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I've started to modify my stock 5.3 harness and followed all pinouts, I'm also running a non electronically controlled trans so I also took out all pins for trans too as shown on pinout from ltswap. I've come across a problem. As I was tracing wires down harness that I don't need, all the wires for trans plug are pinned out except for one, it's a gray wire and runs directly from trans plug to engine coolant temp sensor plug. What do I do with that gray wire? Do I cut it at trans plug and ground it directly?
Last edited by LunarNike; Oct 18, 2016 at 10:41 PM.
That lead is speed output for the auto trans. It has the same connector as the coolent. Both wires from the coolent connector go back to the ecu. On the 0411 and such C1-74=signal, C1-80= signal ground. Steve
Trucks have a few oddities in the harness. For some reason the low reference wire for the CTS and TFT are spliced together and share a pin on the PCM. Nothing wrong with it
That gray wire mentioned goes straight from trans plug to CTS, it does not go back up to a pin on the PCM. The question I have would be; Since I'm cutting off trans plug and cutting that gray wire would that cause any problems with the CTS? Being that it doesn't go back up to pin on PCM, it just goes straight from tans to CTS.
Neither the CTS or TFT function would work without going back to the PCM. You even pictured the splice pack. That wouldnt even be there if it was continuous A to B
Alright that makes sense, so the wire would then be on the Blue connector, pin 41? Don't recall that pin but I can double check when I get home.
thanks again!
Okay I've looked at the harness and its just a to b, gray wire straight from trans to cts but in the mess I think i followed the lt1swap pinout and might've taken out a pin, that connected to the splice pack as part of another sensor. I'm running a non electronic trans so I'm gonna cut off the trans plug so Theoretically could I just splice the gray ground sensor wire from the cts and put it in pin 41 on blue connector?
Alright sounds good I'll do that, I'm currently modifying harness. Anyone that has done this before what would you recommend for replacement loom? Any particular ones to stay away from and which diameters? How many feet of each? Thanks
There are four main types of loom, each with different pros and cons
1) Common split loom. You pulled a bunch of this off the harness from the start. Cheap, easy to use, harbor freight sells most of that you'd use. Beyond that youd need a bulk order which is far beyond what youd use for a single harness
2) High temp split loom. This is always black with white dots along its length. It resists up to 450* continuous and is useful around the starter area and anything close to the exhaust. Youll have to either re-purpose the old loom or buy large bulk. Its not something you'll be able to find a small length of
3) High flex split loom. This looks like braided flexible loom, but is split longways like common split loom. Its relatively expensive and difficult to work with compared to standard split loom, but can be installed at the end of the job. It is the most expensive type. Most aftermarket companies use this type for ease of installation if they use braided flex
4) Seamless braided flexloom. This is the real stuff and has to be installed over the harness as its built. It cannot be installed at the end, so construction time is nearly doubled. Its also difficult to work with as it must be cut with a heat knife and even then will fray easily. The ends must be capped with shrink tube or electrical tape. Often this is not heat resistant, so the act of shrinking tubing will melt the loom as well forcing you to start over. Long runs arent bad, but areas with multiple branches (injectors) are incredibly challenging. OTOH, it is the best looking loom and the harness retains nearly full flexibility in the end
How much of what size is fully dependent on your harness. If you stick to split loom, grab two packs of each size from harbor freight. Anything else, buy a harness kit from an online retailer. They should get you close
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Help with ls harness standalone 
