'85 SA/2: Radio voltage at 2.5 Volts when lights on
 

Hi,
everytime I switch on the headlights, the voltage of the Radio drops down to 2.5 V and the radio turns of. Where is the error, what can I do?
Thank you.

Is this when its running? Need some more context.

Yes, the motor was running.
I can give you every detail you have to know, but I don't know what is needed.

So you either have a bad battery, a bad alternator or a short when the lights are lit.

1. Have battery tested to see that its good. Usually if it holds 13+volt charge its good. Here we have autoparts places that test batteries for free.
2. Your alternator is not charging the battery sufficiently. When running, the voltage at the
positive terminal should be 13-15 volts normally, less means the alternator is weak. Again we
can go to an autoparts store and have it tested to make sure.
3. You have a short when the lights are lit. Use a DVM to check your voltages at various points
in the harness to see where a big voltage drop happens. Usually hard to find. Look for
physical issues in the harness like scrapped or exposed wires.
4. Could be a bad ground as well.

1. The battery is very good.
2. The alternator is good too.
3. Can you give a hint where those points could be?
4. How can I be sure to have a good ground?

So maybe you have a short happening when the lights are on. You could try unplugging the
lights at the bulbs and see if it still happens. If it does then you have narrowed it down to
the wires that control the light movement. If it doesn't then its in one of the light circuits.

Another thing to try thats even easier is to turn on the lights but then lower the buckets with
the switch on the console. Again that would help you eliminate which circuit is at fault.

It could just be something is grounding out or pinching when the buckets move.

The ground points are at 4 places I can think of:

1. Is on the left hand shock tower about /12 down, the negative cable from the battery goes
there and then on to the starter (front chassis ground)
2. The negative cable then attaches to the bolt on the starter (engine ground)
3. Up under the dash is a ground wire for the cluster. Its just above the steering column and you
can only see it by being down by the brake pedal and looking straight up (interior chassis ground)
4. The exhaust has a braided pigtail that attaches to the exhaust hanger mounting bolts on
the chassis and then to the muffler at the hanger connection (rear chassis ground)