1991 Buick Park Avenue 6 cyl Front Wheel Drive Automatic 187000 miles
At first, sometimes the headlights would not work when dimmed. Sometimes, shutting the hood or hitting a bump would cause the lights to work. Sometimes, holding the dimmer switch halfway makes them work. Now, the headlights stop working all together a little while after starting to go someplace. How can I make them work?
Hi troy91123. Welcome to the forum. It sounds at first like there's two different problems based on the symptoms and observations, but I suspect you'll find everything related to overheated terminals in the dimmer switch connector, which I believe is on top of the lower steering column, or burned switch contacts inside the switch itself. If the wiring in the connector appears to be ok, replace the dimmer switch. If the terminals in the connector are black or discolored, they can be cut out of the plastic and new terminals can be plugged into the switch separately one at a time. The wires will also be hard to bend in the first three or four inches indicating that part got hot. That section should be cut off and discarded, then a new section should be soldered in. Usually that will involve only two or three wires out of the many in the connector. Any wires that are replaced should have the splices soldered and sealed with heat-shrink tubing. I use crimp on type terminals but I solder them too to insure a solid mechanical and electrical connection. When replacing wires and terminals, the switch should be replaced too since that's where the trouble all started.
If the dimmer switch appears to have no signs of overheating, look for the same problems with the headlight switch connector. They also have an internal self-resetting thermal cutout, (circuit breaker), but based on your observations about hitting bumps, I'd suspect the dimmer switch is more likely the problem.
Normally I would recommend using a test light or digital voltmeter to isolate the problem while it is occurring but that is unnecessary if you find evidence of overheated terminals.