914 G light Out Options

[frankc]

Good Afternoon,

I have searched and read on this site and PP on alternator/charging issues. I followed the guidelines on PP when the light is out and now feel the issue is pointing to the alternator.

Background:

This 74 2.0 has sat for 14 years (ran when parked) and I towed it home a few weeks ago. Following guidelines here and PP, I was able to revive the engine on Sunday.

I have a number of issues from just sitting and I am knocking them out one by one.

Problem: G light is not lit when I turn the ignition key.

Checked the following :

1. Bulb tested good out of socket.
2. 0V at the blue wire on the instrument end.
3. Continuity to the harness at the relay board is good.
4. 0 volts at PIN 2 of the big connector (D+)
5. Relay board traces between alt harness pins and VR check out fine.
6. Cleaned tranny ground strap.
7. 12.1v at the battery while running.
8. Swapped out VR from my 1.8L - no change.

Have not checked the belt (it may be missing- seriously) tension yet.
Have not peeled back the tin to check the alt harness wiring (DF connection).

Have I missed anything?

Electrically, the car is coming around - most everything works except the headlamp doors do not pop up and the fog lights do not work. Perhaps the contacts or the light switch.

Thanks!

Frank

[lapuwali]

+12 should be on both sides of the bulb with the key on. If you have 0V on the blue wire with the bulb in place and the bulb is OK, then check to make sure you have 12V on the other side of the bulb. If you do, then the bulb socket is flakey. If you don't have 12V to the socket, then check the fuse (can't remember which one, 8 or 9, I think), and go backwards from there. +12 has to be SUPPLIED to the alternator to charge the electromagnetic coils, and this comes from the battery through the ignition switch and that bulb.

When you first turn on the key, the battery supplies +12, and it flows through the bulb to the alternator, through the coils, and thence to ground, so the bulb glows. Once the alternator starts to charge, a voltage is generated on the D+ wire, so the voltage difference across the terminals of the bulb drops to 0, so no current flows through the bulb, which goes out.

[frankc]

I took the gauge back out, cleaned the terminals to the socket and measured the voltage at the blue wire - 0v withthe key on.

Checked continuity again between the harness - that checked.

Took out the VR cleaned the socket that it plugged into. I noticed when I tried to re-insert the VR that it did not appear to be in the socket correctly. So I opulled the board and did it outside the car to ensure it was correct and fully seated.

Connected everything together - now the Generator light is on. I think it was the VR socket needing cleaning or the VR not being correctly or fully seated.

Have not cranked it yet to see if it will go out above 2k.

Thanks for the tip!
Frank

+12 should be on both sides of the bulb with the key on. If you have 0V on the blue wire with the bulb in place and the bulb is OK, then check to make sure you have 12V on the other side of the bulb. If you do, then the bulb socket is flakey. If you don't have 12V to the socket, then check the fuse (can't remember which one, 8 or 9, I think), and go backwards from there. +12 has to be SUPPLIED to the alternator to charge the electromagnetic coils, and this comes from the battery through the ignition switch and that bulb.

When you first turn on the key, the battery supplies +12, and it flows through the bulb to the alternator, through the coils, and thence to ground, so the bulb glows. Once the alternator starts to charge, a voltage is generated on the D+ wire, so the voltage difference across the terminals of the bulb drops to 0, so no current flows through the bulb, which goes out.