harness rewire help
 

ok so im following LT1 swaps you tube videos and I have the exact same harness (2003 Yukon XL dbw)
ive looked and looked but theres a couple questions still.
first; #33 on the blue plug. the purple TCC wire. where does hook up to?
and B; he shows 3 orange wires hooked up to the battery. 20 and 57 on the blue plug but he also shows a third orange wire I think he has it labeled "OBD2".
Where is this wire? which pin is it?
hopefully you guys can help me out. I wrote Jacob but im sure he`s swamped with e mails all day every day

Re: harness rewire help
 

The TCC wire gets connected to the brake switch. My original brake switch in my 66 had 2 prongs, but I purchased a PSI brake switch which has 4 prongs.

Somebody may be able to chime in about using an original still though.

Re: harness rewire help
 

see I thought so but it wasn't mentioned on the videos. its to disengage the cruise right? or is it for the trans system?

Re: harness rewire help
 

I'm pretty sure it has something to do with the trans

Re: harness rewire help
 

I think you cannot used a standard brake switch this may be the wire that controls the tranny and works the opposite way a standard brake switch works. Be sure to research before you finish wiring

Re: harness rewire help
 

Yes, you will need a 4 prong brake switch to make it easy, there are ways around it, but that brake switch is the easiest way. Your original orange and white wires for the brake lights will hook to one set of contacts and the other set will get hooked to the purple wire on one side and an ignition powered 12v on the other. This is the switch. https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds

There will also be a light blue wire that will get hooked to the brake light side of the switch that comes from the TAC module if you plan on running cruise control.

The orange wires are constant hot power wires and hook to the 2 wires on the PCM connectors, the third wire he mentioned goes to the OBD2 connector under the dash, the connector you would plug a scan tool into.

Re: harness rewire help
 

If you are driving a newer truck with the brake light switch under the dash on the column ACDelco D862C is what you need. Use the normally closed contacts for your brake lights/cruise control and the normally open for thhe TCC wire.

jYou can also just leave the TCC wire unhooked. The transmission will work fine, the torque converter just wont unlock as soon as you tap the brakes, instead waiting until your speed drops below the threshold.

Re: harness rewire help
 

I did not use the videos when I did my harness. Rather, I used his instruction on his website.
http://www.lt1swap.com/2004vortec_pcm.htm
Here is a link as it is hard to find on the website. The instruction were/are invaluable both for rewiring and also future diagnostics. I printed it off in color and made hand written notes along the way. Now it is MY new service manual suppliment. I refer back to it often.

Re: harness rewire help
 

The blue TCC wire needs to be hooked up to the brake switch. A 2003 is a gen 3 engine which needs constant 12v (when not on the brakes) and no power when the brake is pressed (achieved through the switch). I bought the switch from PSI, but you'll see above that there are other options. It has to be the 4-blade switch, not the 2-blade. You can use the 2-blade switch, but you have to use a relay and do extra wiring and it gets complicated so I would recommend going with the 4-blade switch that can do what you need on its own: https://www.psiconversion.com/produc.../KIT-1002.html

I used the same blue/green sheets for my 04, but I'm not seeing a third orange on the blue plug. But you do need an orange to the OBD2 port in the cab - it needs constant 12v. If I recall correctly, I added this wire. It comes from your standalone fuse block and runs into the cab.

I had Brendan reprogram my PCM, but I've never been able to get an email back from him either.

Re: harness rewire help
 

The third orange wire doesnt come from either connector, it is just tied in to the battery hot for the obd II port.

Re: harness rewire help
 

ok guys great thank you!!!
now I know that that obd + wire is a constant power source, not an ignition switch. thank you. as for the purple TCC wire, that goes to a 4 pronged brake switch just like a 700r4 needs then correct? ill look up the info you guys provided me now. thank you guys so much!

Re: harness rewire help
 

The TCC wire needs a ignition hot source when brakes are NOT applied, you can do this with the brake switch or you can also do this through a relay. And you are welcome.