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Jump cables got crossed on my 89 Volvo 740 turbo intercooler... What all needs replacing?

etduncan

Member
Joined
Jun 1, 2023
My friend was giving me a jump because my car has some sort of power leak, so the battery dies if I forget to take off the battery ground. The jump went well and the car fired up, so I opened the trunk to put away the leads, while he took them off, and the car died. I asked him what happened and saw he had crossed the leads together. I was able to start the car while it was back connected to his battery, but the electrical for the car (Lights, gauges, everything except the radio for some reason) didn't work. it also is only part of the time responsive to the gas pedal, drives rough as hell, and lurches. When I stopped it it immediately died. I can still get the electrical systems (Lights, radio, gauges, etc) to work while I have the key in, but if I try to start it, they all shut off, and the starter isn't trying. I'm guessing the ECU is fried, ordered a new one... Is there anything else that will need replacing?
 
Might as well start by checking the fuses.

When you say "he crossed the leads" - do you mean he somehow hooked them up in reverse while your car was running (+ to - and - to +) or that he shorted them together while removing them?

If your alternator was working, seems weird that connecting things backwards would kill only one car - but I could see maybe killing the battery by dead shorting it?
 
Might as well start by checking the fuses.

When you say "he crossed the leads" - do you mean he somehow hooked them up in reverse while your car was running (+ to - and - to +) or that he shorted them together while removing them?

If your alternator was working, seems weird that connecting things backwards would kill only one car - but I could see maybe killing the battery by dead shorting it?
He shorted the system while removing them, when he disconnected the leads from the other car he clamped them together
 
Sounds like it killed the alternator, there was barely enough battery voltage to keep the fuel pump and ignition running for a short time.
Would that make all electrical shut off whenever the car attempts to start? I could see that
 
the alternator seems to be bad, surprisingly the battery doesn't seem too bad, holding a steady 12.6 volts
 
Fully charge the battery and try running your car again. Most likely the alternator was damaged and isn’t charging. That may be all that was damaged. Electronic fuel injected cars do not run well at low voltage.
when the battery is fully charged, when I attempt to start the car should it just shut off if the alternator is gone?
 
If the alternator is bad, it may be draining the battery, or may be so bad that it prevents the car from running. You should be able to disconnect the alternator completely (wrap each disconnected wire in electrical tape to prevent shorting), and run on just the battery for a while.
 
Tested out the alternator, and I'm getting nothing from it. ordered a new one, as well as a new fuel pump relay because it had burn marks on it, which doesn't seem particularly good to me.
 
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