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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => LT/LS Swaps => Topic started by: jon316 on March 07, 2020, 03:17:36 PM

Title: LS swap Gurus
Post by: jon316 on March 07, 2020, 03:17:36 PM
Hey guys I have a 81 c10 that I got halfway(more like 1/4 way) done. So itís just been a mess of figuring out whatís 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?

(https://uploads.tapatalk-cdn.com/20200307/5e1f3b3808f29b8fb5c85da12a9c776f.jpg)(https://uploads.tapatalk-cdn.com/20200307/b8c4fef8c8cad321c47a4c624d6a312c.jpg)(https://uploads.tapatalk-cdn.com/20200307/de72208c3684e27028a88e3417e3f4cc.jpg)(https://uploads.tapatalk-cdn.com/20200307/b6755ed11756477a7ea584123d70db37.jpg)(https://uploads.tapatalk-cdn.com/20200307/0c10fa474f43670379c4f99234f28a11.jpg)(https://uploads.tapatalk-cdn.com/20200307/73f69714d6233e6e727d67ae10aa7550.jpg)




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Title: Re: LS swap Gurus
Post by: bd on March 08, 2020, 01:21:04 PM
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 90į 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.

Title: Re: LS swap Gurus
Post by: jon316 on March 08, 2020, 01:53:35 PM
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 thatís a few I can chase.

Appreciate it!!


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Title: Re: LS swap Gurus
Post by: jon316 on March 08, 2020, 03:23:11 PM
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 donít have the factory 5.3 junction that sits next to the alternator unfortunately.

(https://uploads.tapatalk-cdn.com/20200308/b65edaec4fe422132169f0bd882f80f5.jpg)


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Title: Re: LS swap Gurus
Post by: jw fatboy on March 09, 2020, 07:13:22 AM
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.
Title: Re: LS swap Gurus
Post by: jon316 on March 23, 2020, 12:47:09 PM
Hey guys back again, didnít 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 whatís going on here. How the heck is the starter shorting out is it really bad? Iíve 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!!

(https://uploads.tapatalk-cdn.com/20200323/0f098e5cb2071b5f32b5d6fb8d538052.jpg)


(https://uploads.tapatalk-cdn.com/20200323/b06963772c199584e96a47f15cf9528f.jpg)


Doesnít seem to be touching anything that I know of.

(https://uploads.tapatalk-cdn.com/20200323/124052160da6639d6707e37051475bfe.jpg)

Clearly shorting lol!


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Title: Re: LS swap Gurus
Post by: jon316 on March 23, 2020, 01:55:39 PM
Went and tested starter, had to go to 4 different auto part stores because their machines were ďbrokenĒ. But starter checks out. Iím thinking itís 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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Title: Re: LS swap Gurus
Post by: bd on March 23, 2020, 02:28:01 PM
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.
Title: Re: LS swap Gurus
Post by: jon316 on March 23, 2020, 02:34:20 PM
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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Title: Re: LS swap Gurus
Post by: jon316 on March 25, 2020, 06:44:56 PM
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 thereís house butt connectors on things and wires cut and tapped. Holy cow!

(https://uploads.tapatalk-cdn.com/20200325/0548654933e093862cd281cc28dbe414.jpg)
This one I have no clue what it is?

(https://uploads.tapatalk-cdn.com/20200325/8a84b3c88ec24edd893ed0e699946cf5.jpg)
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.

(https://uploads.tapatalk-cdn.com/20200325/62121bb4520995bd37ed8b7a6412bda8.jpg)
Since it connects to these three wires, definitely has me baffled.

(https://uploads.tapatalk-cdn.com/20200325/1cdf01c1a10433c2e3ed52f6a4775aea.jpg)
These blue wires tie into the front lights harness? Thatís not stock right it looks to be squeezed on the side of the grommet.

(https://uploads.tapatalk-cdn.com/20200325/19dc45c59ae8ffc7c8a3d0838b03e92a.jpg)
And for the brake switch, which one am I supposed to use? I know on the ecm thereís two one for brake and one that needs power all the time unless brake is pressed to disengage the TC. Iím gonna assume itís the black?


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Title: Re: LS swap Gurus
Post by: bd on March 25, 2020, 09:24:54 PM
(https://uploads.tapatalk-cdn.com/20200325/0548654933e093862cd281cc28dbe414.jpg)

^^^^ factory radio speaker harness


(https://uploads.tapatalk-cdn.com/20200325/8a84b3c88ec24edd893ed0e699946cf5.jpg)

^^^^ 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))


(https://uploads.tapatalk-cdn.com/20200325/19dc45c59ae8ffc7c8a3d0838b03e92a.jpg)

^^^^ 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


(https://uploads.tapatalk-cdn.com/20200325/1cdf01c1a10433c2e3ed52f6a4775aea.jpg)

^^^^ trace it
Title: Re: LS swap Gurus
Post by: jon316 on March 26, 2020, 04:01:40 AM
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 Iím just gonna rip it all out and run new speaker wire and etc.

Thanks for noting the torque converter plug! Didnít 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?

(https://uploads.tapatalk-cdn.com/20200326/9c18221d3b3ce3e098ba96b6703b5bde.jpg)
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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Title: Re: LS swap Gurus
Post by: jon316 on March 26, 2020, 04:33:30 AM
(https://uploads.tapatalk-cdn.com/20200326/a1d189a2e158cb1bcfa62274ee9b2461.jpg)
Another I been trying to figure out is the one for the solenoid. You mentioned it being this one but shouldnít it be smaller one, although their is a lot of wires tapped together there. Iím super confused on what wire starts, what charges the battery, what goes to the post and what shouldnít.

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


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Title: Re: LS swap Gurus
Post by: bd on March 27, 2020, 11:55:56 PM
(https://uploads.tapatalk-cdn.com/20200326/9c18221d3b3ce3e098ba96b6703b5bde.jpg)

^^^^ 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 (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_81_1981_Chevrolet_Light_Duty_Truck_10_to_30_Service_Manual.pdf#page=1080).



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.

Title: Re: LS swap Gurus
Post by: jon316 on March 28, 2020, 03:36:26 AM
Great thank you! Iíll 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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Title: Re: LS swap Gurus
Post by: jon316 on April 03, 2020, 02:24:05 PM
Back again! Now I am having fuel issues. Thankfully most of the gauges are buttoned up and working and I was able to clean most of the wiring up.

I am getting 90psi fuel pressure! Iím thinking for sure itís the fuel filter regulator, as I unhooked the return portion and Iím seeing zero fuel come out. Issue is I installed it right after the tank, and then the inline pump down the feed line under the cab. Could the filter being before the pump cause this? I had come across a few builds that did it this way and no issues. Could it just be a faulty regulator is that common?


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Title: Re: LS swap Gurus
Post by: bd on April 03, 2020, 03:55:21 PM
So, you installed the pressure regulator between the fuel tank and the pump on the pump's inlet side?  How did you expect the regulator to work?  The regulator should be located after the fuel pump and filter.
Title: Re: LS swap Gurus
Post by: jon316 on April 03, 2020, 04:01:21 PM
Shouldnít it not make a difference if itís pushing or pulling itís the same direction. Anyways yea I swapped it and it worked. Weird because Iíve seen other setups that way. Oh well. Tomorrow is another day. Gauges are working and engine is running and idling great. Oil pressure is not working but that could be the sender I received or not making good contact perhaps.


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Title: Re: LS swap Gurus
Post by: bd on April 03, 2020, 04:49:00 PM
It's a "pressure" regulator, not a "suction" regulator.   8)
Title: Re: LS swap Gurus
Post by: jon316 on April 06, 2020, 04:11:41 PM
It's a "pressure" regulator, not a "suction" regulator.   8)
Touchť !


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Title: Re: LS swap Gurus
Post by: jon316 on April 06, 2020, 04:18:36 PM
So got all the gauges squared out thank God. Not trying to figure out the headlights and some wiring coming out of panel. The headlights were rolled up tucked into the firewall by drivers feet.

I stretched the harness out and made my best guesses. The headlights are inverted on drivers the high beam on top etc. filament ok drivers side bulb blown but has an extra wire?! Also found another wire coming from headlight harness with a rubber grommet not sure what for?

(https://uploads.tapatalk-cdn.com/20200406/73973f6d8cafb9f0e7b0aeb7dc3dfc78.jpg)
Look at this nightmare! That light blue wire what the heck is that for? There was a heck a lot if tapping in this truck. One tapping into main feed for wiper motor. Which I removed. But now when I turn headlights on or when I randomly start the truck wipers turn on and donít shut off unless I cycle the wipers on and off.

(https://uploads.tapatalk-cdn.com/20200406/550d8daf3f8b9f9629ef0fe58e2cace3.jpg)
This is that wire I mentioned looping into the headlight harness.

(https://uploads.tapatalk-cdn.com/20200406/28158fc559f279176907f09aa5164c61.jpg)
These wires come out on the lower side of the fuse panel. I canít distinguish what the panel says from the other end. (https://uploads.tapatalk-cdn.com/20200406/2df5c37de18c06975d4cdf20338466dc.jpg)
Same as picture above.

(https://uploads.tapatalk-cdn.com/20200406/53564d4ee4a6daa72e26ff863e2cc346.jpg)
And this one too, it goes from green to a black with a terminal plug on it?! I thought it might of been horn, but thatís in the headlight harness... so confusing!


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Title: Re: LS swap Gurus
Post by: bd on April 07, 2020, 12:39:03 AM
Every question you've asked is answered by the Section 8C wiring diagrams of the factory service manual, linked earlier - wire colors & routing, circuit numbers, bulkhead connector map, etc.
Title: Re: LS swap Gurus
Post by: jon316 on April 08, 2020, 06:50:30 AM
Was it? Couldnít find it up there. Iím using the mobile version of the app though that could be it.

Another curious question for the ls swap guys, are you running the steam ports still? Came across a few posts of people just capping them? I only have the one hose coming out of the front, the rears are plugged from factory. I did see an adaptor that goes on the top radiator hose and it connects to that. Probably go that route but if itís not needed it would look much nicer without it.


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Title: Re: LS swap Gurus
Post by: bd on April 08, 2020, 08:46:39 AM
Here is the link again:  1981 Service Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_81_1981_Chevrolet_Light_Duty_Truck_10_to_30_Service_Manual.pdf#page=1063).  There is a lot of useful information in that manual.
Title: Re: LS swap Gurus
Post by: ehjorten on April 08, 2020, 09:00:11 AM
Run the steam ports, they are there for a reason.  The rear ones are capped from the factory in car applications because the engine is angled down in the rear.  Some people put the vent back into the top of the water pump.  Some people use that JTR (Jags that Run) adapter that goes into the top radiator hose.  Factory is a small port into the top of the radiator.  I had my radiator modified to add the steam port into it.
Title: LS swap Gurus
Post by: jon316 on May 14, 2020, 03:43:56 PM
So far so good. Got all the wiring squared up just have the little stuff to wire up like cruise control. Now question time.

Truck is running nice, idling super smooth. Issue is sometimes it has trouble starting. Thought at first well itís for sure ground. So added ground. That didnít do much. I check the ground from the coils but figured it canít be that if itís running great WHILE itís running. I would fiddle all the cables while it is and itís good. So I got a scanner and ran codes WHILE it was running. It wonít throw any codes. But it has some in pending while itís running. Not sure why it wonít store them maybe itís just a minor issues.

Says mass air and cam sensors. But the cam sensor in the rear top of engine is new, ac Delco new, and the mas air flow is also new.

The only thing Iím guessing is that it could be the crankshaft position sensor. As I know those can cause starting issues. And itís the only sensor basically that isnít new!

It will sit there and crank and crank and crank. Occasionally when I stop cranking itíll throw a backfire here or there but not every time. Any ideas?

(https://uploads.tapatalk-cdn.com/20200514/47fcc572e21e63605f2ad7a921d81b95.jpg)
(https://uploads.tapatalk-cdn.com/20200514/a1f517ca060ad16df7077156453649b6.jpg)
(https://uploads.tapatalk-cdn.com/20200514/2148590243b3c29b35cd75b40b09e3a7.jpg)


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Title: Re: LS swap Gurus
Post by: jon316 on June 19, 2020, 04:20:16 PM
Changed mass air flow and the cam sensor and got better. Finally drove it but have a caliper thatís seizing up so had to park it again.


Iím having some issues with the trans. It keeps leaking out of the weep hole in the shaft. And itís for sure because that tail is sitting way too low. Iím thinking maybe the crossmember is upside down. But then again it doesnít look like it may slide in the other way due to the chassis. Any ideas??

(https://uploads.tapatalk-cdn.com/20200619/2e562aa6fb72c0f804f0e89c807f6c4d.jpg)
(https://uploads.tapatalk-cdn.com/20200619/309b99942d4567dc86dda462017952be.jpg)
(https://uploads.tapatalk-cdn.com/20200619/320d522e51dc0408d96182bef248d961.jpg)


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Title: Re: LS swap Gurus
Post by: bd on June 19, 2020, 05:01:24 PM
You definitely need to check and set up the driveline angles. 

Regarding yoke weep hole seepage, read Leaking Driveshaft Yoke (http://73-87.com/7387garage/drivetrain/yokeleak.htm).
Title: Re: LS swap Gurus
Post by: jon316 on June 19, 2020, 05:04:58 PM
So the seal in the yoke is bad, or o-ring that is? What a weird issue! Ok Iíll get that swapped out then. As for the driveline idk what else to do!


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Title: Re: LS swap Gurus
Post by: JohnnyPopper on June 19, 2020, 06:54:23 PM
Regarding your 'freezing caliper' it's more likely the flexible rubber line.

They deteriorate inside and will cause oil to be trapped, locking up the caliper.
Title: Re: LS swap Gurus
Post by: jon316 on June 19, 2020, 07:00:43 PM
Ok Iíll check them! Thanks! Iíll be doing some nice wilwood and new rotors so Iíll make sure theyíre working properly.


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Title: Re: LS swap Gurus
Post by: jon316 on June 20, 2020, 09:15:55 AM
So I got this D52 Wilwood kit specifically for the c10....and also a set of rotors. First the rotors are too big, not even the bearings fit. So I said screw it need the truck to run already Iíll run the current rotors for now. And now the brake line bolt doesnít match! What a mission. Any help?


Iím about to just put everything back and rebuild that one caliper. Never dealt with so much issues on a truck. But Iíve worked on mostly OBS trucks and NBS trucks.

(https://uploads.tapatalk-cdn.com/20200620/6234e1facc3bc62212b6c0db819b17a8.jpg)

(https://uploads.tapatalk-cdn.com/20200620/93ff20614adc166251743abfae088115.jpg)

(https://uploads.tapatalk-cdn.com/20200620/25746baa9bd9bf4b8f8c08cafc2ccc46.jpg)


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Title: Re: LS swap Gurus
Post by: jon316 on June 20, 2020, 09:30:02 AM
Iím seeing jb1 and jb3 and jb5.... I have j50? Not sure what rotors and calipers I should use!

(https://uploads.tapatalk-cdn.com/20200620/d2bd4e333e14e96cbf7ca746b1fb32a9.jpg)


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Title: Re: LS swap Gurus
Post by: bd on June 20, 2020, 04:45:50 PM
Based on the VIN and J50 vacuum power brake code your truck was constructed with JB3 brakes.

Brake Tech, what do all the numbers mean.. (http://forum.73-87chevytrucks.com/smforum/index.php?topic=28592.0)
Title: Re: LS swap Gurus
Post by: jon316 on June 20, 2020, 05:03:25 PM
Got it, went to oreillys and stuck with the oem stuck. Matched the best to jb1/jb3 so thatís what I went with and worked out. Thanks!!


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