How the Ignition Switch Works

The original ignition switch looked to be in pretty good shape. All I was missing was a key. Now if you'be gotten this far then you know that I'm not going to pay a locksmith to cut a key for me. A lot of people don't realize this but keys are not as unique as you think. My friend Steve had a 71 Mustang and a 76 Pinto in the early 80s and his dad had a 70 Montego. Steve found out by accident that his Pinto key worked on all 3 cars. Most wreckers have a couple of coffee cans full of old keys, so off to the wreckers I went.

After about 10 minutes of trying out about 50 different GM keys and tolerating the ribbing and remarks from the other customers, I found a key that works like a dream. The best part is that the key was free and I got to rub it in to the astonished crowd (actually 2 high schoolers who worked part-time at the front counter for beer money).

ignition lock

Ignition lock with key!
(Digital camera just hates chrome reflections - makes it look green for some reason when its actually a metal grey body and chrome mounting ring)

ignition lock pinout

Ignition lock pin functions

I buzzed out the ignition switch and its pretty basic for the operation, just as I thought and no real surprises except for the ground terminal (GRD):

BAT   - Battery +12V from the battery
ACC   - accessories in key accessories position and run position
SOL   - starter solenoid in key start position
GRD   - Shorted to the case in the start position
IGN-1 - ignition/coil key run position
IGN-2 - ignition/coil key start position

ignition switch positions

Ignition switch positions

The two ignition teminals puzzled me at first than I realized that in the olden days, there was a resistor in series with the coil during the run position. While starting the engine, the resistor was bypassed or shorted so that more juice could hit the coil cause the battery voltage drops due to the starter load. So basically the coil series resistor goes between the two ignition terminals.

The ground terminal (GRD) just plain threw me for a loop. Why ground the case only during starting? I posted the question to the rec.autos.rod-n-custom guys and I found out that some vehicles check the idiot lights while starting. The ground terminal provided the ground that was required to turn on the idiot lights to see if the lamps were still working.

The chrome mounting ring for the ignition key has a green plastic ring which is used as part of the dash lighting. A lamp behind the dash provides the illumination so that you can see the outline of the switch.

If this page has helped you, please consider donating $1.00 to support the cost of hosting this site, thanks.

Return to



Copyright June 2011 Eugene Blanchard