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It wasn't an insult...fb...Facebook.
How should I go about making a custom wiring harness for a 5.3 LM7 swap?
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I think the trick is to remember that every truck will be different. You need to get super familiar with the wiring diagrams for your specific truck, and the specific motor you're dropping in it.
If you're doing a stand alone, remember that you've got essentially two different harnesses- one for running the engine and one for running the cab. You can use the diagrams at lt1swap.com to figure out what you can thin out, what you don't need from the pcm and engine harness. But only you can figure out what it is you want to keep on the body harness.
Every accessory you want to keep complicates the integration of the two. It was simpler for my setup because I only needed to keep gauges. It was a carbed truck without ac and a manual fan.
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16,856 Posts
By the time I finished my harness, besides having both FSM's, I had close to 50 pages of specific section diagrams I downloaded. W/o them it'd be tough to get it all right. mine was just the opposite. I kept the A/C, cruise, DBW, evap, TBSI, Vats, etc. And upgraded the PCM to an 04 P59.
I think if I were to do it again I'd first swap the truck to an 01-02 0411 while the 4.3 was still in it. Get all the bugs worked out of that. Then add what was needed for the LS coils, injectors, and DBW.
I think if I were to do it again I'd first swap the truck to an 01-02 0411 while the 4.3 was still in it. Get all the bugs worked out of that. Then add what was needed for the LS coils, injectors, and DBW.
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The advantage you had was being a 40 GM tech. That wasn't ask option for us, even though Harley is a wiring King. This swap was going on right at the height of covid, and we needed to get this wrapped up.
Kudos to those that have the ability and time to make their own. It just wasn't an option for me.
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1,076 Posts
I've had too many failures of existing harnesses/connectors in their original vehicles to make me ever want to work on one.
Wanna know what heat cycles and electrical current running through wiring does to the wires? Just compare the two - work with an existing harness for a few minutes, then switch to a new one. Wires are stiff as hell in a well used harness where they're pliable in new. Connectors are crimped pins, not soldered, and will break as will the plastic plugs.
Mediocretes Service and Occasional Repair, my shop, is a perfect example of why to opt for new first. After you've wasted the countless hours finding your way through wiring diagrams and building one, you get to troubleshoot why it won't work. Finally, throw up your hands, give in and order a new one that works flawlessly. I'll dig nickels out of ashtrays and couch cushions until I can afford a new harness, I'm not wasting my time on something that will fail, more likely than not.
The motto of Mediocretes Service and Occasional Repair covers this nicely: "We do it right because we do everything twice!"
Wanna know what heat cycles and electrical current running through wiring does to the wires? Just compare the two - work with an existing harness for a few minutes, then switch to a new one. Wires are stiff as hell in a well used harness where they're pliable in new. Connectors are crimped pins, not soldered, and will break as will the plastic plugs.
Mediocretes Service and Occasional Repair, my shop, is a perfect example of why to opt for new first. After you've wasted the countless hours finding your way through wiring diagrams and building one, you get to troubleshoot why it won't work. Finally, throw up your hands, give in and order a new one that works flawlessly. I'll dig nickels out of ashtrays and couch cushions until I can afford a new harness, I'm not wasting my time on something that will fail, more likely than not.
The motto of Mediocretes Service and Occasional Repair covers this nicely: "We do it right because we do everything twice!"
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16,856 Posts
The trick to building your own harness from scratch is to do one wire at a time. Figure out where it comes from and where it goes and the best routing to get it there. You'll need a large selection of pins for the computer end and weatherpack terminal parts and the special crimping pliers. Or do a lot of soldering on of old terminals with some wire attached.
Problem is there are literally hundreds of wires. Took me a month and I'm seriously thinking about redoing it from scratch because I don't like how it looks. Everything worked on the first try, but it's a bit cluttered looking under the hood. I want that almost no wires showing look, but there's an art to doing that which I've never mastered.
Maybe I should take it to Martin Brothers or Kindig-It Design and give them a blank check. I did catch one episode where they were having trouble running part of the wiring inside the frame rails. On an S10 there is also a lot of room between the inner and outer fenders at the top.
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Maybe I should take it to Martin Brothers or Kindig-It Design and give them a blank check. I did catch one episode where they were having trouble running part of the wiring inside the frame rails. On an S10 there is also a lot of room between the inner and outer fenders at the top.
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Depends on what you're running. If you have changed the trans or A/C style you have to have a custom one made. IIRC in Rhot's case they were using a later computer in a 96.
I've also been led to believe if you have 4wd you have to wire that stuff yourself since they won't include any transfer case or TCCM wiring.
I've also been led to believe if you have 4wd you have to wire that stuff yourself since they won't include any transfer case or TCCM wiring.
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35,595 Posts
P59 ECM...CPW did tell us that the ABS wouldn't work, so we replaced the bread box sized ABS with one from a 2000, along with a M/C and 8" brake booster. The smaller booster was needed to clear the fuel rail covers. ABS works fine, as does all of the gauges.
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The link to photobucket said Oops 404
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My harness included a 4x4 two wire connector. It was up by the 16 pin connector that is close to the evaporator box/PCM. I have no clue what it is for. This leads me to believe CPW makes a standard S10 style swap harness and adds in what specific changes are requested by the customer. Mine also had a flex fuel connector and I never spoke of using the flex fuel sensor. I have that tucked over by the brake booster under the cruise/pedal sensor.
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2,235 Posts
I chose to build my harness 1. because it was fun for me, and 2. I was able to route the wires how I wanted, so they were as hidden as possible. It was many hours of work stripping the old harnesses I had down to each circuit and reassembling one circuit at a time, but the results were perfect and it started on the first try. You can do it if you are dedicated, want to learn and have the patience. The CPW harness is a great option from what I've read, and I would have taken that route had I not wanted to make a harness.
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Word of caution demonizing a specific Mfg. Be sure your legal advisor says you have evidence to win possible suit that could result. Wouldn't be pleasant to face the same problem that several now do in demonizing Vote Machine Manufacturers.
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