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Someone who has swapped in a LS motor Gen III 5.3 into 3100 truck have any suggestions on wiring harness to use. Hoping to find a stand alone using a 4L60E trans and drive by wire harness. Any help greatly appreciated....

Look through barnfind49 posts

Vettecrazy,

I put an 5.3 LS in my 51, 3100 but mine is a GEN IV with a 6L80E. I had the engine/trans stock wire harness trimmed by a vendor. So far so good.

I know this doesn’t answer your question but have you considered a GEN III salvage yard, stock harness to fit your application, that you could trim and keep the cable throttle? Is there an substantial advantage to the DBW accelerator?

I’m pretty sure barnfind49’s truck has the cable throttle and that he trimmed the harness himself.

I got the original harness...motor and trans but know nothing about trimming it down. Like to find some info about it. Thanks DB
Thanks K for tip on barnfind49

Take a look at lt1swap.com for good info. It isn't that hard, just somewhat tedious. Take your time and go one wire at a time and it will be done before you know it.

https://lt1swap.com/wiringharness.htm

People also refer to it as "dieting the harness" or "standalone harness".

I trimmed my own harness down. Mine is an early drive by cable engine. Would recommend looking at the aftermarket for a harness. If I ever do another swap I will not do the harness myself.

I'm in the middle of doing this research myself. There's a Facebook Group called LowBuck LS which has some good info in it. Recently a guy posted he does standalone harnesses. A drive by cable, 4L60e, Gen 3 harness was quoted at $270. Given how many hours I would likely spend dieting and extending OEM harness to fit where I wanted it, that sounds like money well spent to me.

I would recommend asking some questions like what kind of connectors he uses and what features are enabled (how many O2s, electric fans, a/c, etc). I have seen some really bad low-buck harnesses like that and they are a nightmare to deal with.

I used to take my time and remove ALL the extra unnecessary stuff and make it as “clean” as possible on harnesses I did for other people…… on my own truck i could careeeee lessss. I did a experiment to see how lazy i could be. Yes i use LT1 swap for my pinouts but I literally start at the red and blue connectors, de pin the junk not needed, cut them right off, taped them up individually then taped into harness to never be seen again, mark and chop off C2 connector and wire up a relay/fuse box with like 4-5 relays and fuses and boom….flash it start it drive it. Mines been flawless since day one and i never had to bother weeding out any of it or disturbing the harness any farther than the 2 connectors at ECU. Is it “hackish”? Sure mabey but when you de-pin the connector you essentially abandoned the wire….. no wires have power besides wires coming from the ecu so it’s totally safe. I think i built my harness in like 1 hour drinkin a beer and fired it up knowing it was good.

About to do another one on my new truck probably next week….but i dont think i can mention anything else about it on this site hahaha.

I went down the road of doing myself , after several hours I. Chose to purchase new from Howell Fuel injection . Matt Howell will call after you place the order and ask specific questions , Ecm location , single fan or dual , extended harness , etc. I chose to have the ecm harness extended 4’ and run out the rear of the engine so I can mount under the seat. I will be posting a
Build journal to share in the next few weeks , still in progress at this time .

This is interesting topic since I have swapped Vortec 5300 as well where is standalone harness but it is little mess now. There is several separate relays and fuse boxes. Main concern is that thick main harness root comes on top of engine. I do not think it could reach to glove box if I put PCM there. I have seen very neat installations where thick harness goes around the engine and is hidden there.

I've been looking into doing the same thing. The least expensive thing to do is do it yourself. The easiest thing to do as far as the frustration and headache factor, is to buy a pre-made one. There is certainly no lack of pre made harnesses on Ebay and Amazon, if you're brave enough to buy one. There are ones out there that are moderately priced like Karl Performance, Jegs, Speedway, and others, where at least you would have some sort of customer service. On the other hand there are complete kits from Holley, Fitech, and Edlebrock. Once you get over the sticker shock, they might not be that bad of a deal. Typically you're going to at least need the VATS deleted and custom tuning to deal with emissions controls, speedometer, etc... by the time you buy a HPtuners license and credits or even pay someone to do custom tuning, the Holley or Fitech option might not be that bad.

Probably going Holley...this thing making me old...LOL