No voltage on alternator connector pin B (Page 1/1)
Rsvl-Rider MAY 07, 05:32 PM
Battery is not charging on 1986 GT. I'm having problems troubleshooting due to Previous Owner modifications.

The PO replaced the stock gauge pod with aftermarket gauges. In doing so he cut back the wiring harness and spliced in new wires, but the splices are hidden behind the HVAC console and I am trying to avoid disassembling it to gain access.

Since the stock gauges are gone there doesn't seem to be a VOLTS light (which I understand is necessary for the charging circuit to function). He must have compensated for this somehow but I'm not sure how he did it or how to find it to check it's condition. (The new gauge does not have a volts light built in) The car ran and charged with no problems before this non-charging issue so whatever he did was working.

I did some comparison voltage checks next to my 87 GT and I came up with an anomaly. The 87 GT has voltage on pin B of the two connector plug to the alternator when the plug is connected and the engine is running. This would be the black wire (but I think the schematic says brown?) but the 86 has no voltage at that pin. What I don't understand is if the voltage is supposed to be created by the alternator (indicating a bad alternator), or fed to the alternator through the charge indicator lamp (volts light) and generator diode which looks like it is external to the alternator.

Would really appreciate some help with this. Thanks!
theogre MAY 07, 10:13 PM
1. Test the alt by using test light between + battery and alt B.

I think side plug pins can be release w/o cutting.
Release A pin and plug in to alt then use test light for B then start the car.
Note Test Light is On before engine runs.

2. Because some fool did crap wiring you have hard time to find the problem in the car elsewhere....
B pin needs a bulb or 10Ω (1 watt or more) resistor wired to Switch Power.
The reg will not work or fry if B is direct wire to 12v.

Caution: The alt maybe a "1 wire" aftermarket alt so fool didn't bother w/ B wiring. You can't tell by looking unless can find a Name and PN stuck on the alt.
If the alt is dead, can replace w/ SI type you have or CS130 and new side plug either w/ B wired as said.
see https://web.archive.org/web...cast.net/~fierocave/ CS Alternator and Watt story

------------------
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(Jurassic Park)

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zkhennings MAY 10, 01:42 PM
You need a drain on the correct pin on the alt as ogre was saying. The alt pin acts as a ground when the alt is not spinning, and this completes the circuit and the battery light comes on. Then when the alt is spinning that pin goes live and the battery light is no longer grounded and the light turns off. If you don’t have the light, you can wire in a resistor instead, there just needs to be something asking for power on that pin.

On the C500 its pin B3 that goes to the pin on the alt, this wire goes to the battery light on the dash. Check out my thread on C500 and C203 to get a graphical idea of where the wire is and what color it is. It’s nice to have a light light up on the dash if the charging system gets low.

https://www.fiero.nl/forum/Forum2/HTML/146677.html