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RTs83LSX

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May 25, 2024
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Hey peeps, I'm RT and I have an '83 MC restomod that I have been working on since 2020. This is my first (and last) restomod and I'm at the point where everyone seems to struggle and that's the wiring harnesses. I have done a ton of research and purchased a custom Engine Harness through BP automotive. After many months of research and reading online and reaching out to aftermarket companies, I purchased a universal wiring harness for inside the car through American Autowire. I have an WS6 LS1, 4L65e, complete Vintage air kit, Autometer gauge cluster, and everything is new but the wiring is intimidating but I feel like I'm a pretty smart guy so I should be able to figure out this wiring thing. All the old wiring is out so it should be simple to get started, but I don't even know where to start and I don't want to make a mistake along the way. Any advice is welcome. Thanks
 

doood

Amateur Mechanic
Sep 24, 2020
620
862
93
Hey peeps, I'm RT and I have an '83 MC restomod that I have been working on since 2020. This is my first (and last) restomod and I'm at the point where everyone seems to struggle and that's the wiring harnesses. I have done a ton of research and purchased a custom Engine Harness through BP automotive. After many months of research and reading online and reaching out to aftermarket companies, I purchased a universal wiring harness for inside the car through American Autowire. I have an WS6 LS1, 4L65e, complete Vintage air kit, Autometer gauge cluster, and everything is new but the wiring is intimidating but I feel like I'm a pretty smart guy so I should be able to figure out this wiring thing. All the old wiring is out so it should be simple to get started, but I don't even know where to start and I don't want to make a mistake along the way. Any advice is welcome. Thanks
I would keep all the LS1/4L65e wiring in the engine bay and spend a bit of time and effort to get the ECU connections reasonably weatherproof. PSI conversions or Holley will tell you to put the computer in the cabin. My mistake was putting the ECU in the dash. I sacrificed the glove box and stock ECU still doesn't fit right. It also pinches the cables for the heat only HVAC, and messed up damper actuation so I only get heat in defrost on the windshield. I'll get in there and figure it out one day, but its been 2 years. I fed the LS1 and fan harness through the passenger firewall hole behind the inner fender (where CCC computer harness went). You can bring anything you need for the instrument cluster through the speedometer cable firewall penetration next to the brake booster. I have an oil pressure sender coming through that penetration. I used the stock starting circuit; I should have put a relay to not start without brake depressed. I used the distributor pink wire for something, but left most of the factory wiring abandoned in place. I put four strands of 10 gauge wire down the factory fuel hard line with zip ties all the way to come up into the trunk; single fuel pump currently uses one strand and grounds to the body (was a carb car). Since I have the interior out of the Oldsmobile I will put that under the carpet next time.

TLDR. Leave as much of the factory wiring abandoned in place as you can; put all the swap wiring under the hood and use the penetration for the speedometer cable for anything you need to bring into the dash. It is very easy to take the CCC harness out and that gives you another penetration; reuse the Grommet
 
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SS_Malibu

Royal Smart Person
Supporting Member
Sep 27, 2021
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If it were me, I would start by laying the two wiring harnesses out on the ground and mocking it up as if it were in the car then label the connections. I would make sure they will connect with each other. Once everything is labeled you will know where things go and what you may still need to complete your harness and any extra connections you may have that won't be used. I wouldn't cut anything extra as you may want to use it in the future. Start laying the harness in the car. Be sure to pay attention to detail and Take Your Time. Good Luck.
 
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mclellan83

Comic Book Super Hero
Jun 27, 2017
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Welcome, you cant tease us like that and not show any pics of the progress. Hahaha. I understand completely how the wiring can be intimidating, I would do like SS says and lay it out all mocked up and while I wouldn't cut the wires I would see if I could depin what you aren't using to cut down on the amount of wire there so it is less overwhelming
 
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doood

Amateur Mechanic
Sep 24, 2020
620
862
93
Welcome, you cant tease us like that and not show any pics of the progress. Hahaha. I understand completely how the wiring can be intimidating, I would do like SS says and lay it out all mocked up and while I wouldn't cut the wires I would see if I could depin what you aren't using to cut down on the amount of wire there so it is less overwhelming
sounds like he has an aftermarket harness. Should be loomed and not have too many degrees of freedom. I'd throw it in the engine bay (assuming engine/manifolds/trans present) for mock-up without connecting it. Aftermarket harness is plug and play.
 
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