Pulsing dash lights

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gtxdude

gtxdude

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Out the other evening for a cruise and turned my lights on and noticed that dash lights were pulsing. I very rarely have car out at night so lights are never on. I shut car off and lights quit pulsing, only when running. Alternator or voltage regulator maybe? doesn't seem to be affecting anything.
 
Voltage regulator. Make certain the regulator has exactly battery voltage. EXACTLY. no less....
 
Have a spare one in the trunk, we'll switch them out and see what happens. thank you
 
gtxdude said:
Out the other evening for a cruise and turned my lights on and noticed that dash lights were pulsing. I very rarely have car out at night so lights are never on. I shut car off and lights quit pulsing, only when running. Alternator or voltage regulator maybe? doesn't seem to be affecting anything.
Click to expand...
What year and model? Points or electronic regulator? Sounds like an old point type.
 
This can be a form of voltage feedback due to poor grounding or harness voltage drop, so main causes are

Indeed, VR especially older mechanical regulator (69/ earlier)

The usual drop in the ignition circuit, bulkhead connector, ignition switch and connector etc

Or poor grounding at the VR to battery

Try making up a good big alligator clip lead with big say, no12 wire. First try clipping from battery POS direct to the junction that feeds the VR and ignition, and if no effect, jumper direct from battery NEG to the VR mount. AKA nearest bolt you can get to, and clean and re-tighten the VR mounting bolts, firewall, and rear of VR
 
Does this only happen at idle or at 2000 rpm as well?

Are your dash lights LED?
 
A bad diode in the alt can do that.

The diodes take the AC the alt makes and turns it to mostly DC.

If a diode or two are bad then more AC to the devices in the car.

Drive it to the local car parts store, they should have a alt tester that they can hook up on the car.

Cheap and easy test
 
Flickering lights are caused a lot of times from the ignition switch contacts being dirty or worn. I had the same problem with my car and I've fixed a few of my friends cars but feeding the wire that typically comes from the ignition switch to the regulator through a relay. I'll look for my schematic and post it here.
 
Dana67Dart said:
A bad diode in the alt can do that.

The diodes take the AC the alt makes and turns it to mostly DC.

If a diode or two are bad then more AC to the devices in the car.

Drive it to the local car parts store, they should have a alt tester that they can hook up on the car.

Cheap and easy test
Click to expand...


I had the same problem.

I changed the alternator and it went away.

It was a bad diode in the alternator.
 
Here's the schematic.

Charging system relay modification (1).jpg
 
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