ECM wires

[Ramiro0727]

Hello,

My son has a 69 Chevy C10 that he is installing a Gen.3 5.3L. The person that was working on his truck wasn't able to finish it. So we towed it home. The truck fires up and all. But we noticed there are extra wires coming off the ECM that are connected to anything? Or we need to connect them. Or we don't need to do anything with this wires. Also we noticed that he had a purple wire coming off the ECM hooked to a brake switch. We have another brake switch hooked up already to the steering column. Not sure why he did this. Can someone help us out.

Thanks,
Ramiro

[ls1nova71]

Those are most likely wires for things like speedo, tach and check engine light. Hard to say exactly without knowing what pins they're on on the PCM connectors. The brake switch wire is for the lock up torque converter so it unlocks when the brake is applied, you would need to put an ignition controlled 12v on the other side of it.

[Ramiro0727]

Originally Posted by ls1nova71

Those are most likely wires for things like speedo, tach and check engine light. Hard to say exactly without knowing what pins they're on on the PCM connectors. The brake switch wire is for the lock up torque converter so it unlocks when the brake is applied, you would need to put an ignition controlled 12v on the other side of it.

ls1nova,

My son is running a Dakota Digital gauge cluster. I will take a picture of where the wires go to when i get home. So where will I mount the brake switch to? So I need to connect 12V ignition controlled to the switch?

Ramiro

[TrybalRage]

Originally Posted by Ramiro0727

ls1nova,

My son is running a Dakota Digital gauge cluster. I will take a picture of where the wires go to when i get home. So where will I mount the brake switch to? So I need to connect 12V ignition controlled to the switch?

Ramiro

The Dakota cluster *can* be wired to the pcm's individual lines, but they also offer an OBD port option. Could be the previous owner used that method, so wires related to that wouldn't do anything.

If you go to LT1swap.com there are numerous pinout explanations that may help you find what those particular wires do.

The purple wire (TCC lockup) is used if you actually have a lockup converter... what trans is behind that motor? It's supposed to receive 12v hot all the time until the brake is pressed. That tells the PCM to release the lockup. So it needs to be somewhere that the brake pedal/arm can hit the button on the end of it.

[Ramiro0727]

Originally Posted by TrybalRage

The Dakota cluster *can* be wired to the pcm's individual lines, but they also offer an OBD port option. Could be the previous owner used that method, so wires related to that wouldn't do anything.

If you go to LT1swap.com there are numerous pinout explanations that may help you find what those particular wires do.

The purple wire (TCC lockup) is used if you actually have a lockup converter... what trans is behind that motor? It's supposed to receive 12v hot all the time until the brake is pressed. That tells the PCM to release the lockup. So it needs to be somewhere that the brake pedal/arm can hit the button on the end of it.

TrybalRage

Yes we purchased another module that goes with the Dakota Digital cluster its the OBD-II interface. So we need to mount the brake switch somewhere where on the brake pedal for it to work correctly? Do we need to remove the brake switch we have on there already?

Thanks,
Ramiro

[TrybalRage]

Originally Posted by Ramiro0727

TrybalRage

Yes we purchased another module that goes with the Dakota Digital cluster its the OBD-II interface. So we need to mount the brake switch somewhere where on the brake pedal for it to work correctly? Do we need to remove the brake switch we have on there already?

Thanks,
Ramiro

I think it depends.

My 85 had a lockup converter on it already, so I'm already set with the wiring.

Your switch may only be to control the brake lights (so you need to keep it) but it unfortunately does the opposite of what you need. It's off until the brakes are pressed, then hot. You need hot, that turns off when the brakes are pressed.

So if true, you have a couple options. I believe the switch you have there might be able to handle both. You could also wire in a relay to provide the signal you need. Or you could run two switches.

If you google search "wire relay brake switch ls swap" you should be able to find some videos.

[Ramiro0727]

Originally Posted by TrybalRage

I think it depends.

My 85 had a lockup converter on it already, so I'm already set with the wiring.

Your switch may only be to control the brake lights (so you need to keep it) but it unfortunately does the opposite of what you need. It's off until the brakes are pressed, then hot. You need hot, that turns off when the brakes are pressed.

So if true, you have a couple options. I believe the switch you have there might be able to handle both. You could also wire in a relay to provide the signal you need. Or you could run two switches.

If you google search "wire relay brake switch ls swap" you should be able to find some videos.

TryblRage,

Well defiantly will Goggle that. Totally lost on trying to finish up my sons truck for him.

Ramiro

[LS short box]

I hate to be the negative Nelly kind of guy but if you want a trouble free start up you may want to consider scrapping the current harness and going with a new harness from one the LS specialists. Nothing can be more frustrating than trying to figure out what that previous builder did or didn't do. Also have your selected harness supplier review the tune in the computer. Just .02.

[AussieinNC]

Did the previous builder provide a summary sheet for the computer tune showing what is set and deleted etc....

If not, it would pay dividends to get a tuner to provide you a dump of the computer settings and pin outs etc....

Just my 2 cents worth...good luck...

[Ramiro0727]

Originally Posted by AussieinNC

Did the previous builder provide a summary sheet for the computer tune showing what is set and deleted etc....

If not, it would pay dividends to get a tuner to provide you a dump of the computer settings and pin outs etc....

Just my 2 cents worth...good luck...

AussieinNC,

According to my son anything that had to do with emissions was deleted on the tune on the computer.

Ramiro

[Ramiro0727]

Originally Posted by LS short box

I hate to be the negative Nelly kind of guy but if you want a trouble free start up you may want to consider scrapping the current harness and going with a new harness from one the LS specialists. Nothing can be more frustrating than trying to figure out what that previous builder did or didn't do. Also have your selected harness supplier review the tune in the computer. Just .02.

LS short box,

Its a 99-06 vortec harness LS1 intake HAR-1090 on what he said.

Ramiro

[ls1nova71]

You need to replace the original 1969 brake switch with that new one. The set of contacts closest to the plunger is where you will plug in your original brake light wires.

I wouldn't scrap the harness you have now if the truck is running unless you just like spending money. Looks like you just have a few wires left to hook up.

[gmc684x4]

Go back your tuner like previous stated have
Ask them for print out and pin out

Its done to the point it runs why blow anouther 700 plus dollars to get anouther harness

Call up Brendan see if he can pull ip the info for you if the tune shop used cant help

http://www.lt1swap.com
brendan@lt1swap.com

[LS short box]

I'm not a tuner or harness supplier just a hot rodder with over a dozen LS swaps under my belt. I just know you could chase both harness issues and tune problems that will drive you nuts. Does the current harness have the relays for the fuel pump and fans? VSS connectors (auto trans plug if you are running an auto) and all engine connectors? If not I stand by previous post and recommend a new harness and a check of your current tune in your ecm. Again just my .02. Do what is comfortable for you.

[Ramiro0727]

Originally Posted by LS short box

I'm not a tuner or harness supplier just a hot rodder with over a dozen LS swaps under my belt. I just know you could chase both harness issues and tune problems that will drive you nuts. Does the current harness have the relays for the fuel pump and fans? VSS connectors (auto trans plug if you are running an auto) and all engine connectors? If not I stand by previous post and recommend a new harness and a check of your current tune in your ecm. Again just my .02. Do what is comfortable for you.

LS short box Yes it does, My son bought a PSI harness (HAR-1090 part number) that's all dummied down needed for a swap. The tuning issue is resolved my son bought one of those cheap ass throttle bodies and we swapped it out to his original one and now it idles fine. My son's friend was wiring the truck for us cause we're new to the whole LS thing but those were some of the things he left cause he didn't have time.

[LS short box]

PSI has a good rep. I was under the impression your friend had reworked a stock harness. Yes per the guys on LS1tech.com the "cheap" aftermarket TB can cause all kinds of issues.
Good luck with your swap.

[Ramiro0727]

Originally Posted by LS short box

PSI has a good rep. I was under the impression your friend had reworked a stock harness. Yes per the guys on LS1tech.com the "cheap" aftermarket TB can cause all kinds of issues.
Good luck with your swap.

Thank you LS short box, My son spoke to the person that was doing his swap. He informed him that we don't need to connect any other of those wires coming off the ECM. The only other concern is connecting the Neutral Safety switch on the steering column. Do I connect it normally like it should be connected?

Thanks,
Ramiro

[aknovaman]

Go here to see pinout/schematics of all LSx engines.

http://www.chevythunder.com/since_it...on_in_1985.htm

You can trace the wires in question back to the PCM and use these schematics to determine their function and how to connect them.

[ls1nova71]

Originally Posted by Ramiro0727

Thank you LS short box, My son spoke to the person that was doing his swap. He informed him that we don't need to connect any other of those wires coming off the ECM. The only other concern is connecting the Neutral Safety switch on the steering column. Do I connect it normally like it should be connected?

Thanks,
Ramiro

Yes, just hook the starter up to the original heavy purple wire and you will be fine.

[bigmoe]

Those wires that you don't need you should cover the ends each with shrink tube and fold them up out of the way. You don't want them touching something or each other and also you may need one some day. Also if it's a PSI harness it should have come with some instructions and labelled wires I would think.