Electrical Short in 1983 Cabriolet

[1983Cabrio]

My '83 cabriolet had a weird thing happen. The Tach started going haywire, jumping up and down. Then, all of the lights went dim, the radio went out when I stepped on the brakes, then the high beams stopped working. Yes, the battery was dead.

Now, my car's battery has been dying after 3 days of non use, so I figure it's a short.

Question - When I test the Fuse bar (with the battery removed) there is NO WAY it should have continuity with the ground for any reason, right? Except a short somewhere? No reason there would be ground continuity with the starter, or alternator? - I removed the fuse box from the body (in chance of a mounting bolt shorting it out) and it still beeps with ground...

How should I start finding the short? I'm sure it burned out the voltage regulator.

Thanks for your help, sorry for the long message.

[porwolf]

If you suspect a short somewhere in your system I would take all fuses out. On all the fuse outputs, the side that goes to the various car components I would check for shorts with a Volt/Amps/Ohm meter. Then I would put the fuses back one by one and see whether that part of the circuitry works. Maybe you get lucky this way and seriously narrow down the problem area.

[DBDP]

I would start by testing for a draw.

Remove the neg terminal from the battery and place a test light between the neg post and the neg battery harness. Make sure you have nothing on, including accessory lights, like door open...

If the test light is lit you have a draw. Start disconnecting harnesses when the light goes out you know your draw or short is in that harness. Slowly work your way down the harnesses until you pinpoint the location then dive into the electrical components.

I have used this method many times and have founds some silly stuff, like a seat cover that was pulling the power seat button up. The driver didn't notice because he rode with the seat in the highest location normally.

Hope this helps

[timmy2]

There will be some continuity to ground on some circuits through the devices in the multiple circuits. The meter applies a small voltage to measure the resistance and it will go through things like lamps, coils etc.
You are better off to put an ammeter in line with the battery negative and measure the draw in normal configuration and then isolate each circuit by removing fuses to narrow it down.
The trunk lamp is one of the usual suspects!

[Cooper911SC]

The description you give is a classic sign of problems with a stuck voltage regulator overcharging your system.

Did you happen to notice a sulfur gas smell at the front of the car? Or inside the trunk?

The battery will die due to over charging, as all of the water gets boiled off.

I would replace the (now dead) battery with a new one, check the voltage at rest, should be about 13.2 volts fully charged new battery, start the car and check the voltage at idle and 2k rpm.

The regulator should limit the charge voltage to about 13.8 to 14.2 MAX!

I saw over 16v when my regulator failed. My tach went crazy, the headlight bulbs burned out, and the wipers turned on by themselves while I was driving along!

My $.02, Cooper

[timmy2]

Originally Posted by Cooper911SC

The description you give is a classic sign of problems with a stuck voltage regulator overcharging your system.

Did you happen to notice a sulfur gas smell at the front of the car? Or inside the trunk?

The battery will die due to over charging, as all of the water gets boiled off.

I would replace the (now dead) battery with a new one, check the voltage at rest, should be about 13.2 volts fully charged new battery, start the car and check the voltage at idle and 2k rpm.

The regulator should limit the charge voltage to about 13.8 to 14.2 MAX!

I saw over 16v when my regulator failed. My tach went crazy, the headlight bulbs burned out, and the wipers turned on by themselves while I was driving along!

My $.02, Cooper

+1, my first thought as well, it's the battery drain when not running that is confusing. Maybe just an added bonus to a bad Alternator...

[1983Cabrio]

I did smell an odor coming thru the vent, just as everything went dim. I am now checking everything from the thread. Thanks for you advice guys! I know I'll find the draw.

[boyt911sc]

Originally Posted by DBDP

I would start by testing for a draw.

Remove the neg terminal from the battery and place a test light between the neg post and the neg battery harness. Make sure you have nothing on, including accessory lights, like door open...

If the test light is lit you have a draw. Start disconnecting harnesses when the light goes out you know your draw or short is in that harness. Slowly work your way down the harnesses until you pinpoint the location then dive into the electrical components.

I have used this method many times and have founds some silly stuff, like a seat cover that was pulling the power seat button up. The driver didn't notice because he rode with the seat in the highest location normally.

Hope this helps

I've used this method to locate my battery drain problem but used an ammeter instead of a TL. The mA reading gives you a better picture of how much current is drawn during the test. However, a lit TL is an obvious or direct indicator of a short in the system.

Tony

[1983Cabrio]

Ok. To sum up, it was the engine compartment light, it shorted out the system, blew the voltage regulator, that killed one cell in the battery. Whew. All fixed. Melted wires repaired, new regulator, battery. All good there now.