Question1987 Mustang Coupe v8
My recently purchased car has a new battery and alternator both of which have been tested and I am still only showing 11.9v at the battery when the car is running...........
-New alternator thats already been checked (internal VR)
-87 coupe former 4cyl car
-Car was sitting for a month and when I went to test it the owner charged the battery and installed the battery leads backwards resulting in the smoking of the starter solenoid and a fusible link to the ignition. (Has been repaired)
My problem is my alternator is not putting out anything. I'm getting 12.2v with the car off and 11.9 or so with the car running and the indicator light in the dash is on. I've checked the wires too and from the alternator and they all have continuity. My problem with using a wiring diagram is that I don't know if there is any difference between a 4 cyl alternator harness and a 8cyl alt. harness.
All together there are 6 wires at the alternator. 3 in each plug. Both thick black wires have ~12v with the car running while the creamy white wire that runs to the other alternator plug only has .1v. It seems that it's a signal wire possibly from the voltage regulator to the other harness. Is that the case and if so is that too low of an output???
The other harness has a yellow wire (also with 12v running) a green wire with 5v and the same creamy white wire that jumps from the other alternator harness.
The negative battery terminal was extremely corroded and was replaced. The 2 thick black wires from the alternator harness splice into 1 six inches from the alternator plug and are also very corroded. Is that a factory splice or was it rigged that way?? I plan on replacing the two black wireswith a completely new wire tomorrow from the alternator to the solenoid.
Any ideas on whats going on? The wiring other than the corroded thick wires from the alternator seem fine and have continuity which would make me think its the alternator but it checked out fine. Help
AnswerJacob, if I understand you correctly, the V8 Mustang used to be a 4cyl? That sounds like my son's Ranger that I put a 302 in a year ago! And the modifications are not fun.
The alternator circuit is fairly simple, but I don't know how the conversion was made... you'll have to check each wire to see if they run where they should, and colors may not be the same all the way to the point of origin.
C153 on the alternator has 3 wires - two of them are the same thing, Black with an orange stripe, go to a fusible link that goes to another fusible link at the starter relay on the fender. Make sure they have power at all times.
C154 has a Yellow/white wire that is basically the same source of power, and also connects at the starter relay.
C154 has a light green/red stripe wire that goes to the warning light - it supplies the voltage to energize the alternator field current when the key is on... if it is only .1v, you probably have a blown fuse in the dash fuse panel. Without this voltage, the alternator will not charge.
C154 and C153 have a white/black stripe wire that connects the sense voltage of the regulator to the alternator windings.... it will rise once the alternator is charging again.
Sound to me like you have already found the problem - a loss of the field exite voltage - and the cause is either a blown fuse or blown indicator bulb or broken wire from the fuse panel to the alternator. You could test this by applying 12v to that wire with then engine running, and the alternator should start charging. This voltage is supplied only with the key on, to prevent battery discharge when not running.
Hope this helps,
Clay
