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1992 745 Central Lock Fuse 2 keeps blowing

chronicrhythm

Member
Joined
Sep 28, 2012
Location
Colebrook, CT
I just got a clean 92' 745 and am trying to fix a few issues so a friend can take the car. One issue is that the Central Lock fuse 2 keeps blowing when I go to unlock the car. I have read that I should check the drivers side door panel and check for frayed wire which I will do but I am also having an issue with the hatch lock. The key won't turn the lock cylinder at all. It seems stuck and I had to take the back panel off to flip the lock so I could at least open the hatch from the outside. I'm wondering if the frozen lock is causing the fuse to blow and if so, how can I make the lock turn?
 
Lock mechanism uses electromagnetic solenoids which generally don't use any extra power when mechanism is stuck. So the frozen cylinder is unlikely the cause of your issue. Almost certainly it's a wire shorting to ground that's blowing the fuse (or less likely, some kind of weird relay failure). Not much you can do other than go through with visual inspection and/or multimeter on each of the door harnesses to find the short. Perhaps someone else can chip in with recommended places to check and what to look for.

As far as the frozen lock core goes, I'd try lubricant (if you use wet to unstick it, make sure to clean out with solvent and apply dry lock-friendly lube after). If that doesn't fix it with some jiggling, you're probably gonna have to either take the stuck one to a locksmith that can hopefully disassemble and clean/fix it, or get a replacement from somewhere and get it re-keyed to match the old. (Keep the old lock - if the pins are still in good shape they can be used to easily and quickly key the new lock.)
 
Check to see if your car uses a master key or a valet key. On my 240, the valet key will only open the door and turn on the key. If it has the correct key, break free is a good lubricant that can help free up the lock. Coat the key with the lubricant and let it sit in the lock for a while then gently wiggle it back and forth to see if you can un-stick it.

The door wiring for the solenoid is most likely stripped of insulation. You can try to repair it with heat shrink and or liquid electrical tape. Mine was heavily corroded and I wound up removing the wiring to the door locking mechanism as well as popping out the relay. Before doing this, you can do a visual inspection of the relay terminals and socket for corrosion/ heat damage. You can also pop the top off from the relay to see if there are any broken solder joints.
 
Check to see if your car uses a master key or a valet key. On my 240, the valet key will only open the door and turn on the key.

Good point. Some dealers can still cut you a new master key based on the VIN I think.

Relay is worth inspecting but is probably fine. They tend to fail open rather than fail short.
 
Thanks for the replies everyone. I took the door panel off and checked the wiring. I didn’t see anything wrong and it seemed like the central locks started working. When I closed the door they blew another fuse so I did more inspection. The wires look great that go through the door and into the cabin. So I’m kind of at a loss. I think it might be a wire shorting farther up in the dash board
 
Check to see if your car uses a master key or a valet key. On my 240, the valet key will only open the door and turn on the key. If it has the correct key, break free is a good lubricant that can help free up the lock. Coat the key with the lubricant and let it sit in the lock for a while then gently wiggle it back and forth to see if you can un-stick it.

The door wiring for the solenoid is most likely stripped of insulation. You can try to repair it with heat shrink and or liquid electrical tape. Mine was heavily corroded and I wound up removing the wiring to the door locking mechanism as well as popping out the relay. Before doing this, you can do a visual inspection of the relay terminals and socket for corrosion/ heat damage. You can also pop the top off from the relay to see if there are any broken solder joints.

I think you?re right about the key being a valet. It also doesn?t open the glovebox. I never knew those existed.
 
Thanks for the replies everyone. I took the door panel off and checked the wiring. I didn?t see anything wrong and it seemed like the central locks started working. When I closed the door they blew another fuse so I did more inspection. The wires look great that go through the door and into the cabin. So I?m kind of at a loss. I think it might be a wire shorting farther up in the dash board

Did you manage to get a look at the section which runs through the rubber boot from the door to the body? That's the part that gets bent/abraded all the time and is most likely to fail. Especially the fact that it blew the fuse when you closed the door says to me that those wires are moving and shorting on something.

While I would continue to hunt it until fixed, there's no shame in unplugging the central locking temporarily in order to save on fuses.
 
Update:
I put another fuse in and noticed when I pulled the locks up that the rear drivers side door did not go up but the others did. I decided to investigate the wiring in that door and found a wire going to the lock mechanism had rubbed through on the metal of the door. Fixed that up and no more blown fuses but that door still doesn't work for some reason. I think having 3 doors and the tailgate work with the key is better than just one so I'm leaving it as is for now. Also before doing the rear door I went through the entire front door and didn't find any bad wires but discovered that this car does not have speakers in the front doors which I found interesting.
 
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