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MG MGA - Cruse Control with LED Tail Lights

Hi ffolks,
I have seen the past discussions about how to rewire connections when LED tail lights are installed in cars with the Audiovox CCS-100 cruise control (CC). My unit still does not engage though I have made the adjustments (install a 5-point relay) and done the diagnostic tests (including new vac tubing).

I have actually seen different ways to make the wire connections to the relay. Has anyone out there actually installed the relay and solved their CC problem? How did you make the green/purple wire (cold side) connection from the brake light switch to the relay (85)(or 86, does it matter, as long as the other is grounded?) and still connect to the tail lights (actually, the flasher/control box)? The car is negative grounded, the brake light switch is good, the tail lights function okay, the CC control panel lights up.

I am about ready to remove the unit for a closer inspection, but am trying to avoid it (it's ensconced under the scuttle). I am beginning to suspect a torn bladder inside the vacuum module, but I suspect that I am missing something else.

Thanks for any help.
Tyler
C.T. Irwin

The brake input to the cruise depends on a high resistance path to ground through the normal incandescent (un-lit) bulb filament. Without this path the input, in computer terms, floats to 12 volts and makes the cruise module think the brake is applied. An led bulb does not supply this path.

The easiest way to determine if the brake input is the problem (as opposed to a malfunction in the cruise system itself) is to temporarily wire an incandescent bulb from the brake switch cold side to ground. The bulb should light when the brake is pressed (brake switch is good). If this solves the cruise problem, the relay wiring is incorrect. If not, look elsewhere.

I cant help you with the relay wiring, I cant see the wire colors. Just follow the diagrams available. The goal is to have the brake signal tied to ground when the pedal is not depressed and tied to 12V when the brake is applied.

That said, there is really no need for the relay at all. You can simply leave an incandescent light hidden somewhere or add a 470 1000 ohm resistor between the brake switch output and ground. Either will supply the required high resistance path to ground.
Bruns

This thread was discussed between 15/04/2021 and 16/04/2021

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