Diagnosing GM Converter Lock-Up Problems

Test #2

Checking For 12 Volts Across Fuse

1. Check for 12 volts at both sides of the fuse.
2. Locate the fuse box and the fuse marked "gauges" (most models).
3. Connect the alligator clip of your test light to ground. Turn the ignition on.
4. Place the tip of your test light on one side of the fuse and the tester should light.
5. Place the tip of your test light on the other side of the fuse and the tester should again light.

Test #3

Checking For 12 Volts Across Brake Switch

IMPORTANT: Either of these switches can be used for lock-up. To avoid mis-diagnosis, check them both. If the upper switch with the vacuum hose is used, check the two wires at that switch. On the four wire lower switch, check the two wires farthest from the plunger.

1. Check for 12 volts at both sides of the brake switch. Some GM vehicles have two electric switches at the brake pedal. One switch will have four wires and the other switch will have two wires and a vacuum hose.
2. Connect the alligator clip of your test light to ground.
3. Do not depress the brake pedal.
4. Turn the ignition "on".
5. Push the tip of your tester into one wire and the tester should light.
6. Now test the other wire and again the tester should light.
7. Depress the brake pedal and re-test. Only one wire should now be hot.

Test #4

Adjusting/Replacing the Brake Switch

1. Remove the brake switch from its bracket.
2. Reconnect the wires to the brake switch.
3. Re-test as stated in test # 2, but push and release the plunger with your finger or thumb.
4. If it now passes the test, the brake switch is good, but needs adjusting.
5. If it still doesn't pass, replace the brake switch.

Test #5

Checking Wires For Shorts and Opens

IMPORTANT: Make sure the ignition switch is "off" for the following tests.

Shorts:

1. Set your ohmmeter to ohms times one (Rx1).
2. Connect one lead of your ohmmeter to one end of the suspect wire.
3. Connect the other lead of your ohmmeter to a good ground.
4. If the meter reads ANYTHING other than infinity, you have a short to ground in that wire.

Opens:

1. If a suspect wire has no voltage through it, and its connection at both ends is good, and it's not shorted to ground, the wire has an open in it.
2. Replace the wire.

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