Mark Houlahan
Tech Editor, Mustang Monthly
January 19, 2014
16 Disconnect the main headlight feed from the left front headlight. This can be done in the front of the left wheel well area. We pushed the headlight feed connector back through the core support opening and plugged it into the relay harness, as seen here.
17 The left front headlight pigtail now plugs into the headlight relay harness instead of the factory Ford harness. Finally, the provided extension harness is plugged into the last relay connection and routed across the front of the car using the factory headlight harness retainers and is plugged into the passenger headlight pigtail.
18 The trigger wire from the wiper switch is cut to length and the provided female wire terminal is crimped onto the end of the trigger wire. We added a length of shrink wrap to protect the connection and then connected it to the available male terminal on the relay block.
19 The provided circuit breaker for the battery feed to the relays is installed next to the relays and the battery feed wire’s pre-terminated end is slipped over the circuit breaker stud and secured, as seen here.
20 The battery feed wire is routed to the battery via the same route as the passenger headlight extension. The instructions call for cutting the wire to length and crimping the provided ring terminal onto the end of the wire for connection to the hot side of the starter solenoid. However, this ’68 Mustang had aftermarket battery cables and terminals with an open connection on the terminal, so we simply stripped the wire end and inserted it into the terminal block on the positive battery terminal.
21 The finished installation tucks nicely under the windshield washer reservoir and all wiring is cleanly routed with no cutting of the factory wiring necessary. Now when the owner hits inclement weather and uses his windshield wipers, he not only has the ability to use a timed intermittent function dependent upon road speed and amount of rain, but the Mustang’s headlights will automatically turn on for an added measure of safety.

Muscle Car Switch Parts Used

Part Description Part Number Price
Intermittent Wiper Switch FM6768WI $95.00
Automatic Headlight Controller M678HCIO $45.00
Total: $140.00