LS swap Gurus

[jon316]

Hey guys I have a 81 c10 that I got halfway(more like 1/4 way) done. So it’s just been a mess of figuring out what’s what. So I found the stock harness for the truck bundled up on drivers side fender. Should o just get rid of most of this? I found what goes to the lights. But still so many wires. Found two red wires which I assume are power to fuse box. But the rest I have no clue and wiring schematics are just no help to me. Any tips?






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[bd]

Every wire has a beginning point (source) and an ending point (destination).  The wiring diagram is just a map showing the connections between those beginning and ending points.  Each line on the diagram represents a single wire.  The lines are generally straight, making occasional 90° turns.  The lines on the diagram are labeled at the source and destination points using the metric equivalent wire gauge, wire color, and circuit number for the wire each line represents.  The metric wire size is converted to the equivalent American wire gauge (AWG) using a table that is included as a prefix to the wiring diagram(s).  For example, .8 BLK-150 is a 0.8 (mm)² black wire in circuit number 150.  Using the conversion table included with the wiring diagram, .8 (mm)² is equivalent to 18 gauge.  Circuit 150 is GM's standard callout for ground wiring. 

Sometimes the type of wire insulation used in a specific application is called out on the wiring diagram, too.  For example, 3 PPL-6(SXL) is a 3 (mm)² purple wire in circuit number 6 (starter solenoid) that is jacketed with SXL wire insulation.  Using the conversion table, 3 (mm)² is equivalent to 12 gauge.  Type SXL insulation exhibits superior heat, chemical and abrasion tolerances that are preferable attributes for wires bearing the high heat environment in the vicinity of the starter, which is in very close proximity to the exhaust.  For a successful undertaking such as a swap, you need to become familiar and confident with interpreting wire diagrams.  The trick is to follow one wire at a time from its inception point to its destination point.  Learning may seem tedious at first but will become easier with practice.  There is plenty of assistance available on this forum to help you understand the diagrams.

Wiring that has been hacked and cobbled together will need to be separated so that each wire can be followed to its source point.  Clear images of the wires in question as they enter the firewall bulkhead connector will benefit accuracy.

[jon316]

Fantastic thank you! Just wanted a starting point of where to head to first. Some of the wiring was chopped and got different color wiring but that’s a few I can chase.

Appreciate it!!


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[jon316]

So technically the junction block behind the motor had the alternator, ignition(solenoid) connected to one post and the other to the battery or ac box? Is it ok to run it like that again? I don’t have the factory 5.3 junction that sits next to the alternator unfortunately.




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[jw fatboy]

Have completed a few re wires on this gen truck and I can give you a few tips on the original wiring.   The 3 tools you will absolutly get more use out of than you can imagine are as follows.   1 volt ohm meter,  1 set of 10 ft expandable jumpers, 1 - 12 volt doorbell.  I am working by myself most the time so the bell will save a bunch of guess work and moving around.  Chiltons have good schematics and are very easy to read.  Cutting and splicing is not an issue when needed, if done properly.  Option 1 being solder joints and option 2 being butt slices.   Both splices are covered with heat shrink for insulation.    All butt splices are completed with the use of dialectric grease coating the bare wire before crimping.   I have butt splices on trailer wiring that is over 20 yrs old and never had an issue.   Keep the wire size the same size when making a splice.   If you don't have a proper color, number the wire and note it on schematic.  1 thing to remember when tracing the wires is a few of the circuits use the ground as the switch leg, (IE) horn, some windshield washer pumps. ect.  If you have any questions feel free to reach out.

[jon316]

Hey guys back again, didn’t want to start another thread. Waiting on some wiring parts to get started on those gauges and all that wiring. But mean time I just plumbed up all the fuel and etc so wanted to turn the engine over and get it started.

Now I started but running the negative cable to the body(should I run it to the engine instead?) and the power wire that came with the engine to the starter straight to the battery. My idea was run the power to the starter, then power the ecm etc which I ran wires for then run the wire for the solenoid and tap it on the positive to get her turning. But it all went wrong on step one. I put the positive cable on battery and it was good then the ground, and I heard sparks and saw smoke and wire got real hot quick so I pulled it out. Figured maybe the starter was shorted or the solenoid was stuck. So I removed the positive left the ground on and hit the solenoid. Solenoid ticks.... so what’s going on here. How the heck is the starter shorting out is it really bad? I’ve seen plenty bad starters but never seen them short out. I had tried one more time moving the wire around and my steering box started to smoke once I put the positive cable back on. Weird!!







Doesn’t seem to be touching anything that I know of.



Clearly shorting lol!


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[jon316]

Went and tested starter, had to go to 4 different auto part stores because their machines were “broken”. But starter checks out. I’m thinking it’s a grounding issue. So I ordered some ground wire. Gonna ground to engine, frame and body. Hopefully that solves my issue. Probably change that old positive cable as well.


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[bd]

The negative (ground) cable from the battery should connect directly to clean, bare metal on the engine block.  There should be a 5/16" braided copper strap (or ~10-gauge wire) connecting the engine block to the cab firewall to effectively ground the cab.  It also should have a redundant 10-gauge ground wire connecting the right frame rail directly to the battery's negative post.

If the steering gear was smoking, the starter was attempting to ground through the steering gear.  Inspect the B+ cable very carefully for adequate clearance to any possible ground contact.  Was any other wiring connected to the battery when the arcing/smoking occurred?

The B+ (battery positive) cable from the battery connects to the starter solenoid 3/8" (10mm) stud as shown in the image you posted.

[jon316]

Thanks!!! Just ran some make shift grounding wire I had laying around to see and low and behold that was it. Got her started she purrs like a kitten


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[jon316]

Been starting on the gauges. Seems the more I dig into this thing the more mess of wires I find!! Hard to pull up diagrams when there’s house butt connectors on things and wires cut and tapped. Holy cow!


This one I have no clue what it is?


This one I am gonna assume it for the radio as the wires on the right hook up to it but holy heck the mess on the left I have no clue what it does.


Since it connects to these three wires, definitely has me baffled.


These blue wires tie into the front lights harness? That’s not stock right it looks to be squeezed on the side of the grommet.


And for the brake switch, which one am I supposed to use? I know on the ecm there’s two one for brake and one that needs power all the time unless brake is pressed to disengage the TC. I’m gonna assume it’s the black?


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[bd]

^^^^ factory radio speaker harness




^^^^ more radio wires butchered by a shade tree installer
(Note: the white connector and switch with light blue and pink/black wires at the top-center of the image are for the torque converter clutch (TCC))




^^^^ orange = fused B+ for brake lamp power; white = brake lamp feed into turn signal switch; the dark green and black wires in the adjacent connector are for the cruise control




^^^^ trace it

[jon316]

Greatly appreciated! So that blue plug is supposed to be plugged to that big connector with the bunch of wires? Or is there another separate harness for radio too. Think I’m just gonna rip it all out and run new speaker wire and etc.

Thanks for noting the torque converter plug! Didn’t even know it has that there. So those two wires will be plugged to the new harness? Happen to know which is direct constant feed and which is power when brake is pressed?


I thought the three wires to the left (black blue brown) were for the cruise control. Believes my new harness has three wires, do I have to tap into that AND the brake switch as you mentioned above? Be awesome to retain cruise control on the new swap!


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[jon316]

Another I been trying to figure out is the one for the solenoid. You mentioned it being this one but shouldn’t it be smaller one, although their is a lot of wires tapped together there. I’m super confused on what wire starts, what charges the battery, what goes to the post and what shouldn’t.

Sorry my electricity knowledge of very minimal and considering my grounding issue almost lit my gearbox on fire I’m trying to be very careful!


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[bd]

^^^^ That large black socket is supposed to be used to adapt the factory radio wiring to an aftermarket radio pigtail on a plug-n-play basis in order to avoid hacking up the original wiring.  It doesn't appear the installer made the connection (pun intended).  The siamese blk/blu/brn wires come from the column-mounted cruise control engagement switch.  See page 8C-73, Fig. 8C-61 of the 1981 Service Manual.


The "B+ post" of the starter solenoid is the 10 mm stud to which the positive battery cable connects.  The 10 mm ring terminal with the two fusible links displayed in the annotated image connects to the B+ post of the starter solenoid (see below).  The pair of fusible links protect the two 12-gauge red wires that feed power to the firewall junction block and into the cab.  The factory wire that connects the crank circuit from the ignition switch to the "S terminal" of the solenoid should be purple in color.

[jon316]

Great thank you! I’ll be tracing that purple wire today then. Also run that wire to the starter see if I can can trace it back to the junction block and see if I can get everything powered up.  Appreciate it!


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