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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / January 2006Lost headlights and inst. cluster lamps
Bizarro problem here. Vehicle is a 90 Grand Prix. Everything was fine yesterday, then today no headlamps, running lamps, or instrument cluster lamps. Fuses OK, voltage at fuses. My Haynes manual doesn't specify a relay in line with anything, but when the switch is moved to the parking or headlight positions I can hear a relay click. Before I start tracing wiring, anyone had this issue? Could be a ground connection gone bad. On a GM, the main body ground is a mesh strap from the bell housing to the body. The secondary one is from the battery negative to the fender. I have seen the mesh one go bad and everything run off the small secondary until it melts and pops. Sometimes the vehicle can still steal enough ground to still run through the gas pedal cable or shifter linkage... The power for the headlights comes from a fuse link wire on the starter solenoid. The running lights are fused usually though. Switches do go bad too. If you can get your hand up there, feel for melt damage on the plug top center. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) > Bizarro problem here. Vehicle is a 90 Grand Prix. Everything was fine > yesterday, then today no headlamps, running lamps, or instrument [quoted text clipped - 3 lines] > start tracing wiring, anyone had this issue? Could be a ground > connection gone bad. On my 95 Lumina, I had bad connection at the right rear Stop Lamp. My tail lights and turn signals worked fine, however, the stop lamps did not operate. This was again one of those "failsafe," problems, in that it notified me of the bad circuit by extinguishing my dash lights. Still investigating this stealing ground scenario. When Mike mentions "steals enough ground," this, electrically speaking says that a "good" ground has been compromised and that now a "ground side voltage drop" exists. This results in lower circuit current. Just how these digital dashes monitor the circuits invloved, and how they respond is pretty much model specific and, again, rarely if ever outlined in publications offered to the public. I suggest always comparing ground side voltage drop readings with the meter connected to the circuits' ground, and then with the DMM grounded at the battery terminal itself. Doing this will check the integrity of the circuits ground, and relieve you from troubleshooting phantom grounds. The fact that the relay clicks means that it is getting acuated. The fact that it is affecting the entire lighting system would point me start troubleshooting at the ouput of the relay that is being acuated. Jim Sure sounds like the switch to me. All the light functions you listed as not working all have the switch in common and different fuses and wiring. Update: The switch was part of the fault. I took it apart and found a broken support tab for the running lamps section. Swapped the fog lamps contact (which never got used anyway) for the running lamps contact. Thats OK now. Still no lamps tho. I have 12v at the connector for the switch, but get nothing at the fuse block for the inst. cluster. According to the Haynes manual (spotty wiring diagram), the headight dimmer is in line with everything, so if that fails it will take the rest of the lamps with it. I still need to check the wiring to-from that switch, but the park/neutral switch failed some time ago so it looks as if that's what I have. If its going to be as much of a PITA as the P/N sw was to get at and remove (which I didn't, I rebuilt the circuit entirely with new wiring and relay), I'll wire in an outboard switch somewhere. Good thing I have the Fluke insulation piercing probe...... |
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