nelson480

Where do i start?
This car is a nightmare. Electrical problems up the ying yang!
First is the headlight.
passenger side is Dim, only 7.5 Volts, it runs both hi and low beam filaments at the same time. Checked all grounds it is short + not negative, so ground is not the issue. I tried inspecting the harness all the way to the block by the firewall. Fuse only 7.5 volts inside the car, pulling passenger HL fuse does nothing, but pulling driver HL fuse kills both. Turning high beams on works, then back off they will go to low beam but hi beam indicator in dash stays on, then service icon with wrench comes on. They function normally with the passenger headlight unplugged, no service light. DRLs work, unplugging resistor does nothing. Still dim also on DRLs. Hazards will not work also. Messing with the high beam also trips the dome light inside the car to come on occasionally, and ive even seen the trunk open once without touching the release.
BCM has been replaced brand new and programmed by dealer. Car has 155K miles.
Second issue is the radio. Will not turn off when key is removed and door opened. Switch for driver door is faulty, but wont turn off still if any other doors are opened. Switches confirmed working in other doors. This is a base model car, not PL, PW etc.
Thanks in advance, I dont know what else to do! I was going to try new multifunction lever, but wanted insight first.
Thanks again!

EinST

2005 Cavalier? I hope the BCM wasn't replaced for the headlamp issue. I don't quite understand what you mean by "Fuse only 7.5 volts inside the car." How did you measure the voltage, on which fuse and was it with the fuse in place?

The thing is, both filaments are tied together on the positive side with these headlamps. The ground side each gets spliced together with the counterpart from the other headlamp and goes to the MFS switch. The switch then grounds the appropriate circuit to turn on the lights, both sides. I think what's happening is that the passenger side headlamp is getting the battery voltage on the ground side of the high beam filament and the normally common positive side is wired to the high beam ground circuit to the MFS, i.e.:

Terminal A low beam ground
Terminal B should get battery voltage but now high beam ground
Terminal C should get high beam ground but now battery voltage

So, the current flows through both filaments in series with the low beam on. Both sides should be the same at the headlamp sockets and thus you can compare and verify.

On the fuses, it sounds like the passenger side headlamp is powered through the driver side headlamp fuse. You'll need to correct that since the wiring is not designed to carry double the load. I don't think you need a new MFS.

On the radio, what kind is it and have you checked the wiring behind the radio? It sounds like you may find a rat's nest back there. Yours may be victim of kiddies playing with the wiring.

nelson480

Taking a reading from the fuses: drivers side 12V, passenger 7.5v
Yes the BCM was replaced as a hopeful remedy for all the issues.
What can I do? I've seen MFSs cause all sorts of headlight issues, not dim ones tho.
Where are all the relays? Can't find any headlamp relays at all, and most GM cars have the maxi fuses for the headlights, why doesn't this car? And if it's not the MFS why won't the hazards work but the turn signals work, it's thru the same relay for both.

As for the radio, we are the second owner of the vehicle, and it's the original radio. It will turn off after 15 mins, but forgetting to turn it off via power button (clock stays on) will kill battery.

EinST

It's counterproductive to dwell on how it is with "most GM cars." If what I posted so far don't make sense to you, it's probably best to take it to a shop.

About the only way you could see 7.5 at that fuse is if it's blown and you measured the downstream side of the junction, i.e., the one that goes to right headlamp terminal B, with "right" being "passenger side." If so, you shouldn't see any voltage once that headlamp is unplugged. Then, the wire from right headlamp terminal B is intact but probably spliced onto the MFS high beam circuit as the same time.

So, trace the wires and troubleshoot along the line of what I think is happening:

Right headlamp terminal C: disconnected from the MFS high beam circuit but spliced onto the circuit between the left headlamp terminal B and LT HDLP fuse -- need to undo the splice (splice T becomes - and |) and then splice it back onto the MFS high beam circuit.

Right headlamp terminal B: spliced onto the MFS high beam circuit -- need to undo the splice (splice X becomes parallel =), replace the fuse, and then verify battery voltage at the headlamp socket terminal B plugs into