brown wire from alternator plug to regulator plug fried, why

[jerry]

i have recently had trouble with my starter motor barely turning over just enough to start the car. i think it was a coincidence that this issue started after i did a compression test and discovered that i had 175psi across all four cylinders. i have a new starter too. anyhow, my battery measures 12.6V at the terminal. when the car is running, the voltage between the thick red wire at the back of the alternator and ground was 13.5V which is the lower limit of acceptable.

upon closer inspection, i saw that the brown wire from the 3-wire plug on the back of the alternator had melted the insulation.

This is a new discovery that was not there when i rehabbed the wiring harness. i have seen this happen on several other harnesses.

what causes this? i suspect that it may be due to increased resistance from corroded wires. the spade connection did look a little oxidized.

as a short time fix to get me going i merely re-ran a wire from the alt to the regulator, until i can do a proper replacement inside the sleeve.

i also discovered that my alternator light in the instrument cluster was dead so i had no dummy light to indicate pending doom. that's fixed now and seems to function normally now.

anyhow, i guess i'm concerned with the underlying cause of the fried wire at this point and whether or not my car will start tomorrow morning so i can go to work on time...

[gracer]

Check you engine to frame/battery ground strap. G

[AceAndrew]

Check you engine to frame/battery ground strap. G

As well as the alternator to block ground (is the long skinny alternator case bolt to which the ground wire attached discolored in any way?). I recently went through this exact same thing (slow starting...eventually led to no starting) and ended setting fire to my wiring harness, not very fun. Check the regulator and see if it's fried as well.

[Guest_anonymous]

+1 bad ground.

torched my harness from the alt to the firewall. temp sensor, starter, alt mini harness grounded to frame rail due to bad ground at alternator.

[jerry]

thanks for the replies.

i will recheck both those grounds tomorrow. i do know that i made my own ground wire out of a thick brown-skinned wire i had for use between the engine block and the body.

the other shorter wire between the alt and timing cover uses an OEM piece.

is there any checks with a voltmeter i can verify correct connections on these? sounds like i may not be getting enough grounding between engine block and body and it's shorting on the smaller brown wire...

i'll look for discoloration.

[jerry]

i installed a thicker ground wire between engine and frame rail. starter is back to normal. lesson learned. thanks