Electrical 96 GT Electrical mystery

Sonare

New Member
Jun 28, 2019
2
0
1
49
Tennessee
Last year I got new battery at Autozone, and due to some corrosion got new terminals and some part of the positive battery cable at my local auto shop. My problems began some time after that.

The car would momentarily lose ALL electric power while driving. Loud pop in speakers, transmission would bump when power restored. Engine didn’t die. (Sometimes it was like a bucking horse when it would take a few seconds to straighten itself out. This was most often when car was first starting to drive, though sometimes in the middle of a longer trip.)
This happened randomly. There was never any evident pattern of circumstances to cause it to happen. It was sometimes often (daily, multiples times in one drive) and sometimes not again for several weeks. Many times the car would not start, it was as if there were no battery in the car. Dead as a doornail. Simply pull on the headlights and all was restored instantly and the car would start. I've dropped the car back there a time or two and at one other place, but no one found problems and/or it didn't act up while they had the car. Naturally!

One day recently I took the car to TireWorld after my little headlight trick failed to restore the power and I had to charge my battery a bit and jump it at home. They again replaced terminal ends to the battery and thought all may be well. I took the car and a day later got a battery light and high voltage on the dash gauge, though the car behaved fine. Next morning it was dead, and there was battery fluid sprayed all over the compartment. I jumped the car and drove it 10 minutes to TireWorld. Battery light was on again for a couple of minutes then went off. They jump started the car at one point, and when it started immediately the windshield wipers began to move and the pump sprayed lots of washer fluid on the windshield, and smoke began to come from under the dash. Shut it off quickly and disconnected battery. Later they diagnosed that the alternator went bad and cooked itself and my battery, and likely some wires/switches in the dash. Had car towed home to do some work myself.

Since then I have replaced the battery and alternator, have pulled out the headlight switch (no damage evident) and generally looked at what I can see under the dash and cant find any melted wires or anything. Once I connected the battery and started the car, I realized that numerous things weren’t working:

Speedometer

Rear Defrost light stays ON - cannot turn off - (I disconnected it for now)

Turn Signals (all but front right, which blinks fast. Left turn position just makes loud, hissing electrical noise, no blinking.

Hazard lights (lights on dash blink normally, but the exterior lights don’t)

Brake lights

Dome light

reading lights*

Clock*

Radio*
(aftermarket head unit connected to the stock MACH460 at BestBuy nine years ago. BTW, for years the right channel rarely works. Will come on at random.)
radio now comes on but I'm getting the same/similar electrical hissing from the speaker as I do from left turn signal.)

Door locks* (door button or remote)

*UPDATE: changed one blown 10 amp fuse under dash and now these work again. I also found one blown fuse in the high current fuse box (30amp) and replaced it. The rest seem good.

Before taking it to an auto-electric shop, what else could I do now? I'm no weekend mechanic and have no electrical meters of my own (my friendly neighbor likely does), but I can enjoy getting my sleeves rolled up and try some things. Thanks for any advice!
 
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wmburns

SN Certified Technician
Aug 14, 2009
5,849
505
204
Houston Texas
Does the high mounted 3rd brake lights work?

Confirm that fuse I/P #1 and #9 are good and have key on power in and out.

If looking for an educated guess, suspect a problem with ground G204 which is located behind the center console. This ground is shared by multiple devices including the GEM, radio, and cluster. Best to use a test light that will "load" the circuit.

Howto perform charging system voltage drop test
 

Sonare

New Member
Jun 28, 2019
2
0
1
49
Tennessee
Ok, I've spent a little more time on it again and here's where things are...
Replaced the burned out Right side outermost tail light bulb, so now I have right front and rear turn signals and right brake light functioning.
Still no left turn signal or brake light, or third brake light. All 6 tail light bulbs operate when parking/headlights turned on. The dash arrows light up and blink normally for turn signals and hazards but only right side exterior lights come on.

Along the way I have replaced turn signal flasher (turns out that was making the loud static and buzzing noise on left turns). I also changed the brake light on/off switch on the pedal, but that was a waste as I've since tested the old one and it was fine. I have borrowed a multimeter and checked for voltage in and out of the brake switch, and also the wires going into the multifunction switch. I also pulled that switch off and checked continuity (following a set of tests I found on another stangnet post) and everything seemed to check out. Next time I have time to work on it I guess I'll pull the front left turn signal bulb and check that, but even if it's burned out, that wouldn't explain the lack of the left rear brake light or third brake light, right? I would have gladly dropped it at a mechanic/shop by now but everyone's backed up with work. So is there anything else easy or obvious for me to try while I wait for a spot at the garage?

Oh, and I tried plugging the rear defrost switch back up but it still stays on so I pulled it out again. Does that mean I've got a wire shorted to power in there?

Thanks you.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,849
505
204
Houston Texas
I get the impression from your reply that your primary means of trouble shooting is by "parts changing". Performing testing only in a "limited" fashion.

I suspect that your failed alternator burned up SEVERAL things while it was producing excessively HIGH voltage. This is evident by the fact the battery vented fluid. This leads me to believe that your problem(s) likely has more than one failed parts. This means there isn't a single issue that if found can solve all of your problems.

I still suspect there's one or more grounds that have burned up. Unless you are willing to perform the detailed tests and post the results with the correct tool(test light) I have doubts I will be able to help you.

I'm willing to help you to trouble shoot each and ever problem but you have to be willing to perform ALL of the tests and post the results. But I'm not willing to write a "tome" regarding how to trouble shoot electrical if it's your intention to give up and go to a garage.

Good luck.