Hey all here lately I have had some issues with my charging system. When it's running with no loads I get right arround 13.3- 13.4 v but when I put a load on the system( headlights, fan, Blower motor, ect) the voltage will drop and not raise back up. As low as to where it's not charging at all11.4v is the lowest. All this started when I has a FD alt on the car so I downgraded to a stock s4 alt and after several replacements from autozone still no luck.
The car is a 87 N/a with as4 turbo engine and harness. My 2 wires for the alt plug have b+ voltage running and key on only the top terminal has b+ and nothing on the bottom.
I have good connections at the alt. Battery, and starter. As well as the batt- block ground and a extra from batt-strut tower.
Any help or tips or anything?? Do I possably have the alt wired wrong??

 

It's possible that the problem is the weak amperage created by the S4 alternator. In reviewing your post the W/B wire when connected to the alternator and key to on but engine off should read 1 to 3 volts. When it does the center dash warning lights come on but then go off when the car is started. If you have problems backprobing the W/B wire you could stick it with a pin and take the reading from the pin. Also, you could take the reading from the W/B wire at the CPU. This wire can be found at the bottom of the CPU in the 4 wire plug. If the quarters are tight you could stick a wire into the back of the W/B wire and take the voltage reading from that.

In addition you could take a meter lead to the B+ terminal (Black cable) and the other meter lead to the positive battery post (not clamp) and the reading with the engine running should be less than 20 millivolts and this measures the positive side to the charging system such as the wires connections. Also, placing one meter lead on the alternator casing and the other lead to the negative battery post (not clamp) and the reading also should be less than 20 millivolts with engine running. This measures the grounds related to the charging system.

 

well i have good power and ground but i lack the 1-3v on that circut. like i said the other wire has 12v with key on and when running it has charging voltage but the other circut has nothing unles its running and when its runnign it has charging voltage. where does this refrance voltage come from? is it internal to the pcm? and if so is there a way i can bypass it or use another voltage sorce to trick the alt into working so to say?
my charging light on the dash has NEVER worked fom the time i got the car 5 years ago and up untill now i havent had any issues.

 

All the warning lights in the dash should come on w/key to on, engine off, except the brake light unless it is engaged. Then they, the lights, turn off when the car is started. I believe the W/B wire is an output wire and if so then the problem or lack of voltage on the W/B wire would be an internal one.

 

The s4 alt is wired differently from the s5 alt and FD alt. Did you flip the proper two wires when you did the swap? If not then search the forums for FD alternator upgrade to see what I mean. Or get an s5 (1989-1991) alt if it fits. Just make sure the shape and so on are the same, I dunno if it is.

Otherwise the charging system is basically alternator + battery + wires (including grounds, battery terminals and other connections). The voltage regulator is inside the alternator so it gets replaced with the alt and usually makes the voltage too high when it fails or the plug in back gets disconnected. Not too low. So if it's not from two wires being switches then alternator, battery or wires are bad. Autozone will test the alternator and battery for free.