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I have an L76 motor and 6L80 trans, all out of a Pontiac G8. I bought a PSI wiring harness. They had to make one because they were not doing a standard 6L80 harness back then (2 yrs ago) when I put it in. So I'm all done and ready to drive but I noticed my brake lights staying on. I checked the two purple wires for the Converter lock up and 1 wire has 7 volts on it and the other has 9 volts on it. I called and talked to PSI and we checked and made sure the wires were right and a few other things, but can't figure out what is wrong.
The only solution they have is for me to pull the harness out and send it back. Before I do this, does anyone have any ideas of what may cause this. Could it be caused by the tcm or pcm tune or anything else?
Any help would be greatly appreciated - If I pull this harness out it is going to set me back a month.
What brake light switch do you have? Something from the original vehicle or a newer one that goes with the swap? Do the lights go off when you unplug the brake light switch?
Almost positive it's not something in the computer or tune. Your brake lights operate on their own, and are not connected to the computer at all except through the TCC (the computer has to know whether your brakes are being applied or not through the brake switch). But again, your brake LIGHTS are not getting info through your ECM or TCM.
Before I pulled the harness out, I would buy a new brake switch. PSI has one for like $20 I think.
Thanks for the replies. I do have the psi brake switch. I have the two purple wires (converter lock up wires) loose and seperated and I am getting 7.2 volt from one wire and 9.2 volts from the other wire. This voltage was back feeding through the brake switch keeping the lights on. Im trying to figure out why Im getting voltage on these two wires. One wire is from the tcm and the other from the black connector on the pcm.
Yes the brake light go off when I remove the converter lock up wires
Last edited by Blazincopper; 06-17-2015 at 12:57 PM.
hmm, now that I read your post carefully, you say you have 2 purple wires. I only had one purple wire. Trace it back to the computer and make sure you're running the right wire to the switch.
I spent a couple hours on the phone with PSi and we checked the pin location and they seem correct. The issue is that I have approx 8 volts on the purple wires all the time when the key is on. I am suppose to be sending 12 volts through these wires to the converter lock up when I press the brakes. From what PSI says, there shouldn't be any voltage on the wires unless they are hoooked up to the brake switch and I press the brake.
I spent a couple hours on the phone with PSi and we checked the pin location and they seem correct. The issue is that I have approx 8 volts on the purple wires all the time when the key is on. I am suppose to be sending 12 volts through these wires to the converter lock up when I press the brakes. From what PSI says, there shouldn't be any voltage on the wires unless they are hoooked up to the brake switch and I press the brake.
DID YOU EVER FINGER THIS OUT? I'm having the same exact issue where my TCC wire has 9 volts when it shouldn't. thanks for any input you have on this issue.
The OP hasn't been on here in 5 years, so he's probably not going to answer you... That said, it sounds like you have the TCC wire hooked to the wrong terminal of the brake switch.
The OP hasn't been on here in 5 years, so he's probably not going to answer you... That said, it sounds like you have the TCC wire hooked to the wrong terminal of the brake switch.
i have it connected properly. I’m just getting voltage at the TCC wire when there shouldn’t be any until the brake is applied. Just really wierd?
i have it connected properly. I’m just getting voltage at the TCC wire when there shouldn’t be any until the brake is applied. Just really wierd?
So are you saying you're getting voltage on the TCC wire when it's plugged into the brake switch and the brakes are not applied? If so, that's correct. When the brake is applied power is sent to the brake lights and shut off on the TCC wire to unlock the torque converter. What brake switch are you using?
i have it connected properly. I’m just getting voltage at the TCC wire when there shouldn’t be any until the brake is applied. Just really wierd?
You have not really given any pertinent information about what exactly you are working on, but I am assuming you have a GenIV engine since those are the ones that the TCC needs power only when the brakes are applied rather than the GenIII that needs power when the brakes are not applied. If that's the case, and you have the wire hooked up to the switch correctly, and you are still getting power on that wire with the brakes not applied, then either you don't have the switch adjusted right, or maybe the switch is bad. Are your brake lights on? If that wire is hooked up to the brake light side and the brake lights are not on, then there is no way you could have power on that wire, which is why I said it may not be hooked up correctly.
You have not really given any pertinent information about what exactly you are working on, but I am assuming you have a GenIV engine since those are the ones that the TCC needs power only when the brakes are applied rather than the GenIII that needs power when the brakes are not applied. If that's the case, and you have the wire hooked up to the switch correctly, and you are still getting power on that wire with the brakes not applied, then either you don't have the switch adjusted right, or maybe the switch is bad. Are your brake lights on? If that wire is hooked up to the brake light side and the brake lights are not on, then there is no way you could have power on that wire, which is why I said it may not be hooked up correctly.
gen iv is correct. Single wire to TCC
i have replaced the switch but the issue is there is power to the tcc wire BEFORE i even plug it into the brake signal switch. There is only two ways to hook up the tcc wire to the switch (2 prongs towards the back) and I’ve tried both. Which still brings me back to the fact that the tcc wire has 9v to 10.8 volts (when engine is running) BEFORE its even on the brake switch.
I just talked to Speartech about this the other day. On my Gen 4 LC9 if I recall I just hooked it to the cold side of my brake switch and it seems fine for the most part for about 8 years now. Occasionally I've had it lunge when stopping but I think that is something else. For my Gen 5 L83 I was looking at their wiring diagram and it wasn't making sense to me. I thought I needed it to see 12v+ when the brakes were applied but if you follow their diagram it just gets a ground. The tech support guy (if I understood correctly) told me it is sending out a signal that needs to see a ground for the TCC to release. This diagram is for LED lights but it should work to complete the circuit don't you think?
edit:actually now that I look at it again I think I'm still confused because it will be floating when powered.....ground when no brake applied....now I'm wondering again lol.
I’m having the same issue with my swap. Mine is a 5.3 Gen VI 4L65e. E 38 ECM with a T42 TCM. Engine & transmission, OS systems are all matching from the same donor vehicle. 08GMC 4x4 pickup. I’m experiencing the same thing TCC seems to be locked. I’m getting 9.3 to 9.5 volts on the TCC wire coming from the ECM pin 9 with key on and 10.3 with engine running. I’ve tried going straight to the break switch white wire trying to utilize the bulb filaments as resistance to pull it down the 9.5volts to ground as some have suggested. I’ve tried 1k 1/4 resistor also to pull it to ground also with no luck. Has anyone been successful with this? Help!
ScottR65
This is my first post or comment here, I only joined to ask you if you ever figured this out? I have been pulling my hair out with this for weeks and have the EXACT same issue as you have described and have troubleshooted up to the same point as well. Any luck??
06-17-2015, 11:04 AM
6L80 Trans lock up wiring issue - need help 
