Alternator warning light wiring

[Pete Whitstone]

I have rewired my gauge cluster, described in another post. However, my new alternator warning light is staying on all the time. I know that I have good charge coming from the alternator, evidenced by both my digital multi-meter, and the actual voltmeter in the car. In the other post, I said how I need to figure out the alternator warning light wiring, as the light was not hooked up yet. So I consult the 1981 EVTM and find this:

So instead of the wire going from a 12v source, through the light and to the alternator like I'm used to, I find basically the same set-up, except it goes from a 12v source, through the light, and to the voltage regulator. The incoming R/LG wire is hot in key-on, goes to the light, then the other side of the light has a LG/R wire going to the voltage regulator. So I cut the LG/R wire close to the voltage regulator, and connected my wire to it. My wire comes from dashboard power, goes through the light, and terminates at the LG/R wire entering the voltage regulator. Should work, right? But no, denied. My light stays on after engine start, even when the dash gauge is showing 14+ volts. So the alternator is clearly charging at that point.

One possible problem is that the alternator warning light is an LED, not an actual light bulb. But I'm pretty sure it is "resistored up" to look like a light bulb as far as load. I'm kind of at a loss to explain why the light is staying on. Anybody have any ideas?

Thanks!

 

[ArdWrknTrk]

Your LED doesn't properly work in that application.

Remember, that a diode will only pass current one direction.

With a filament in this circuit, the bulb goes out because potential on each side is the same.

[Gary Lewis]

Your LED doesn't properly work in that application.

Remember, that a diode will only pass current one direction.

With a filament in this circuit, the bulb goes out because potential on each side is the same.

Another issue with an LED is that it doesn't take much voltage difference to illuminate them. But it takes a lot more voltage differential on an incandescent bulb to get it hot enough to have a visible glow. So put an incandescent in and see what happens.

[ArdWrknTrk]

Another issue with an LED is that it doesn't take much voltage difference to illuminate them. But it takes a lot more voltage differential on an incandescent bulb to get it hot enough to have a visible glow. So put an incandescent in and see what happens.

If it's on all the time, Gary, he is tapped to the excite wire and the other side is grounded.

[Pete Whitstone]

Your LED doesn't properly work in that application.

Remember, that a diode will only pass current one direction.

With a filament in this circuit, the bulb goes out because potential on each side is the same.

Hmmm I was afraid of that. It's hard to find dash indicator lights that are not LED anymore. I'll have to do some searching. Thanks guys!

[Gary Lewis]

If it's on all the time, Gary, he is tapped to the excite wire and the other side is grounded.

Jim - Going back I see Pete said "My wire comes from dashboard power, goes through the light, and terminates at the LG/R wire entering the voltage regulator." So his "light" shouldn't be truly grounded. But perhaps the "dashboard power" isn't on at this point and we are trying to power things in the dash?

Pete - What is your "dashboard power"?

 

[Pete Whitstone]

Pete - What is your "dashboard power"?

It's a key-on 12v power source that supplies power to the gauges and the OP warning light. All new wiring, not factory stuff. The actual path of this circuit is:

Battery + to fuse to relay (controlled by key-on source from factory wiring harness, I think R/LB if I recall correctly) to Alt Warn light (and other gauges/lights, all in parallel) and then back to the voltage regulator LG/R wire.

[Gary Lewis]

Pete - What is your "dashboard power"?

It's a key-on 12v power source that supplies power to the gauges and the OP warning light. All new wiring, not factory stuff. The actual path of this circuit is:

Battery + to fuse to relay (controlled by key-on source from factory wiring harness, I think R/LB if I recall correctly) to Alt Warn light (and other gauges/lights, all in parallel) and then back to the voltage regulator LG/R wire.

I think that approach will work with an incandescent light. But maybe not with an LED. Hopefully you can find a bulb with which to test.

[ArdWrknTrk]

I think that approach will work with an incandescent light. But maybe not with an LED. Hopefully you can find a bulb with which to test.

I be the electron and follow that.

Remember in the stock wiring scheme we run a 512 Ohm resistor in parallel to the bulb so the truck will continue to charge if the bulb burns out.

I would think that's a minimum amount of forward power that an LED would have to pass.

Not sure why or how your led is getting the alternator to charge, Pete, but I'm not too familiar with what the fender regulator is doing V the integral regulator of the 2&3G alternators.

[Pete Whitstone]

Remember in the stock wiring scheme we run a 512 Ohm resistor in parallel to the bulb so the truck will continue to charge if the bulb burns out.

Ah, good catch, I did not even notice that resistor until you pointed it out.

I found some actual incandescent warning lights on ebay, I'll see if they act different when they get here.