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Cruise control activation with LED brake/tail lights
I have been doing LSX conversions in old trucks for several years now, but just came up against something new. I put a DBW LQ4 in a 1966 Chevy C10 with LED brake/tail lights. They are the ones that have the circuit board built into them and not just a replacement led bulb that I can throw a load resistor in the ground. I of course had to upgrade to the led flashers to get them to blink, but my TAC module is not sensing a load through the lights ground to the brake switch and allowing the cruise to activate. I know there has to be an easy solution to this? My first thought is a resistor in this wire from the brake switch to the TAC, but I believe the PCM will throw a code for to low or high of voltage through this feed. I need someone to help me think this through, Thanks guys!
You can use a resistor, but they build a lot of heat. What I usually do is take a micro relay, and wire it from the cold side of the brake light switch to ground, on the 85 and 86 terminals. The coil part of the relay will have enough resistance to make the cruise work. If the clicking when you hit the brakes bothers you, you can take it apart and remove that part of the relay. Post 122 has a pic of what I did. https://ls1tech.com/forums/conversio...-c-10-a-7.html
LS1nova71, I greatly appreciate it! Thank you so much. I will get one and try this. My brake switch is a bitch to get to. Can I just tap into the wire from it going to the TAC module you think or do I need to go right to the switch prong? It's pretty thin gauged wire I guess. May not take it huh?
The stuff LS nova71 KNOWS and does amazes me. A lot !!!!!
Thanks for sharing your knoledge.
You guys are going to give me a big head!
Originally Posted by AaronOregon
LS1nova71, I greatly appreciate it! Thank you so much. I will get one and try this. My brake switch is a bitch to get to. Can I just tap into the wire from it going to the TAC module you think or do I need to go right to the switch prong? It's pretty thin gauged wire I guess. May not take it huh?
You can tap into the wire going to the TAC pin #6. It will be the wire that is hot with the brakes applied, it doesn't care where it is.
Went to get a micro relay today. They wanted $27. It was a 30 amp and this brought up a good question. Does it matter if it's a 10,20,30 amp? Thought that was kinda spendy for one.
Damn, that's robbery! I usually get them at the pick n pull for a little bit of nothing. If you want to pay shipping I can send you a few. Not sure where you're located, but guessing Oregon..... shouldn't be more than 5 bucks I would think. Also, I believe they are 20 amp relays, but to be honest I am not positive on that.
You can use a resistor, but they build a lot of heat. What I usually do is take a micro relay, and wire it from the cold side of the brake light switch to ground, on the 85 and 86 terminals. The coil part of the relay will have enough resistance to make the cruise work. If the clicking when you hit the brakes bothers you, you can take it apart and remove that part of the relay. Post 122 has a pic of what I did. https://ls1tech.com/forums/conversio...-c-10-a-7.html
Great info as always Eric. I have a question for you about the heat built up by the resistor. Since you usually only have your foot on the brake for a short period of time, are you really building up much heat? Maybe I'm missing something. Thanks - Rob
I certainly appreciate that offer. I found one for $16 which will be worth it for cruise and the instant gratification without waiting on the USPS snail mail. They shut our pick-n-pull down last year cause of theft. Sucks! They said to many people were throwing stuff over the fence and going back for it that night. Too bad people like that ruin it for everyone...... I was there every week for something.
Great info as always Eric. I have a question for you about the heat built up by the resistor. Since you usually only have your foot on the brake for a short period of time, are you really building up much heat? Maybe I'm missing something. Thanks - Rob
Ok, so I bought the relay and tried it. I have the wire to the TAC module on the cold side of the brake switch (yellow in my case) going through #85 and #86 on it is grounded. I get 80 ohms through the relay until the brake pedal is pushed. I still can't get cruise to work. Is it to much load now? I ohm'd an 1157 bulb and only got 1.1 through it. What am I doing wrong here?
It's not going to be too much of a load.. Couple of questions and I'm sure we can get you going. First, what cruise switch are you using? Also, does the relay click when you pres on the brakes? Get back to me on those, and if they pan out, I can give you some trouble shooting tips to go through to figure out what's going on.
Great info as always Eric. I have a question for you about the heat built up by the resistor. Since you usually only have your foot on the brake for a short period of time, are you really building up much heat? Maybe I'm missing something. Thanks - Rob
I tried a resistor way back when I couldn't get the turn signals to flash, and at least the one I used got hoter than I liked pretty quick, so I just swapped to the relays and never really looked back. Lol! Maybe there are some that dont get as hot, but I never looked beyond the ones I tried.
It's the 4-wire style out of like an early GM van. I tested the switch before the column was installed and then also after it was wired in. I am getting power through it and the momentary switches are all giving power up to the TAC. That is what has me baffled. It's testing like it should. After going through all that is when I started digging and found the TAC needing to sense a negative load with the LED lights and started this thread. Totally baffled at this point.
Not sure why this picture shows three contacts on the plug? Mine has 2 on each side, but same switch.
If that's the switch you have and it is a 4 wire, then it's out of an 83-4 chevy truck, vans only used that switch in '81. But that's beside the point. Try adjusting the brake switch in a little bit and give it a try. The two opposing sets of contacts in the brake switch are not always even, sometimes even though the brake lights are not on meaning that set of contacts is open, the other set may not be completely closed. Also, do you have both brake switch wires hooked up? The one to the TAC and the one to the PCM, they're opposite, PCM needs power with brakes not applied and TAC needs power with brakes applied.
I already have the switch set so it takes a bit of throw to get it switched. Yes, the brake lights and TAC wire are on the NO side and TCC is on the NC side. As far as the relay clicking, I opened it and removed the arm like you did.
I got it! I'm an official dumbass.....The night before I installed the relay yesterday I had pulled power to the cruise from the fuse box. Well........................ I forgot to plug it back in after getting the relay in and test driving yesterday. I crawled back under there today to check the fuse and retest everything and realized I had forgotten to plug power back in. It now works as advertised. Thank you so much for all your help. Love guys like you on forums I hit. Worth your weight in gold to people like me. I owe you a beer.......
Cool! Glad you got it going! I figured it was going to be something small, it's usually the small things that get you when you're looking for something big.....
04-08-2017, 12:04 AM
Cruise control activation with LED brake/tail lights 
