As soon as I replace the 20A fuse in my 1982 it blows immediately and you can see tiny blue flashes in the fuse holder.

Started looking for a ground short but no luck so far.

I checked all bulbs (LH and RH courtesy, dome, glove box) - there weren´t any! Checked and took out dome light switches near the hinges - looked good. Checked and unplugged cigar lighter - no signs of grounding whatsoever. Took out orange timer box behind the glove box compartment - looked good, but anyways. Unscrewed and lifted the shifter plate - found the A/C connector unplugged and plugged it in, all other connectors and switches etc. looked ok.

Hooked up a test lead with a light to the cold side of the fuse and measured resistance to ground - near zero. Ran the test light to 12V from battery - light on. Unplugged both antenna relais - light on. Unplugged seat belt switch - light on (not sure if it´s on the same fuse).

What else can I check and how can I narrow down the area that probably has the short to ground?

 

Does the 82 have a light in the rear compartment when the door or back is opened?

 

Did you maybe installed something new that caused a wire to brake or something?

 

Power door locks are on that circuit. This source says that the A/C compressor is on the circuit as well.

 

No light in rear, no hatch. Unhooked a/c as well - no change. Also checked spare tire light - looks ok. Is there a light in the engine compartment somewhere?

No new installs from my side but only got car recently. There is or rather was a stereo install but radio has been taken out by previous owner. The connectors look pretty ok, though.

I was hoping not to have to take the door panels off to check. Can I somehow measure if the short is in the doors?

 

Look just above the hood support.

 

Did you check the power door locks? The switch connectors are known for breaking.

The underhood light is on another circuit--actually unfused--but it has an integral fusible link.

In general, anything that has power with the ignition switch in the "off" position is powered by that circuit. Don't you have an oil temperature gauge in the gauge pack? If so, power from the ACC circuit is available at the radio as the factory versions had a digital clock; if not ACC circuit power goes to the gauge pack. In earlier C3s the ACC circuit also powered the alarm system but it should be a separate circuit in yours.

Do you have a light in the passenger side vanity mirror? If so, the two-conductor connector is very close to the courtesy light delay timer. It should have one orange and one black wire.

The courtesy lights have constant +12V electrical supply and the various switches that operate them work by providing ground to the circuit. If I had to guess at a likely place for a short to ground, it would be in the wiring to the light in the "T" top bar--particularly where the wiring enters the "T" at the rear.

For the very reason that it has constant power, the ACC circuit is very frequently tapped for aftermarket accessories.

 

I'm not sure if it's the same on an '82, but I dropped a washer in the lighter socket once and had the same problem you're experiencing.

 

Should be there, but isn't. But I guess this is the connector, right there in the LH inner fender.

 

Not yet. You are refering to the pigtails at the back of the switch in the door panels, rights?

No light in the visor, but the connector is there.

 

Is it likely to have a short in the headlight switch?

 

No, because the headlight switch only provides a ground path to the courtesy light circuit. There is no +12V from the ACC circuit in the headlight switch. If there were a short to ground in the switch it would be taking out a different circuit.

 

Yes, I'm referring to the connectors to the door lock switches behind the door panels. If you find actual pigtails spliced in then they're already been replaced. From the factory the wiring is continuous. Of course merely replacing the connectors doesn't mean properly replacing them

 

Is there any chance you could borrow a Power Probe from anyone? Please don't buy one, they're not cheap. You will find the short, it will just take a little longer.

 

Will check.

With other cars I found the wires in the grommet from door to body damaged from opening and closing the door.

 

Don't think so. Basically, is there any difference to a lead with a test light from the battery?

 

I'm looking at a '79 schematic so wiring might have changed even if I very much doubt so with the power lock circuit.

Both of the lock switches get constant power from the CTSY (ACC) circuit. Near where the grommets go into the door you should find two-wire connectors containing an orange and grey wire. Disconnect them at both sides and it will eliminate the possibility of a short going into or inside of the doors.

 

The power probe is pretty cool, with the fuse out of the circuit,you can energize individual wires with battery voltage to check for shorts. The probe is protected with a internal circuit breaker for when you find a short to ground. It doesn't matter, with some patience you will find the short because it's not an intermittent condition.

 

Go back to the orange timer box, remove it and connect the two white wires and then try a new fuse and see if that box is the problem.

 

The box has been removed. I didn't connect those wires, though.