More likely it's the wire to the Hall Effect pickup in the speedometer.

Neither wiring diagram is going to help you much, the 87 does NOT have electronic engine control (just idle speed control).

You will need a diagram for the 87 300D.

Faulty cruise control on these cars has three failure points:

1. Amplifier solder joints cracking

2.Actuator draws too much current, causes #1 sometimes, check before replacing amplifier

3. Bad Hall Effect pickup in speedo (causes uncontrolled speed, especially "runaway".

Bad stop lamp will also cause it to fail to run (it grounds via the filaments in the stop lamps, that way there is no voltage when the stop lamps are illuminated).

Peter

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!