How to Replace the Ignition Switch on a 1978 Chevy Truckby Jack HathcoatUpdated November 07, 2017
Items you will need
15 mm deep socket
3/8-inch extension and ratchet.
1/4-inch socket set.
Early-model Chevrolet truck ignition switch systems are complex. The key lock and tumbler on the side of the steering column drive a rod that moves the ignition switch contacts. That's OK, but the actual ignition switch is mounted several feet away on top of the steering column beneath the dash. Not only that, the dimmer switch, mounted along side the ignition switch, is also activated by a long rod. Do not confuse the ignition and dimmer rods..
Disconnect the battery to prevent ignition short circuits. Lower the steering column by removing the 15 mm column mount bolts. The column will drop safely down and the steering wheel rest in the seat.
Place the trouble light in a secure area under the dash and locate the ignition switch. The switch will have two black connectors that should be snapped firmly in place. The switch is easily recognized by the wiring harness that will have larger orange and red wires than other connectors. These are the main power supply wires. Carefully unplug the two connectors. Do not confuse these connectors with the lighting connector. The lighting connector is much longer, flat and does not have any large, power wires.
Locate the small, round, dimmer switch with a rod going into it. Leave it plugged in, but disconnect the mounting screws. The ignition switch shares a mounting screw with the dimmer switch. Remove two additional mounting screws holding the ignition switch in place. Gently pry out the switch rod that runs the length of the column to the key and tumbler.
Install a new switch by fitting the activator rod, mounting the new ignition switch with the screws and plugging in the wiring harness. Install the dimmer switch with the shared screw. Remount the column, attach the battery cables, and check the repair by starting the vehicle.
There is a slight amount of adjustment needed for the ignition switch. When installing a new switch, it is best to set the adjustment to minimum switch travel.
Many mechanics have confused the activator rods only to bend and destroy them. Pay close attention and work slowly and patiently on this project.
Jack Hathcoat has been a technical writer since 1974. His work includes instruction manuals, lesson plans, technical brochures and service bulletins for the U.S. military, aerospace industries and research companies. Hathcoat is an accredited technical instructor through Kent State University and certified in automotive service excellence.