start (Keyless Entry) | 
                    
|              1L3Z-19G364-AA | 
                      Bronze Remote Start (Remote Start
Only) | 
                    
| 1L3Z-19G365-AB | 
                      SecuriLock Interface Kit  #1 | 
                    
|             1S4Z-19G365-AB | 
                      SecuriLock Interface Kit #2 | 
                    
|             1L2Z-19G365-AB | 
                      SecuriLock Interface Kit #3 | 
                    
Note: 1998-2002 Civilian Crown Vics require Securilock Kit #1 (1L3Z-19G365-AB). Do not purchase Kit #2 or Kit #3 as they
              are incompatible with the version of the PATS antitheft system
   used     in   98'-02' crown  vics and grand marquises.
                             
Alarm systems:
                
| Part Number | 
                      Description | 
                    
| F7AZ-19A361-AA | 
                      Vehicle Security Systems 1989-2002 
System    6,  Universal,          For Vehicles With Factory Power Door Locks 
(Uses   Siren) | 
                    
|              F5AZ-19A361-A | 
                      Vehicle Security Systems 1995-2002 
System    5,  Universal,        For  Vehicles Without Factory Power Door Locks | 
                    
|              F3AZ-19A361-C | 
                      Vehicle Security Systems 1989-2002 
System    4,  Universal,        For  Vehicles With Factory Keyless Entry (Uses
Siren) | 
                    
|              F3AZ-19A361-D | 
                      Vehicle Security Systems 1989-2002 
System    3,  Universal,        For  Vehicles With Factory Keyless Entry (Uses
Vehicle     Horn) (Does not  include shock sensor) | 
                    
| New PowerCode Part Number | 
                       Most Like | 
                       Description | 
                     
| 2W7Z-19A361-AA | 
                       System 1 | 
                       Keyless Entry | 
                     
| 2W7Z-19A361-BA | 
                       System 3.5 | 
                       Vehicle Security Using Factory Fob
 (Addon    Alarm) | 
                     
| 2W7Z-19A361-CA | 
                       System 5.5 (6) | 
                       Vehicle Security & Keyless Entry
  without     Siren | 
                     
| 2W7Z-19A361-DA | 
                       System 6 (6+) | 
                       Vehicle Security & Keyless Entry
  with   Siren | 
                     
| 2W7Z-19G364-AA | 
                       Gold | 
                       Remote Start with Keyless Entry and 
 Security | 
                     
| 2W7Z-19G364-BA | 
                       Silver  | 
                       Remote Start with Keyless Entry | 
                     
| 2W7Z-19G364-CA | 
                       Bronze | 
                       Remote Start Only | 
                     
| 2W7Z-16A901-AA | 
            Powercode Instruction Manual on CDROM | 
          
Below are a couple wiring diagrams for ford remote starters, the first one is for the discontinued ford remote start gold kit and the second one for the new ford remote start powercode series. Note that there are over 35 wires shown in the diagram, and connecting just one of them to the improper place can cause the remote starter not to function properly or possible damage your vehicle's electrical system. Remote starter kits without keyless entry or alarm functions may have a few less wires, but no matter what kit you choose, you're going to have to splice a couple dozen wires to sucessfully install it. The diagrams below are not meant to intimidate you, but rather warn you ahead of time about the complexity of installing a remote starter into your vehicle.
(click on either diagram below to view a larger version of it)