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I have a truck that has a different engine swapped into it. I'm trying to get the cruise control to work and I've tracked the issue down to the Set/Coast switch. The PCM is expecting a 12 V signal when the Set/Coast button is pushed. Right now when the cruise is on there is a constant 12 V going from the switch to the PCM, and when I push the switch it drops to 0 V. I tried using a relay by hooking the switch to 85, 12 V to 30 and 86 and the load to 87. That didn't work.

Talking the stalk apart doesn't appear to be an option. Rather, I should say talking the stalk apart is an option but getting it back together isn't.

Here is what I followed: https://www.the12volt.com/relays/converting-polarity.asp

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  • \$\begingroup\$ Diagrams would help here. Why was the set/coast switch changed? Surely it was the engine that was changed? \$\endgroup\$
    – Solar Mike
    Commented Nov 7, 2021 at 6:29
  • \$\begingroup\$ A modification carried out in an automobile without proper understanding could endanger oneself and others on the road. Hence voting to close. \$\endgroup\$
    – vu2nan
    Commented Nov 7, 2021 at 11:38
  • \$\begingroup\$ Once you insure and prove your NC to NO conversion works to SET the cruise control, how will you make sure the cruise control cancels properly with the brake pedal or the CANCEL button? I think the only way is an actual road test at 40mph or more! \$\endgroup\$
    – GT Electronics
    Commented Nov 7, 2021 at 12:48
  • \$\begingroup\$ @SolarMike - The cruise control stalk was not changed, the engine and PCM were. \$\endgroup\$
    – Nick
    Commented Nov 7, 2021 at 14:34
  • \$\begingroup\$ @vu2nan - This is a Duramax swap, it has been done on thousands of vehicles with plenty of documentation. I understand exactly what needs to be done. I have documentation from Bosch, which is the company that makes the PCM. There is no risk here. \$\endgroup\$
    – Nick
    Commented Nov 7, 2021 at 14:40

1 Answer 1

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The link you followed is to convert polarity, to convert NO to NC see: https://www.the12volt.com/relays/spdt-and-spst-automotive-relays.asp

Connections of coil: switch to 86, 85 to ground; NC contact: +12 V to 30 and output to PCM is 87a.

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    \$\begingroup\$ This worked, thanks! \$\endgroup\$
    – Nick
    Commented Nov 7, 2021 at 21:57

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