I looked on my CD, there is a wire running down from the amp to... I can't tell, except it's near the crank shaft, just to the drivers side and below of timing tab. However, a friend has a 123 Euro, and he tells me there is sensor on his. He has non-working cruise as well, albeit a servo unit, it's a '79. You'll need a different dash, at least the one gauge, bracket, said amp, plug for amp with wire to sensor, plug for gauge. Most of which you may obtain at a pick'n'pull, if available. I think the only new part you need would be the amp itself as they are prone to failure.

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83 SD

84 CD