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Ted Ritter
Ted Ritter, Toyota Master Tech
Category: Toyota
Satisfied Customers: 4361
Experience:  Toyota Master Tech, ASE Certified
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1990 Toyota 4Runner SR5 with a 1991 3.0 3VZ. When I got it,

Customer Question

1990 Toyota 4Runner SR5 with a 1991 3.0 3VZ. When I got it, the alternator had a terrible short. Was able to resolve that. Now, each time I turn on the ignition, the ECU and EFI fuses blow immediately. What is causing this?
Submitted: 10 months ago.
Category: Toyota
Expert:  Ted Ritter replied 10 months ago.

Hello, thanks for posting

You said "when I got it" do you mean that you just bought this truck in this condition?

When the large alternator wire shorted there are some other wires in that same harness that are probably also shorted together inside the harness.

Customer: replied 10 months ago.
I purchased the vehicle in this condition. Too good of deal to say no to. Where does that harness go and how difficult is it to replace?
Expert:  Ted Ritter replied 10 months ago.

It's part of the engine main harness so it would be best to open the insulation and check for burned wires, , just race the old alternator wire where it enters the harness then open tre insulation and check the wires. I'm going to look at a wire routing diagram and see if I can upload something a little more specific.

Expert:  Ted Ritter replied 10 months ago.

9b444505-de37-454b-989c-ebce14630889_componen.pdf

Click on this link or copy it into your browser, note the connector G1 is for the alternator.

Customer: replied 10 months ago.
Will it be easier to trace for the short or to replace the entire harness?
Expert:  Ted Ritter replied 10 months ago.

The harness is going to be expensive even if you can find one at a dealer or maybe a used one and very time consuming to replace, personally I would try to find the short, one thing you can do is to disconnect various components and see when the short goes away, related would be the fuel injector wiring , fuel pump, air flow meter and just about anything else that has an electrical connector on it under the hood.

Customer: replied 10 months ago.
Okay. Spent some time trying to trace the wires back and although the diagrams are helping, I still cant see exactly where the alternator wires go.If I disconnect the starter, the short still exists. Am I correct by assuming the major short is between the alternator and the starter? If so, how exactly do those connect to each other?
Expert:  Ted Ritter replied 10 months ago.

The large alternator wire gets power from the 80A alternator fuse in the box under the hood, I'll send you a wire diagram(schematic) in a few minutes.

Expert:  Ted Ritter replied 10 months ago.

157d9250-e190-4bc6-9673-a079124c53fa_charging.pdf

Customer: replied 9 months ago.
Still having trouble seeing where those wires go and where they might be shorting out with others like the efi and ecu. Does the alternator wire go through the starter or not?
Expert:  Ted Ritter replied 9 months ago.

No, it does not, it's connected to the 80A fuse in the fuse box via the large white wire, It is enclosed in a harness with other wires, The only wires going to the starter are the heavy cable from the positive battery post and the solenoid wire from the ignition switch which goes through the starter relay and the neutral start or clutch switch depending on which transmission, before going to the starter. Looking at the wire routing diagram it looks like the alternator wire goes to the harness that goes over to the coil/igniter, could be a problem there which would make sense since those fuses blow.

These kinds of short circuits take time to find, what I'd like to suggest is to remove the EFI fuse and with the key on connect a 12 volt test light directly across the two terminals, the light should light up due to the short, then disconnect things related to the ignition system and the EFI system, one at a time and note if and when the light goes off, at that point you have found the circuit causing the problem

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