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Need a little wiring help.

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Old 04-25-2010, 08:55 PM
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Default Need a little wiring help.

Donor Rig:
03 Tahoe
5.3L & 4L60E
Harness
PCM

After reading the following on LT1Swap.com and not finding a purple wire in the Blue connector (J1, pin 33 is empty)....I'm totally confused. What am I missing? Could this wire be on a different pin?

FWIW, this is the PCM Data tag info.
Serv.No. 12576106 YCTJ
*86YCTJ922351PY6A* 12579403
HDW No. 12570558

Anyone else run into this problem? Where did you find the TCC wire?

Brake Switch Signal - For automatics with lock up converter, the PCM needs signal when brake pedal is pressed. However, the signal needed is opposite how you're brake lights work. The PCM wants 12v+ constant on this wire when brake IS NOT pressed, and OPEN Circuit when the brake IS pressed. If you vehicle was equipped with a lockup trans to begin with, you probably already have the proper normally closed switch mounted by your brake light switch. If you do not, you can use a relay to perform the same thing. On most relays, there are 5 terminals, 2 of them turn the relay ON when provided ground/power. There are then a normally open leg and a normally closed leg on the relay and a supply. By feeding 12v+ on the supply leg, and hooking the Brake Switch Signal wire to the normally closed leg, you will now have the correct signal for the PCM. When the brake is pressed, 12v+ flows to brake lights, tap into this wire, and run it to the relay to turn the relay on. This will cause the normally closed leg to become open, thus turning OFF the 12v+ signal to the PCM. When you release the brake pedal, the relay will turn OFF, and then feed 12v+ to the PCM.
Old 04-26-2010, 11:22 AM
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The purple wire at C1-33 goes to the brake switch on the brake pedal, never seen a harness without it. Does it look like it may have been pulled out, is there a small hole in the rubber part inside the connector? If so you could just add another wire. The only way I would think it would have never had one is if the harness were from a manual trans truck, but I've never looked at one to say for sure, and since you said it was an auto, it should have it. If it were mine, I'd just add it.
Old 04-26-2010, 01:48 PM
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It's just not there.




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