TCC Brake Switch Wiring

[MDPotter]

I've been researching but haven't been able to find a definite answer. I've got a Gen III LS and a 4-prong brake switch and will be installing LED tail lights. On my dad's Gen IV with a 2-prong brake switch, we installed a 470 ohm resistor but we did that so the TCC wire would see 12v. With my 4-prong switch, is that necessary? Below is the wiring diagram from PSI. I will be connecting the red to switched 12v, purple to TCC wire out of the PCM, and white and orange to the brake switch wiring from my American Autowire harness. Do I need to install a resistor inline on the white or orange wire for the tail light wiring?

[ls1nova71]

No resistor needed. Just hook it up the way you described.

[19SIKtySix]

Originally Posted by MDPotter

I've been researching but haven't been able to find a definite answer. I've got a Gen III LS and a 4-prong brake switch and will be installing LED tail lights. On my dad's Gen IV with a 2-prong brake switch, we installed a 470 ohm resistor but we did that so the TCC wire would see 12v. With my 4-prong switch, is that necessary? Below is the wiring diagram from PSI. I will be connecting the red to switched 12v, purple to TCC wire out of the PCM, and white and orange to the brake switch wiring from my American Autowire harness. Do I need to install a resistor inline on the white or orange wire for the tail light wiring?

Attachment 1893751

Originally Posted by ls1nova71

No resistor needed. Just hook it up the way you described.

I'm still a newbie when it comes to wiring, what do they mean by switched 12v?

Is it the same as keyed or ignition? I'm wiring in this same part with LED taillights for my LS swap.

Thanks for asking the question MDPotter.

[MDPotter]

Vehicles run off 12v. It's not really necessary to mention it in posts, but we still do. Switched means that the source is hot with the key in run and crank position and not hot when in accessory of off. With LS harnesses, pink wiring is switched and orange is constant (battery) hot.

[solidaxel]

Keep us posted on your results for the TCC

[19SIKtySix]

Originally Posted by MDPotter

Vehicles run off 12v. It's not really necessary to mention it in posts, but we still do. Switched means that the source is hot with the key in run and crank position and not hot when in accessory of off. With LS harnesses, pink wiring is switched and orange is constant (battery) hot.

OK, that's what I was thinking but I just wanted to make sure. I'm going to be wiring this up soon, just wanted to make sure I understood how the wires went.

Are you by any chance running LED lights?

[MDPotter]

Originally Posted by 19SIKtySix

OK, that's what I was thinking but I just wanted to make sure. I'm going to be wiring this up soon, just wanted to make sure I understood how the wires went.

Are you by any chance running LED lights?

Yes, we installed LED tails on my dad's 64 Gen IV swap and I will be installing LED tails on my 68 Gen III swap.

[19SIKtySix]

Originally Posted by MDPotter

Yes, we installed LED tails on my dad's 64 Gen IV swap and I will be installing LED tails on my 68 Gen III swap.

I'm running Octane Lighting LED taillights and GENSSI LED headlights. My passenger taillight is very dim, even when the turn signal is activated. Octane Lighting told me to connect the brake light switch and see if that helps, if not then they told me to try adding a resistor to the taillight.

I want to see if the problem is fixed by having the brake switch hooked up, but have you experienced any issues like that?

I know the taillight bucket is grounded once installed, but should I run a separate ground to the taillights? The driver side works just fine.

Also I installed LED flashers (with the built in ground) and the blinkers speed is slow and steady, like it should be.

[MDPotter]

I don't see why you couldn't add a resistor for the tails, we had to for them to work along with the LED flasher. The reason for the resistor on the 64 is because the PCM couldn't see the voltage because the draw from the LED tails was so low.

We didn't run a separate ground and it works just fine - nice and bright. It grounds through the socket in the taillight housing and then through the screws into the taillight housing in the bedside. So make sure that socket is clean - take a piece of emery cloth or sandpaper so things are making good contact. Without a good ground, lights on these trucks don't work. It's possible that your issue is just a ground issue, we had the same problem.

[19SIKtySix]

Originally Posted by MDPotter

I don't see why you couldn't add a resistor for the tails, we had to for them to work along with the LED flasher. The reason for the resistor on the 64 is because the PCM couldn't see the voltage because the draw from the LED tails was so low.

We didn't run a separate ground and it works just fine - nice and bright. It grounds through the socket in the taillight housing and then through the screws into the taillight housing in the bedside. So make sure that socket is clean - take a piece of emery cloth or sandpaper so things are making good contact. Without a good ground, lights on these trucks don't work. It's possible that your issue is just a ground issue, we had the same problem.

Yeah the taillights I bought came with new buckets and taillight housing. I'll try the resistor after I get the brake switch hooked up, see if that fixes the problem. I really enjoy the LED lights, looks so much cleaner and def brighter! Thanks for the info MDP, I appreciate it.

[TA_C10]

Potter, are you going to have cruise control? I was told to add resistance to the wire(I used a relay instead of resistor) on the white wire on brake switch because i'm using LED lights plus DBW CC. The cruise needs to see 12 volts to kick off and the LED lights supposedly don't draw enough voltage for the TAC module to see it.

Here is LS1Nova71 post on this: http://67-72chevytrucks.com/vboard/s...d.php?t=511477

[MDPotter]

No cruise control for me. I would follow what ls1nova says, he knows his stuff.