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L31 5.7 vortec swap help

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Old 12-04-17, 10:50 PM
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L31 5.7 vortec swap help

Ive got a 5.7 vortec and all the under hood gm harnesses and fuse box. I know that i can use the stock gm harness and get 12v to the 6 pink wires under run/start, and that i need 12v to the starter wiring during start and run as well and it will run. My question is, should i get the harness out of the gm truck that has the connecting fuse box under the dash for those wires or should i wire them into the harness of the rx7? Id like to use the fc harness, but id really appreciate some imput as to what wiring to get the 12v out of from the harness in the car? Thanks
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Old 12-05-17, 10:50 PM
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I don’t have any direct knowledge of FCs or the differences in GM harnesses. But I would probably skip using the GM fuse block and just grab the wires you identified and splice them into the RX7 harness. That’s will I plan on doing to my first gen and Ford EFI setup. After all, the engine just needs powers and gounds to run. Just be aware of the Mazda fuses current ratings so that you don’t overr draw from the Mazda circuit.
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Old 12-06-17, 07:06 AM
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Just run it standalone. Use the GM harness and modify it.

Im just finishing up my swap. Heres what I used.

You can get 12v Switched from IGN1 on the ignition switch.










Last edited by FührerTüner; 12-06-17 at 07:16 AM.
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Old 12-06-17, 07:13 AM
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This is where I plugged in my starter solenoid wire. Unplug the relay. Works good so far.


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Old 12-24-17, 12:38 PM
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Sorry for very late reply, but will i need any harness from the original fc underhood at all? I should be able to use the 5.7 harness to get the underdash fusebox power correct?
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Old 12-25-17, 08:08 AM
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The FC engine harness is unused. You can trash it except for the windshield wiper harness which is bundled in there. The body harness you will still use. You’ll need a new fuse box with relays for the fuel pump and fans. I pulled 12 constant and 12v switched from the steering column. My PCM is in the passenger footwell and I have a fuse block next to it.

I don’t have a relay block because I used fused relays for my fans and fuel pump instead.

Last edited by LargeOrangeFont; 12-25-17 at 08:11 AM.
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