Code .7.1 Cruise Control Brake Switch Circuit

Fig. 27 Cruise control brake wiring circuit. 1984:

Fig. 28 Cruise control brake wiring circuit. 1985:

On some early DEFI equipped vehicles, without Cruise Control, Code .7.1 will not pass because a non-Cruise Control brake light switch was installed. To test Code .7.1 on these vehicles either, short the wires at the appropriate connector or replace the brake light switch with a Cruise Control type switch.
The cruise control brake switch circuit sends a 12 volt signal to the ECM except when the brake pedal is depressed. When the brake pedal is depressed, the switch is opened and the brake signal is zero volts. Code .7.1 indicates that the brake switch signal does not drop from 12 to zero volts when the brake pedal is applied. To diagnose the system proceed as follows:
1. Disconnect cruise control brake switch electrical connector, then turn ignition on.
2. Connect test lamp lead to ground and probe switch electrical connector with other lead.
3. If test lamp lights while probing only one side of switch but not the other, replace switch.
4. If test lamp lights when both sides of switch are probed, switch has continuity. Depress brake switch and probe brake switch connector circuit 919 (1985, 86). If lamp lights, brake switch is shorted and must be replaced.
5. If test lamp does not light while probing circuit 919 (1985, 86) with brake pedal depressed, switch is operating satisfactorily. Check for open in circuit 919 (1985, 86) and repair as necessary. If circuit is satisfactory, replace ECM.
6. Check three amp cruise control circuit fuse. If fuse is satisfactory, check circuit 904 (1985, 350) for open and repair as necessary.
7. If fuse is blown, a short circuit to ground in the ECM wiring harness is indicated. Check circuits 904 and 919 (1985, 350, 86, 87, 84 and 397) and repair as necessary.