1985 P'up. Battery light stays on when truck is off.

[Big-E-85-pup]

I have put in a new voltage regulator when I got the truck because it was not charging. Just presently the voltage light came on when the truck is off and the key is out. The light would go out when the truck is running and it does charge. I have put a new one in but that did not fix it. I tested all the relays I could find under the hood with a multi-meter and all had where good.

[isuzu Specialities]

The power to the alt warning light is always live. The N terminal on a external regulator or the L terminal on the alternator with internal voltage regulator will always be shorted to negative when the key is on and engine is off. When the alternator begins to produce current the N or L terminal will switch polarity from negative to positive. The alt warning light cannot turn on with positive voltage on both connections. This what turns off the alt warning light on the dash.

So you have a few possible reasons for the light never turning off.
the first is the voltage regulator is not switching polarity as it should. Being that this circuit is isolated form the circuit that supplies charge current to the battery your alternator will still have 14V output.

The seconded thing is the wiring between the light and the voltage regulator is shorted to ground & keeping the light on regardless of what polarity the regulator L or N terminal is.

[Red Truck]

Plz let us know what it eventually takes to correct this, as I don't think I've ever heard of it before. However, after reading a little about it, it doesn't sound too uncommon. Some fix actions I've read ranged from the instrument cluster (that's kinda vague) to the ignition switch. It's just weird. /R

[Big-E-85-pup]

I have another voltage regulator on the way. The brand new one broke (what a surprise parts from china are worthless). I will look into the ignition switch. I really hope its not the whole cluster.

[Big-E-85-pup]

Hey, sorry it been so long. Had training for work most nights, and not been able to really get out to test things. This past weekend I got a wiring diagram and I am kind of lost. The ignition switch is good for all other things. It seems like the ignition switch will turn off the light when it is rolled forward. In my inexperienced thinking the switch is completing and breaking grounds to make the lights work. So maybe the ignition switch? These past couple nights I have been driving in the dark and have noticed that almost none of the lights work for my cluster. The only ones working are my high beam indicator and the blinker. So is the cluster bad? How do I test that?

[JoeIsuzu]

Hey, sorry it been so long. Had training for work most nights, and not been able to really get out to test things. This past weekend I got a wiring diagram and I am kind of lost. The ignition switch is good for all other things. It seems like the ignition switch will turn off the light when it is rolled forward. In my inexperienced thinking the switch is completing and breaking grounds to make the lights work. So maybe the ignition switch? These past couple nights I have been driving in the dark and have noticed that almost none of the lights work for my cluster. The only ones working are my high beam indicator and the blinker. So is the cluster bad? How do I test that?

You said earlier that you were replacing the voltage regulator, right? Did you replace the one in the alternator, or did you add an external one? Once you tinker and make it non-standard, none of the expected "rules" apply anymore, and it's hard to help.

But the actual way to "test" the lights in your cluster is to turn the ignition ON without starting the truck. All lights should come on then, if I'm not mistaken.

Jack

[Big-E-85-pup]

I replaced an external one. The oil, voltage, seat belt, and brake lights work. I am talking about the ones for the speedometer, fuel, and temp that are not working.

[gruff54]

You mean the instrument panel backlights? The lights that allow you to see the gauges at night?

Mike

[isuzu Specialities]

Hey, sorry it been so long. Had training for work most nights, and not been able to really get out to test things. This past weekend I got a wiring diagram and I am kind of lost. The ignition switch is good for all other things. It seems like the ignition switch will turn off the light when it is rolled forward. In my inexperienced thinking the switch is completing and breaking grounds to make the lights work. So maybe the ignition switch? These past couple nights I have been driving in the dark and have noticed that almost none of the lights work for my cluster. The only ones working are my high beam indicator and the blinker. So is the cluster bad? How do I test that?

The ignition switch functions by supplying positive voltage to the devices that are connected to it. If the battery light turns OFF when the ignition switch is turn ON. This means the ignition switch is supplying + voltage to one side of the light bulb as it is supposed to. The issue must be with the other 1/2 of the circuit which is the controlling side. The voltage regulator is what controls the voltage to the other side of the light bulb. When the alternator is NOT producing power the wire to the light bulb is negative. When the alternator is producing power the wire to the bulb is positive. Perhaps your voltage regulator is simply wire incorrectly?

Your dash light are a separate issue. Your high beam indicator light in the cluster works because it is part of the headlight/high beam circuit. Your turn signal indicators in your instrument cluster work because they too are a part of the turn signal circuit. Even though these indicators are located within the instrument cluster assembly they are both isolated circuits. They are 100% independent of all other devices within the cluster.

The Cluster illumination circuit is controlled by your headlight switch and is connected to the marker light circuit.
To pinpoint the fault knowing if the other circuits work normally will point you in the proper direction to begin troubleshooting.

Does your taillights and marker lights work?
If your tails and marker lights work, that tells you the fuse and the on/off switch for your dash works as it should. Meaning that your problem is somewhere "up river" form the switch.

Does your vehicle have a dimmer switch for the dash lights?
At this point verifying the dash lights are getting power from the switch (&/or dimmer switch) and a ground connection to the chassis by using your test light is the next step.