Alternator Lite 1986 Grand Marquis

I replaced the Battery because of a dead cell. Replaced Alternator because dead cell killed it. Replaced alternator again cause I got a bad one at Pep-Boys. Get intermittant ALT lite. Previous experience indicates bad voltage regulator… Is there anything else I need to look for before I replace alternator/V.R. again???

Ensure wiring/connections and grounds are clean and wrench tight.

Have a load test done on the charging system (in vehicle).

Did that… The new alternator passed the load test. All wires have been verified, and cleaned when necessary. Only thing not working now is Radio, but I think I didn’t put in the fuse correctly… I’ll have to check that. Nothing happened today, but last nite I had a lite most of the way home, and then all of a sudden it went off, and the lights brightened up and the car took off down the highway… Thank you for responding. :slight_smile:

I think on that year the PCM (didn’t they call it ECC then?) has control of the alternator. You may have a problem with it, or the connections to it.

I had a Windstar do this. Look for a fuse that says something like “fan relay to PCM”. What was happening with my van was that the PCM was supposed to increase the output from the altenator when the fans kicked on but the fuse was blown so it didn’t know when the fan was on. The increased amps from the fans (60 watts) was enough to kick on the battery lite.

The PCM does not control the alternator, it has a internal regulator. This is the description of how it operates from ALLDATA. If the light is staying on there could be a problem with alternator voltage from the I terminal or a short in the indicator light circuit.

A charge indicator lamp or ammeter can be used in charging system.If a charge indicator lamp is used in the charging system, Figs. 1 and 2, the system operation is as follows: when the ignition switch is turned ON, a small electrical current flows through the lamp filament (turning the lamp on) and through the alternator regulator to the alternator field. When the engine is started, the alternator field rotates and produces a voltage in the stator winding. When the voltage at the alternator stator terminal reaches about 3 volts, the regulator field relay closes. This puts the same voltage potential on both sides of the charge indicator lamp causing it to go out. When the field relay has closed, current passes through the regulator A terminal and is metered to the alternator field.If an ammeter is used in the charging system, Figs. 2 and 3, the regulator 1 terminal and the alternator stator terminal are not used. When the ignition switch is turned ON, the field relay closes and electrical current passes through the regulator A terminal and is metered to the alternator field. When the engine is started, the alternator field rotates causing the alternator to operate.Some vehicles are equipped with electronic voltage regulators. These solid state regulators are used in conjunction with other components in the charging system such as an alternator with a high field current requirement, a warning indicator lamp shunt resistor (500 ohms) and a wiring harness with a regulator connector. Some 1985—87 vehicles are equipped with Integral Alternator/Regulator (IAR) charging system. This system has a solid state voltage regulator located in the rear of the alternator. When replacing system components, note the following precautions:

That’s odd. I’ll take your word for it. The PCM did control the alternator in the 85 crown vic that I had.

This car doesn’t have an electric fan, but I could have sworn that the PCM did control the alternator. Willey says no.