DBW Cruise Issue

[jackyl9999]

I installed a cruise control setup today on my 70 gmc and it will not activate.

I used the parts and method in this post by ACKATTACK.

http://67-72chevytrucks.com/vboard/s...d.php?t=398006



I checked all the relays and they are working as shown in the above thread. I double checked my wiring from the TAC module as well. It will not turn on (I can hear the relays though) or respond in any way.


Any ideas for what I need to look for?

[jackyl9999]

Also, I am using a GPS speedo, if this has anything to do with the issue.

[ls1nova71]

Have you verified that you are getting a constant 12v at the 'on/' wire pin 14 on the TAC? Orher than that, make sure you have the brake switch adjusted properly.Also, make sure pin 6 is hooked to the brake light switch that is hot when the brakes are applied. You dont have LED tail lights do you?

[jackyl9999]

Yes I do have Led Tail lights.

[ls1nova71]

Originally Posted by jackyl9999

Yes I do have Led Tail lights.

Try swapping them out for a pair of 1157's and see if it works. The cruise needs to see ground through the brake lights and LED's won't do it so it usually won't work. If that fixes it, you can add an extra 'artificial' load to the circuit to allow you to run the LED's.

[BR3W CITY]

Originally Posted by ls1nova71

Try swapping them out for a pair of 1157's and see if it works. The cruise needs to see ground through the brake lights and LED's won't do it so it usually won't work. If that fixes it, you can add an extra 'artificial' load to the circuit to allow you to run the LED's.

Ya some guys will dangle an 1157 somehwere hidden to create load, but thats a short/fire hazard. You can get little resistor packs that create the same load for a few bucks online, and some folks just make em.

[dayj1]

These guys are probably right about the LED tail lights. I'll add that the GM PCMs are not quite as picky about low resistance and don't have to have the resistor packs.

Stop at your local Radio Shack and pick up a pack of 1K ohm 1/2 watt resistors. There will be 5 of them in the pack, but you just need 1. I find it easiest to place it at the tail light but you can place it near the brake switch if you prefer. It just needs to be connected from the ground wire to the brake signal wire. The resistor is not polarized, so which lead is which doesn't matter. The 1K ohm resistor won't even pull 1/4 watt, so it'll be cool to the touch unlike a spare bulb or resistor pack.

[jackyl9999]

I will give it a shot hopefully this afternoon.

Thanks for the info guys.

[jackyl9999]

I am not going to be able to swap out the 1157 due to my led tail lights being wired in to my harness. (Repop taillight buckets)

I have some resistors left over from my swap. I used them for my tach to cut out some electrical noise.

http://lt1swap.com/lsx_tach.htm

Would they work?


Also does this need to be one side or both tail lights?

[dayj1]

Originally Posted by jackyl9999

I am not going to be able to swap out the 1157 due to my led tail lights being wired in to my harness. (Repop taillight buckets)

I have some resistors left over from my swap. I used them for my tach to cut out some electrical noise.

http://lt1swap.com/lsx_tach.htm

Would they work?


Also does this need to be one side or both tail lights?

Yep, 1K ohm will work fine. I'd feel better about the safety factor with a 1/2 watt, but a 1/4 watt should work as well. You only need a single resistor from the brake signal wire to ground. It won't buy you anything to put one at each tail light.

[jackyl9999]

Got the resistor in today. Put it on and am still not getting any response from my cruise.

I can hear my relays working when I move the switch. So I do not think my issue is there.


Does the cruise need to be turned on in the tune?

[dayj1]

Originally Posted by jackyl9999

Got the resistor in today. Put it on and am still not getting any response from my cruise.

I can hear my relays working when I move the switch. So I do not think my issue is there.


Does the cruise need to be turned on in the tune?

I'm not aware of the ability to enable/disable cruise in the tune. If you're sure that your wiring is correct and that you have the resistor wired in correctly, it could be your VSS. Is the VSS sensor installed in the trans and connected to the PCM? Are your gear ratios, tire sizes, etc correct in the tune?

[BR3W CITY]

I think for all intensive purposes, the engine and computer don't care if the truck is in cruise, at least with GenIII engines. Its possible GENIV is different because of DOD's use in cruise, but other than that...its not like there's "cruise" setting or anything.

[Daaaanz67]

Double check the adjustment on that brake switch, I was stumped with mine and slowly backed the switch away from where it bottoms out and started working. Worth a try.

[aknovaman]

Stop guessing without real data. You guys are funny. You throw suggestions out like popcorn. What's next, replace the gas cap?

OP, go find someone who has HP tuners, datalog what the inputs and outputs are doing and troubleshoot it logically with real data. Otherwise you are just guessing.

In hpt, the satus bits will tell you if the switches are commanding cruise, brake pedal status to the PCM and it will also tell you if the output is enabled among other things.

[aknovaman]

If you really want this thing to work, pm me your phone number and I can talk you through troubleshooting it over the phone with a simple voltmeter.

[jackyl9999]

I am going to drop by and have my tuner take a look at it with HP tuners.

[Hart_Rod]

Originally Posted by jackyl9999

I am going to drop by and have my tuner take a look at it with HP tuners.

Did you ever find a solution to this? Please post. TIA.

[Big Port Jimmy 6]

I've always used a relay with LEDs and cruise.

LED Tail Lights Note

The use of LED tail lights requires a five-function automotive relay to bypass the brake system. LED tail lights do not let the violet wire (cold side of the brake switch) see ground through the brake lights, themselves. Wiring in a relay is as follows:
http://www.rostra.com/manuals/250-4382_Form5260.pdf

[Hart_Rod]

Originally Posted by Big Port Jimmy 6

I've always used a relay with LEDs and cruise.

LED Tail Lights Note

The use of LED tail lights requires a five-function automotive relay to bypass the brake system. LED tail lights do not let the violet wire (cold side of the brake switch) see ground through the brake lights, themselves. Wiring in a relay is as follows:
http://www.rostra.com/manuals/250-4382_Form5260.pdf

I was able to wire a regular bulb into my 3rd brake light to verify that the LED tail lights were causing the problem, the CC works perfect now. I'm going to try one of the LED flashers and see it that will work before I wire in another relay, I already have a enough relays as it is under the dash......

[ls1nova71]

LED flasher wont help.

[Hart_Rod]

Originally Posted by ls1nova71

LED flasher wont help.

Wouldn't this one work? http://www.ebay.com/itm/400740074640...AIT&rmvSB=true

If not, what size of resistor should I wire inline with the LEDs then?

[Big Port Jimmy 6]

Originally Posted by Hart_Rod

Wouldn't this one work? http://www.ebay.com/itm/400740074640...AIT&rmvSB=true

If not, what size of resistor should I wire inline with the LEDs then?

The flasher has nothing to do with your problem, it is the lack of ground through the tail lights that is the issue. If your lights don't flash then do the flasher, the resistor is a work around for the proper flasher, if the cruise doesn't work do the relay. It takes the LEDs out of the circuit entirely. This fix has worked for me on multiple cars for nearly 20 years. Jay

http://www.the12volt.com/installbay/...asp?tid=130800

[Hart_Rod]

Originally Posted by Big Port Jimmy 6

The flasher has nothing to do with your problem, it is the lack of ground through the tail lights that is the issue. If your lights don't flash then do the flasher, the resistor is a work around for the proper flasher, if the cruise doesn't work do the relay. It takes the LEDs out of the circuit entirely. This fix has worked for me on multiple cars for nearly 20 years. Jay

http://www.the12volt.com/installbay/...asp?tid=130800

Gotcha. I'll either wire in a 1/4 WATT resistor as dayj1 suggested or add another relay per your wiring diagram. Thanks Jay!

[ls1nova71]

You don't need to wire up the relay to act as a relay. You can use just the coil side of it wired to the cold side of the brake light switch and ground, the cruise will see it's ground through the coil and allow it to work. This is how I do mine and they work perfectly. I use micro relays, solder the wires to the terminals and tape it up in the harness. You can see a pic in my build thread post #122
http://ls1tech.com/forums/conversion...-c-10-a-7.html It's doing the same thing as a resistor, but they don't get as hot as a resistor can get.