1990 k1500 5.3/4l60e ls swap wiring questions

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Biggun

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Justin
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1990
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K5 Blazer
Engine Size
350
Doing an ls swap with my blazer. I have a few questions to throw around to yall and double check my thinking. And I hope I’m posting it in the right place. I’m pulling the old 350 and tranny out now. Do I need to keep the original pcm and attached harness for any functions or can I rip it all out. I know the new computer runs everything for the motor and tranny. I’ve done a lot of searching and everyone talks about the new wiring but not what to do with the existing stuff. Also I asked this in the under construction part but then I found this and it seemed more fitting.
 

Camar068

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1986
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K10/LM7 5.3/4L60e/np208/3.73/32"
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10 yrs Air Force
I've thought about cleaning up what I don't need under the hood but haven't gotten around to it. If/when I do, I'll look at it one harness at a time and check all circuits on it to verify that I don't need it.

Could get tedious.
 

Camar068

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The cruise harness for example. It's still there with the vacuum line as well. I haven't removed it because I might be able to use it to hook up cruise instead of splicing into the blinker stalk connector.
 

Biggun

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That’s what I was thinking. I was hoping someone already knew instead of going through each thing.
 

Bextreme04

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It depends on a lot of things. The TBI computer doesn't do anything except run the engine in those trucks though as far as I know. If your 5.3 is DBW, you won't need anything from your original cruise except for the buttons on the stalk. If it is DBC you will also need the LS style cruise control module. None of the newer stuff uses vacuum for cruise at all.

Almost all of the engine wiring harness currently in your truck can go away. I would have to look at a wiring diagram of your truck to see what specific wires would need to stay, but it wont be many. Your LS swap harness will have everything you need for the engine/trans including the connection to the battery and starter wires. You then will need to connect the power feed to the rest of the truck from the starter. You will need an ignition power source to the ECU from the truck. Other than that it is almost all self contained.
 

Biggun

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Sweet thanks man. And I do have dbw. All things being equal if seemed like the simplest way to go with a few more advantages
 

Biggun

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I’ve got a couple more to throw out at y’all. My plan is to go with a stand-alone harness. I see a lot of people doing the custom deal but I don’t have the money for that. The harness of my 5.3 was sawzawed or I would go that route and diy it but there’s none local at all abs the ones on eBay are way too much then what if seen in the past few months. So if I get a stand-alone harness specific for my motor abs transmission will I have any problems hooking up my ac, abs cruise control. In some of the sites it gives the option to add cruise control with a custom harness Is this something that I can wire in myself at a later date after I’m on the road without having a new harness? I’m also going to throw in an efan with 2 fans off a 6.0 eventually and planned on getting the matching stockish radiator. Will the switches and all work into the pcm without adding that feature to the harness? I’m getting pretty far out of my 350 sbc comfort zone on this. Thanks!
 

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