mk3 electrical issues

limitedgt4

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hi all,

i have had my supra for some time and done a'lot of work to it but recently i did something, which i cant figure out, and it has giving me some electrical problems. to start, the car ran fine, started instantly without any issues. after installing a mishimoto electric fan switch, the car didn't turn on. at this point, the dome light and door lights and everything turned on the car and it cranked but no power to the fuel pump. the fuel pump is a walboro with the fuel pump relay mod, relay is in the back hatch and has been running like this for this for some time. i checked all wires going to the relay and what I found was that the ground wire , somehow was not grounding properly, if i used ground wire from the battery directly, then, it worked and then the car would start fine.
then i remembered that when the tail lights were bad the car would not start so i checked the light bulbs and replaced the ones that were bad and that "solved" the ground issue. by mistake, i left the ground wire from the battery to the hatch and when i tried to start the car i heard a clicking noise and then lost all power, not even the door lights or dome lights would come on . i have checked all the fuses and all the relays in the the fuse box and in the drivers side fuse panel. i have tested the relays and after removing and testing and reinserting, the car regains power to the to the door lights and dome lights, however after regaining power every time i try to restart the car i hear the same clicking noise and once again i lost all power in the car.
each time i reset the relays and fuses, i regain power in the car but when i try to start it, i lose all power until i reset all of the fuses and relays. it is a baffling situations for me. what could cause the car to lose all electrical power?
i have considered fuses and relays in the fuse box and the in the drivers side panel, what else should i be looking for that could cause this behavior.


p.s. i have disconnected the mishimoto fan switch and the problem is still there.
 

limitedgt4

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Sounds like maybe a loose main body ground? How are all your grounds?

wouldnt be surprised if it was, but i have checked, removed, scraped and secured all of the grounds. it seems more like a breaker/relay trips and once reset the power is restored but something is causing it to trip each time. would a bad starter or bad alternator cause this? its like something in the car is drawing more current than its supposed to and causes a trip. if i disconnect the negative terminal for a minute or two and reattach it, then the power is restored until i try to start the car again and lose all power.

would a bad starter or alternator cause such behavior?
 

hvyman

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Check the little wire on the battery
 

figgie

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wouldnt be surprised if it was, but i have checked, removed, scraped and secured all of the grounds. it seems more like a breaker/relay trips and once reset the power is restored but something is causing it to trip each time. would a bad starter or bad alternator cause this? its like something in the car is drawing more current than its supposed to and causes a trip. if i disconnect the negative terminal for a minute or two and reattach it, then the power is restored until i try to start the car again and lose all power.

would a bad starter or alternator cause such behavior?
It depends

i have done some testing with the starter,

Just the starter solenoid itself pulls a whopping 32 Amps steady state. The starter motor pulls 92 Amps sustained, that does not include the initial inrush of juice which is usually 3 times the steady state amount.

if it was the starter relay, that starter solenoid would be blazing hot.

I would look at the grounding from the battery to see if there is any wire that is missing or worse, that has had insulation melted off.
 

Piratetip

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When I datalogged a few cranking events the total sustained cranking amperage was about 150A.
So your numbers look pretty good to me figgie, maybe just a hair low.


Peak starter inrush is around 500A.
 

figgie

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When I datalogged a few cranking events the total sustained cranking amperage was about 150A.
So your numbers look pretty good to me figgie, maybe just a hair low.


Peak starter inrush is around 500A.

I did my calc based on a 1.2kw starter motor and 13vdc. I probably should have done it at 11vdc.

the starter soleniod i was able to get a direct amperage measurement from my Power supply. :) ( which was at 12.4 vdc)
 
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limitedgt4

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Hi all,

thanks for the input. more than anything i think i just needed some emotional support and some ideas. i was able to track down the problem and it did turn out to be a ground issue :eek::eek::eek::eek::eek::eek:. it was the main ground wire was not making enough contact with the unpainted surface area on the terminal that goes to the battery. a nice wire wheel and 20-30 seconds of removing all the paint on the terminal and presto, no more issues. im actually surprised the car ever turned on before i removed the paint from the terminals.