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I left work, about 2 miles of city traffic then onto the freeway. While on thr freeway, only a few minutes, I noticed thr check engine light was blinking (which I know isn't good and i should stop). The car didn't sound or act funny in any way so I kept going, 15 miles or till I was home. Once off the freeway the car drove normal with not a single sign of a problem. The engine light blinking was also intermittent throughout the drive. When I got out of the car which was still running I heard a clicking/ rubbing sound coming from under the timing belt cover or that area of the motor. So I parked the car and went inside to eat. I came out later and started removing parts to get to the timing belt cover. Removed the upper cover and from what I could see things were visually okay. Checked the timing and that checked out good. Put everything back together and when I went to hook up the negative line on battery it sparked (big) and fused to the terminal in which I instantly whacked the cable free. Started testing fuses in both fuse boxes and didn't find anything strange there. If I put the #9 "Back Up" fuse out the voltage to the engine, tranny and ground strap is no longer there. I've been reading different forums and anything in-between and the closes thing I have found is possibly the "Multiplex Control Unit" maybe the culprit?

P.S. I hooked up my scanner when I first got home and that ended with no help because the scanner said "Link Error". I used a neighbors scanner as well and the sane results. Hopefully someone can give me a possible direction to go toward.

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  • It sounds from your description that the positive battery cable has worn in a spot and has grounded. I'd check it by feeling and sight all along it to see if you can find something wrong there. Oct 15, 2023 at 21:40
  • Positive voltage on the ground strap is perfectly normal if the ground strap is disconnected from the battery and your voltmeter probes are (+) to the ground strap and (-) to the negative battery terminal. You should read about +12 volts. In reality, you are connecting your (+) probe to the positive battery terminal through various loads in the car such as the the PCM and other modules, the clock, the dome light, radio, etc. Anything that it "always on" is a path of conduction between the ground strap and the positive battery terminal.
    – MTA
    Oct 15, 2023 at 21:58
  • With the ground strap disconnected from the battery, + probe to ground strap and - probe to negative terminal on battery, 12 volts is present which I understand when you say that it should be since certain items have constant power. When I hook up the ground strap to - terminal it sparks ( big, strong ) and fused/welded the cable end to the terminal which doesn't seem right. Should I just let it do what it is and continue to hook it up? Oct 16, 2023 at 8:45
  • @mattbmenifee This needs to be investigated carefully. Big, strong but momentary current can come from anything with capacitors in it such as a big thumping audio amplifier. Big, strong constant current is all wrong and could be dangerous. Best approach may be a carbon pile battery load tester between (-) and ground strap to check actual current. Lacking that, try a brake light bulb. If it lights up bright and stays on, you have a problem. If it flares for just a moment, it's safe to re-connect the ground strap.
    – MTA
    Oct 16, 2023 at 12:35
  • I have a break light bulb test light that I made. The power surges or flares until I hooked the alternator back up. Then the bulb got and stayed bright. Basically the voltage (10.30v-10.90v) to the ground strap no alternator hooked up to a solid (12.50v) with alternator hooked up. Oct 16, 2023 at 16:19

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This is a summary of findings derived from a dialog in comments.

To answer the question in your title, positive voltage on the ground strap is perfectly normal if the ground strap is disconnected from the battery and your voltmeter probes are (+) to the ground strap and (-) to the negative battery terminal. You should read about +12 volts. In reality, you are connecting your (+) probe to the positive battery terminal through various loads in the car such as the the PCM and other modules, the clock, the dome light, radio, etc. Anything that it "always on" is a path of conduction between the ground strap and the positive battery terminal.

It is likely that your alternator was producing an invalid output, perhaps an AC voltage superimposed on a DC voltage due to the failure of a diode in the alternator, which caused all kinds of havoc in your car's electronics.

You disconnected the battery before investigating the noise in the timing belt area, which proved inconclusive, but when you reconnected the negative battery cable, there was a big spark and a heavy current so you disconnected it quickly. It is likely that re-connecting the battery prompted one or more diodes in the alternator to transition from "flaky" to "dead short".

By using a test light, you proved that the heavy current drain was attributed to the alternator, so you took the alternator to a parts store for testing. The store was unable to test the alternator, so you purchased a replacement alternator and installed it. That seems to have fixed the problem.

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