Originally Posted by s10gmconversion
I have the money I just feel like im cheating if I buy a premade harness. I would rather modify the harness myself and have the satisfaction on knowing I did the whole swap, not hired out the most difficult part of the whole swap. If you have time I would love if you could pm me a basic rundown on modifying these harnesses.
i chose a 2003 tahoe as a donor and the truck is a 2001 so the wiring wasnt to different. The starter took the most thought.. Basically i took all the pinouts and decided where the wiring needed to go.
First thing i would do is strip the wiring down. I removed the rear o2 sensors because they were taken out when i tuned the ECU. The transmission for now is still the 4l60e; sane as the tahoe donor. I also took the tahoe gauges and programmed the ECU to them. I also had all my EVAP and emissions taken out.
Ill start with the easy stuff.. On the s10 you'll have a wire on the drivers side of the tranny called plug c104 that controls your fuel pump and evap.
this plug has a 6 pin plug and 5 wires, youll use them all. I stripped the 4.3 wiring harness to use the plug and about a 1.5' pigtail (cut down later). This will run up by your fuse panel under the hood.
I relocated the s10 c100 wire from the passenger side to the driver side and put it by the fuse block as well.
the ECU is driver side next to the radiator in front of the fender.
Now is the fun part!
I solder all my wires so invest in a soldering gun, heat shrink tubing, and rosin core solder.
I repined the Instrument Gauge Cluster for the silverado gauges. Looking at the s10 gauges and numbers ill list where each moves to. It is up to you to keep track of the wires once they are pulled.. Oh yeah i used a straight dental tool to remove the pins, super easy.
a2 to a1
a3 to a2
a4 to a3
a5 to a4
a6 to a5
a7 to b6
a8 to a10
a9 to a8
a10 to a9
a11 to b2
b2 to a7
b3 to a6
b11 to b10
Now for this to work you need to solder together the oil level wires that usually run to the Vortec oil pan as well as the coolant level wires (forgot wire colors but they are easy to locate). This way the gauges wont message you for low coolant and low oil. If low oil is read then the engine wont run or start.
Now the 5.3 has a c152a plug and its blue with purple tape around the wires if i remember right. These will feed the pigtail from the fuel system ran to the fuse block.
C (gray) goes to the gray wire
B(dk grn) goes to the dk grn wire
F (white) goes to the white wire
J (Black) goes to the black and white stripe wire
E (Purple) goes to the ppl wire
I believe i had 2 wires on this plug that didnt get used and i just cut and heat shrink the ends and taped with the rest of the wires.
On the c100 plug.. I cut the plug c101 plug off of the 4.3 harness leaving me about 8" of wire to work with. So from the 5.3 harness i cut these wires and soldered to the wires in the position on the s10 c101 plug:
A to P
B Not Used
C to G
D to M
E to E
F not used
G to L
H to R
J to C
K to A
L not used
M to H
P not used
R to D
S not used
But dont button up all these wires just yet, youll use some wires from the c2 plug to go to this harness.
Now to the c2 plug.. Im 99% sure everything is correct but i can only tell you mine runs just fine with no issues but cant say 100% that everything is correct.
On your 5.3 plug youll want to mark all the pink wires with the circuit numbers they relate to. Pink wires means there is a switch or component needing power so usually as long at these pink wires have power at the proper time then everything is good to go. from the truck plug youll place the truck pins in these positions; again i sued the straight dental tool to remove pins. These numbers are for all the possible wires so my harness didnt even have all these but ill list everything i could find. Remember on the 5.3 harness the first number moves to the second number..
A1-A8 not used (cut and cap)
A9 to B11
A10-B2 not used
B3 to D4
B4 not used
B5 goes to the c101 plug to the B position wire
B6 to A9
B7-C3 Same/not used
C4 to A9
c5-c9 not used
c10 to d10
c11 to c10
c12 to e10
d1-d7 same or not used
d8 to f9
d9 to f10
D10-E2 Not Used
E3 to b12
e4-e5 not used
E6 to e10
e7 to e10
e8 to b9
e8-e11 Same or not used
F1 not used
F2 Not Used
F3 to c12
F4-F5 Same or Not used
F6 to E7
F8 Not Used
F9 to c8
F10 to E2
F12 Not Used
I had a lot of wires going to a few places.. I soldered a few together but the 10 slot is a 12V rail so the d10s i just spread over this rail in open places.
That was probably my least favorite part of the swap!
So now on to the electric fans.. I just used the two ebay special slim fans and the currently run together. So on your ECU youll want to have the electric fans programmed to turn on at around 180-190 degrees. If youre running AC then youll need to program two fans with 3 relays so use the wiring diagram on this thread.
for one fan or two on the same relay youll take your 12v relay and find a home for it. Take a pin out of your 4.3 ecu harness (i chose black and give yourself about 2' of lead so you can place the relay anywhere you need. Pin the wire to the 42 on the blue connector. Just use our dental tool to poke a hole in the yellow rubber and push the wire through until the pin is in position. Put the ECU back together.
Now head to the fuse block and find the c1 plug (Long block white) and pin A9; the wire should be pink and is hot when the key is on run or start. Solder a red wire to the pink wire and run to the relay location.
On your relay solder the red wire to the 85 pin and the black to 86. soooo as long as the key is on and the ECU reads the trigger temp this will ground out the relay completing the circuit. So lets finish the circuit..
Your fans will have a + and - wire. Run the plus to a constant hot. I chose the bolt from the battery to the fuse block and added a crimp connector and tightened it on. the - wire will run to the 87 pin on the relay. Take another wire from the 30 pin and ground it to the frame or battery. call this relay MAIN
Tape the wires separately or heat shrink so water wont be an issue. Basically once the circuit triggers it will connect the two grounds, turning the fan on. For trucks with AC youll want to run a pin from the ECU red block pin 33 to trigger a relay seporately for the AC but youll run it the exact same way except for the black wire which will be from pin 33 for this relay. (can also be used for high cool and low cool fans)call this relay AC
With AC youll also want to run a 3rd relay that is triggered by the first cooling fan.. Youll do this by running the red wire to 85 (note all red wires will go to all pins 85 on the relays. Your + on both fans should always be hot to the battery via the block or wherever. Your - should have one fan to the MAIN and one to the AC so this 3rd relay will tie it all together so when the temp relay kicks on then both fans will run.Youll take the wire from MAIN pin 86 (black from ECU) and run it to pin 86 to this relay. You will take the 30 pin on this relay and run it to pin 86 as well (or ground). You will then take pin 87 from this relay and run it to pin 86 on the AC relay. This way the fans run off different relays and the third relay controls the second fan without back feed to the ECU. You can accomplish this with 2 relays but i like to prevent backfeed on the temp side because chances are AC fan will run more than hot fan.
As i said this should work for 4.8, 5.3, and 6.0 wiring harnesses. of similar years. My donor and s10 were close enough that this was fairly painless. These shouldn't be much different with the 2.2 vs the 4.3 either and this is for a 2wd setup although the wiring diagrams cover 4wd but youll have to check the pinouts and wiring for the 4wd. This is only how i did it and the ECU was programed to the tahoe with the s10 gear and tire size. basically it thinks its a big truck and this saves me from having to repin the ECU which is no fun at all and would never do it unless i had to. Its also a good idea to have the wiring schematics available for both vehicles in case there are any issues. Marking all the wires that youre unsure of saves time in troubleshooting.