Below are some notes about installing a 200 amp mitsubishi alternator from a 2009 ford crown victoria police interceptor into a 1998 crownvic that originally came with a 135amp ford 6G alternator.

Here's the alternator we want to upgrade to.

This unit has about 10k miles on it and was in use for about a year before the car was wrecked.

In the northeastern united states, large quantities of chloride road salts are applied to the roads during the winter to melt snow and ice. And this how an alternator looks after just one new england winter.

The pulley on this alternator is clutched due to the high rotating mass of the alternator rotor. The one way clutch locks when rotated clockwise, but freewheels when rotated in the other direction. When car's engine is running, the alternator clutch will be locked most of the time, but it will freewheel during hard acceleration when the transmission shifts cause abrupt changes in the engine crankshaft rotation speed. It will also freewheel when the engine is shut off and the inertia of the heavy rotor keeps the alternator shaft spinning for a bit. Do note that this is just a "one-way" clutch and not an "overrunning alternator decoupler" (OAD) pulley like you'll find in some other vehicles.

There is a little surface rust on the pulley because the alternator sat unused for several months after the car was wrecked. This came right off after the alternator was installed in a car and run for a couple hours with the serpentine belt rubbing against the metal.

Here is the 200 amp tag on the alternator

Now let's take a look at the 135amp sixth generation (6G) ford alternator in the 1998 crownvic that we want to upgrade.

After removing the front engine accessory belt from the alternator

The alternator with the high current charging wire disconnected and the top mounting bracket removed

The alternator top support bracket from the top

The bracket from the bottom. The raised area in the bracket is to protect the fuel rail hose during a very high energy frontal collision.

Here are the 4 mounting bolts for the alternator

After loosening the bottom two mounting bolts, unplugging the regulator connector, and lifting the alternator out

Now that the alternator old alternator is removed, we can try to install the "new" one.

The alternator physically fits on the engine. But, the regulator wiring is too short to reach the regulator in it's new location due to the different location of the regulator connectors on the two different alternators.

Besides the physical length of the regulator wiring, there is also another hidden issue here of this late model alternator regulator being controlled with different electrical signals than this earlier model car generates. But for now, we are concentrating on the physical fitment issues of the alternator rather than the electrical control side.

Here are the two alternators side by side. Note the different location of the regulator connector.

Also, the opening in the ring terminal on the alternator output wire is too small to fit over the alternator output post stud.

The serpentine belt fits over the alternator pulley without any modification.

Also, the alternator top mounting bracket does not fit properly with the new alternator installed. Before the alternator bracket can be slid so that it's bolt holes line up with the alternator and intake manifold bolt holes, bracket hits up against the output charging post. A little work with a 4" angle grinder could likely fix this issue.

Another option is to use the alternator bracket that came with the dorman intake manifold kit. It's got more space open towards the back where the alternator output post is located.

The oem ford 6G alternator bracket next to the aftermarket dorman universal 3G/4G/6G bracket

This is a universal bracket for cars with 3G, 4G and 6G alternators. The 3g tab on the bracket comes a little close to the alternator, cutting this unused tab off would open up some space near the regulator.

Now lets remove the alternator output wire and enlarge the ring terminal with a 5/16" drill bit so that it will fit over the new alternator output stud. The old alternator uses a M6x1.0 stud on the output post, the "new" alternator uses a M8x1.25 stud instead.

Before modification

After modification

Now that the charging wire hole has been opened up, we can connect the alternator output wire and begin tinkering with the control aspects of the new alternator regulator.

This alternator will self excite without any regulator wires connected at all, but charging voltage will only be 13.6 volts under minimal load which is too low for good battery recharge characteristics. So we need to find some way to raise the voltage output of the alternator. My first idea was to use the alternators no-pcm-communication failsafe voltage setpoint and insert a diode or two inline with the voltage sense terminal to make the alternator think that the battery voltage was lower than it actually was.

In introductory electrical theory textbooks, you'll read that a diode always drops 0.7 volts across it. But in the real world, the voltage drop across a diode varies as a function of current and various other parameters. This causes the alternator output voltage to float around some as the car runs and things heat up. At first, i was only getting around a 0.4V drop across each diode, but later this started to ramp up close to 0.7V across each.

Maybe some high current diodes like those in a marine battery isolator could have solved the voltage float problem mentioned above or maybe a voltage divider consisting of a couple resistors could have been installed instead. But a cleaner solution is to send the alternator fake voltage setpoint data on the gencom line. This way, the alternator will think that it's installed in an actual car recieving voltage setpoint requests from the powertrain control module (PCM).

The 2003 and later crownvic alternators have a PCM controlled alternator regulator. There are two unidirectional control lines going to the regulator. The gencom line has information on it about what voltage the alternator should output. And the genmon line has information about what load the alternator is under, any problems the alternator may have, and various other operational data.

Unfortunetly, the 2002 and earlier crownvics control their alternators differently. The voltage setpoint inside the regulator is fixed and non-adjustable. And rotor field coil excitation voltage is obtained through the instrument cluster i-line to tell the alternator when to turn on/off the rotor magnetic field.

But if we place a 125Hz pulse width modulated (PWM) square-wave signal on the alternator gencom line of our "new" alternator, we can vary the alternator voltage setpoint by changing the duty cycle of the waveform.

A search for pwm circuit ideas revealed that there are a number of premade pwm circuits on the market catering to the HHO hydrogen generation crowd. The idea is that you can extract hydrogen from water which can then be fed through an automobile's engine air intake system to increase fuel economy. Many of these circuits were originally intended to control the speed of electric motors, but we can retask them for our alternator control project if they have an output frequency close to 125 Hertz and they are designed to control motor speed through the ground side of the circuit.

After looking at a few different circuits, i settled on the MX066 from bakatronics.

This circuit is based on the LM324 operational amplifier (opamp) and is designed to handle up to 30amps which is more than adequate for our alternator voltage regulator control application. The 100Hz frequency of this unit is somewhat close to 125Hz that ford generates inside the pcm to control the alternator. But if we want to raise the frequency of the pwm to 125Hz, we will need to lower the resistance of R4 in the circuit.

This circuit turned out to work very nicely to control the alternator even though the frequency of the pwm waveform is 25 Hertz slower then the ford gencom specifications in it's unmodified form.

For our project, we want to crimp three 1/4" spade terminals onto 3 peices of wire and insert them onto these tabs. We will be using the G, -M, and +12V terminals. The +M terminal will be unused since it jumps directly to the +12V feed and our alternator already has an internal source for +12V.

After crimping the wires and sliding them onto the circuit board

After inserting the circuit board into a case so that the traces don't accidentally short out against metal objects

The red wire is +12V, the grey wire is ground, and the white wire is the pwm output to feed the alternator gencom line.

Here's our testbed vehicle with the 2009 alternator installed. A new voltage regulator wiring pigtail was purchased, and one wire of the new pigtail inserted into the appropriate pin of the old regulator connector to read battery voltage. The middle gencom wire is connected to the output of the pwm device. Turn the pwm control knob counter-clockwise and we can raise the voltage setpoint of the alternator regulator close to 15Volts. Spin it clockwise and the setpoint will dip down below 12Volts at the other end of it's travel limit. The alternator voltage setpoint is very stable with batery voltage only varying +/- 0.01 Volts given a constant load on the car's electrical system.

Good battery recharge characteristics are obtained somewhere between 14.0 Volts and 14.5 Volts at a reasonable ambient temperature. The regulator in the factory installed 1998 crownvic alternator had a fixed setpoint of 14.4 volts according to transpo, but battery voltage was actually 14.1Volts at idle with the engine running and all accessories turned off according to my voltmeter.

This is a really powerful alternator that ford under-rates. If you spin the alternator really fast and the ambient temperature is low, you can get well over 200 amps out of this unit.

Here is a reference picture of a wrecked 2005 crown victoria engine with the alternator and it's wiring attached

(picture courtesy of Steve83 on

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