thebornotaku
( ͡° ͜ʖ ͡°)
- Joined
- Nov 21, 2008
- Location
- Rohnert Park, CA
AFAIK the battery light is in-line with the exciter circuit. Turn the key to the run position but don't start the car. If you get no battery light, there's a fault in the exciter circuit.
Luckily all the connections on that circuit are relatively easy to get to.
Firstly, check all your fuses. This should be a no-brainer. Replace the dead ones. IF there are no dead ones, or this doesn't help, keep going...
Pop your hood and check the little female spade connector that hooks up to your alternator. Clean off any corrosion if there is any, and ensure that it's connected properly. Check for batt light. No light? Keep going...
Here's where it'll get a little harder but still not too difficult. Pull the cluster. You do this by removing the trims (or gauge bezels) to the right, pull the headlight and dimmer knobs off, pull that trim out, disconnect the rear fog switch, then unscrew the four screws holding the cluster in. With the wheel at 12 o'clock, slide the cluster towards you. Disconnect the wires and remember where they go (there should be the red/white tach wire, the full-circle connector, the half-circle connector and maybe a speedo wire? I have a cable speedo on my '85 so I'm not sure how the elec ones work...). Slide the cluster to the right and once you have it free, inspect the pins for any corrosion or damage. Then find which one is your battery light and pull it out. Is the light blown? If so, replace. Re-install your cluster, but do it loosely. don't screw it back in or anything, but make sure to reconnect everything. check for battery light. No light? keep going...
aaand here's probably the hardest part: If you've reached this point then likely it's not a connection and instead it's a wire issue.
EITHER...
1. Grab your multi-meter and start doing continuity tests. You'll probably need some jumper wires. Figure out which pin for the cluster sends the 12V exciter signal to the alternator and probe that pin. Put the other lead on the exciter wire at the alt. There should be no resistance. Likewise, do that again for the other legs of the circuit.
OR...
2. Grab your test light and go probing around. Hook it up to 12V power and probe the pin that sends the signal to the alt to check for ground (just another way of doing the continuity test). It should light up with the car off. If it doesn't, there's a break in the wire somewhere. Start the car. The light should go out. With this test you're essentially replacing the normal battery light & circuit with your own 12V exciter voltage. If the light goes out, then there's an issue with power getting to the battery light. IF the test light stays on, then there's a short to ground somewhere.
Basically your alternator can't produce amperage without a little shove as it were -- and the circuit that kind of kicks the alternator on goes through the battery light. IT feeds it 12V to excite the magnetic field and begin it producing voltage. That's why when the car is off but the key is on, the battery light is on. Once you start the car however, the alternator takes that magnetic field and energizes, and starts producing 12V (or 13.8 or whatever). IT backfeeds that 12V up the exciter wire and since there's no voltage differential between the feed to the light (12V constant) and the feed from the light to the alternator (which varies between a ground and a 12V feed).
edit\\
I'll disagree with belt tension (because I reckon that would make a hellacious skreech if it were loose, and overheating if it were missing), but everything else here is good, and even a few points I forgot about. Check your grounds. I think the alt grounds to the engine block, then the engine has a ground cable on the intake side near the distributor that goes to the battery. Cleaning your battery posts and terminals is also one of the first things I suggest people do whenever they have any electrical issues. It's the easiest to get to and one of the most important connections in the car, why not take 2 minutes to scrub the mating surfaces clean and rule it out?
Luckily all the connections on that circuit are relatively easy to get to.
Firstly, check all your fuses. This should be a no-brainer. Replace the dead ones. IF there are no dead ones, or this doesn't help, keep going...
Pop your hood and check the little female spade connector that hooks up to your alternator. Clean off any corrosion if there is any, and ensure that it's connected properly. Check for batt light. No light? Keep going...
Here's where it'll get a little harder but still not too difficult. Pull the cluster. You do this by removing the trims (or gauge bezels) to the right, pull the headlight and dimmer knobs off, pull that trim out, disconnect the rear fog switch, then unscrew the four screws holding the cluster in. With the wheel at 12 o'clock, slide the cluster towards you. Disconnect the wires and remember where they go (there should be the red/white tach wire, the full-circle connector, the half-circle connector and maybe a speedo wire? I have a cable speedo on my '85 so I'm not sure how the elec ones work...). Slide the cluster to the right and once you have it free, inspect the pins for any corrosion or damage. Then find which one is your battery light and pull it out. Is the light blown? If so, replace. Re-install your cluster, but do it loosely. don't screw it back in or anything, but make sure to reconnect everything. check for battery light. No light? keep going...
aaand here's probably the hardest part: If you've reached this point then likely it's not a connection and instead it's a wire issue.
EITHER...
1. Grab your multi-meter and start doing continuity tests. You'll probably need some jumper wires. Figure out which pin for the cluster sends the 12V exciter signal to the alternator and probe that pin. Put the other lead on the exciter wire at the alt. There should be no resistance. Likewise, do that again for the other legs of the circuit.
OR...
2. Grab your test light and go probing around. Hook it up to 12V power and probe the pin that sends the signal to the alt to check for ground (just another way of doing the continuity test). It should light up with the car off. If it doesn't, there's a break in the wire somewhere. Start the car. The light should go out. With this test you're essentially replacing the normal battery light & circuit with your own 12V exciter voltage. If the light goes out, then there's an issue with power getting to the battery light. IF the test light stays on, then there's a short to ground somewhere.
Basically your alternator can't produce amperage without a little shove as it were -- and the circuit that kind of kicks the alternator on goes through the battery light. IT feeds it 12V to excite the magnetic field and begin it producing voltage. That's why when the car is off but the key is on, the battery light is on. Once you start the car however, the alternator takes that magnetic field and energizes, and starts producing 12V (or 13.8 or whatever). IT backfeeds that 12V up the exciter wire and since there's no voltage differential between the feed to the light (12V constant) and the feed from the light to the alternator (which varies between a ground and a 12V feed).
edit\\
I'll disagree with belt tension (because I reckon that would make a hellacious skreech if it were loose, and overheating if it were missing), but everything else here is good, and even a few points I forgot about. Check your grounds. I think the alt grounds to the engine block, then the engine has a ground cable on the intake side near the distributor that goes to the battery. Cleaning your battery posts and terminals is also one of the first things I suggest people do whenever they have any electrical issues. It's the easiest to get to and one of the most important connections in the car, why not take 2 minutes to scrub the mating surfaces clean and rule it out?
