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Old 02-19-2018, 02:22 PM   #1
burk992
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Thumbs down Central locking is frying the fuses

'89 245DL LH2.2 AW70

I can't seem to get to the bottom of this one. The number 8 fuse that controls the central locking and my dome light is continuously blowing fuses to the point that I just have not replaced them any more.

If it blows, the central locking will almost lock all of the doors if I push down, and if I pull up on the lock, it will try to fire the rest of them to unlock. The rest of the locks will kind of move as if they got the signal but don't have enough power to move.

If it has a new fuse in it, I'll be able to use the auto locks a couple of times with no problem before it gives up and blows the fuse. Don't really know where to start with diagnosing this one and I'm getting sick of not having a dome light because this has been a problem since last summer. If I could just get an idea of somewhere to start, that would be much appreciated.
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Old 02-19-2018, 02:28 PM   #2
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You always start in the drivers door. Gotta take off the door panel and look at the wiring. There is a three wire connector along the middle of the door behind the door panel. You can disconnect the door switch and the push pull button at that connector. A broken switch that is around the lock cylinder may be stuck trying to fire the locks. Corroded and fraying wires from that switch to the connector inside the door are shorting together. That kind of stuff is the most common. I've even had the clip that holds this little harness cut through and short the wires. The wires can also fatigue where they go through the door but most of the time it is the other above issues.
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Old 02-19-2018, 05:05 PM   #3
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Quote:
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You always start in the drivers door. Gotta take off the door panel and look at the wiring. There is a three wire connector along the middle of the door behind the door panel. You can disconnect the door switch and the push pull button at that connector. A broken switch that is around the lock cylinder may be stuck trying to fire the locks. Corroded and fraying wires from that switch to the connector inside the door are shorting together. That kind of stuff is the most common. I've even had the clip that holds this little harness cut through and short the wires. The wires can also fatigue where they go through the door but most of the time it is the other above issues.
Thanks for the quick response Dave. I'm pulling into the shop early tomorrow to work on a laundry list of stuff, but this is at the top. I'll report back.
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Old 02-19-2018, 05:34 PM   #4
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pay special attention to where the wires jump from door to A-post/body. This is the place where the wiring is subjected to the most mechanical stess (= door opening and closing) and where those wires have to pass through holes in the sheetmetal.
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Old 02-19-2018, 05:37 PM   #5
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You reminded me of another central locking problem I had. The lock actuator in the bottom of the door had a split boot on it and water was getting in there. The thing shorted internally causing continuous locking on the drivers door. As soon as you opened the door to get out you were locked out. Never mind the battery drain. I've seen the system draw 10 amps. lol.
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Old 02-19-2018, 05:42 PM   #6
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Expect to see this on your power lock accuator and on the key lock wires. It just needs some simple repair/replace of the wire.
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Old 02-19-2018, 06:09 PM   #7
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Quote:
Originally Posted by dl242gt View Post
You reminded me of another central locking problem I had. The lock actuator in the bottom of the door had a split boot on it and water was getting in there. The thing shorted internally causing continuous locking on the drivers door. As soon as you opened the door to get out you were locked out. Never mind the battery drain. I've seen the system draw 10 amps. lol.
I've lived this one as well..
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Old 02-19-2018, 08:17 PM   #8
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Quote:
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Expect to see this on your power lock accuator and on the key lock wires. It just needs some simple repair/replace of the wire.
Dave B
^ This is what mine looked like. Splice in some new wire, solder and heat shrink. Try to keep the same colors on the splice.The wires closer to the "black tube are bit harder. Once you get some good wire on there liquid tape works best.
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Old 02-19-2018, 08:54 PM   #9
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See https://forums.tbforums.com/showthread.php?t=322700
and https://forums.tbforums.com/showthread.php?t=323301

As a minimum, you can unplug the 3 wire connector (black/green/red?) to the door switches, located roughly over the driver's left knee, to prevent draining your battery and to keep the dome light working (but no central locking).
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Old 02-20-2018, 07:29 AM   #10
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Dead short to ground......when repetitive fuse failures occur, ask yourself why? Do you know Ohm?
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Old 02-20-2018, 09:15 PM   #11
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Update: Pulled the wagon into the shed this morning and went to give my dad a hand with some loading/unloading work before I started working on the wagon. Busted my face open and chipped my bottom teeth on a fifth wheel camper that popped up out of seemingly nowhere. Took an emergency visit to the dentist instead of taking the door apart! Tomorrow, I guess...
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Old 02-20-2018, 09:54 PM   #12
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I hope you feel better. That sucks when you are taken by surprise and hurt from it.
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Old 02-21-2018, 08:20 AM   #13
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Sorry to hear about the accident. Dentists can do wonders with new materials on chipped teeth, you'll hardly even notice later.

I did the central locking repair, no corrosion, just cracked insulation, easy fix
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Old 02-23-2018, 05:07 PM   #14
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Quote:
Originally Posted by dbarton View Post
Expect to see this on your power lock accuator and on the key lock wires. It just needs some simple repair/replace of the wire.
Dave B
I had the exact same problem on my 92 Model 240.
Cut and solder and shrink wrap are the fix.
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Old 02-27-2018, 10:55 PM   #15
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Hey y'all.

Unneeded update about my mouth: went back to the dentist, he didn't know if it was fractured or not so he drilled off the top of my tooth to see if there was a fracture that would open up enough to see on an xray. If there isn't, he'll fill it. If there is, root canal so help me god. My mouth hurts.

Anyway, today was 67F in STL so I ripped into my wiper motor because it was parking straight up and down. The ground wasn't touching the top cover and I cleaned all the contacts. Voila! No more ridiculous looking wipers.

Tomorrow, it's pretty likely that I'll finally dig in on the door wiring. While I have you all looking:

There's no difference between a DL and a GL door card, right? I have some massive speakers that I'd like to put in my wagon that I stole from one of the family's parts cars, but it turns out that the speakers are so big that the parts car's door cards had to be cut to fit. The parts car's interior matches mine so I figured I'd just switch them out.

I've also got a fried rear wiper motor that needs looked at. Got a lot of time on my hands since I graduated in December and am still jobless. Smh.
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Old 02-28-2018, 02:51 PM   #16
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about the rear wiper motor, check it on a seperate 12V source. It just might be OK.
cars with a tailgate often have issues with the wiring getting damaged (causing shorts) or broken (causing the component to stop being powered) near the hinge where it goes from body to tailgate.
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Old 02-28-2018, 07:04 PM   #17
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So we've got a winner! I got the door card off and the plug that goes from the bottom of the lock actuator back into the cabin is actually healthy. I looked deeper in the door and found that the key lock ... mechanism (does that have a name?) was the culprit. So I laid it out on the dining room table and started to clean on it a little bit and it just came right apart. I popped it open and there was no way that I felt like I could get wires back in there, so I went out back behind the shed into the parts sedan we have and took the key lock mechanism out of that car. It was not in much better shape as the insulation had dry rotted, but I cleaned it up and heatshrunk it and spliced it into the actuator harness.

I may have made it a little too long, and upon further examination on reinstallation, I did not lay the wires over back in the pattern that they were in on removal, so there might be some strain there. I also did kind of a ratchet job of splicing and dicing. Put it back in, and voila, power locks.

However, I now have power locks that lock when pushed down without blowing the fuses, but when I pull up on the actuator, only the passenger rear door slides up, the rear driver side lock slides up a bit and doesn't finish, and the passenger door does not budge.

I also must have reinstalled something wrong, because when I lock/unlock the door, it now has a lot of resistance to it. I dunno.

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about the rear wiper motor, check it on a seperate 12V source. It just might be OK.
cars with a tailgate often have issues with the wiring getting damaged (causing shorts) or broken (causing the component to stop being powered) near the hinge where it goes from body to tailgate.
That's what I was thinking about doing too, but that will be the next step after I finish up this problem first. The thing about the rear wiper is that for the past couple of months it was working intermittently - I would turn it on, sometimes it goes, sometimes it wouldn't. If I left the switch on, maybe I would get a few miles down the road and it would actuate a few times but then it would quit again for a while. Maybe the magnets on the inside came loose? Or a multitude of other things.
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Old 02-28-2018, 11:55 PM   #18
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1) The "new" door cards should fit. The only time the cards are different is if one has roll up window and the power window. But they will still fit.
2) The doors that do not unlock could have the lift motors binding.
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Old 03-01-2018, 11:31 AM   #19
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More fun. Got everthing buttoned up yesterday and went to the cafe my girlfriend works out to have some coffee (where I wrote my last post), and then when we left, got in the car, started it, and immediately my fuse panel started billowing smoke. Opened it up and the fuse was so melted that the copper was bright red.

Quote:
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I also must have reinstalled something wrong, because when I lock/unlock the door, it now has a lot of resistance to it. I dunno.
I wonder if I installed the key lock mechanism, I didn't seat it correctly and something stuck open when I unlocked the car door? Bout to eat some breakfast and rip into it again.

At this point I'd like to thank everyone who has posted in this thread because you guys have helped quite a bit. I'm not much of an electrician.
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Old 03-01-2018, 01:07 PM   #20
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Sorry for the double post.

Got the door card pulled off and gave everything a look, nothing is melted or anything. I put a new fuse in and tried both the outside and inside lock and when I pulled up on the inside lock for more than a second, immediately the fuse starts to smoke and goes, so I guess there's some extreme draw there. Is that indicative of the lock actuator being bad as well? Possibly a problem further up the harness towards the cockpit?
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Old 03-02-2018, 10:52 AM   #21
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You will now need to follow the wires into the rubber boot that connect to the body. First unplug the harness from under the dash or disconnect your battery.
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Old 03-02-2018, 10:10 PM   #22
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The central locking wires in the door shouldn't be able to smoke anything directly. There are 3 wires - a ground and two control wires that each go to the one of the lock/unlock relays. If you ground a control wire, it grounds that relay's coil and draws only ~0.1amps. This isn't enough current to smoke anything directly. Short the door wires to ground and it still can only draw ~0.1amps. You should be looking for something else, like another degraded wire, or a a shorted out door actuator on the other 3+1 doors+hatch/trunk.

[Following the wiring diagrams for central locking isn't easy. I'll try to describe how it works. All the actuators are wired in parallel. If you apply +12v to one side, and ground to the other side, they all contract and lock. If you swap and apply ground and +12v to the opposide sides, the actuators all expand and open. OK so far?

The locking relays, and relays in general, have a central flapper contact that switches between two other contacts. There's coil that moves the flapper when energized. Central locking uses two relays, one one per actuator side, with the flapper switching between ground and +12v. When un-energized, both relays flappers connect to ground. This grounds both sides of all actuators and nothing happens.

When one of the relays is energized, by grounding a control wire via the door switches, that relay flips to +12v. This supplies +12v to the corresponding actuator side and the actuator moves. Likewise, grounding the other control wire energizes the other relay and supplies +12v to the opposite actuator side. OK? I'll try to explain better if you want.]
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Old 03-02-2018, 11:50 PM   #23
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You can remove all of the door cards and test each actuator one by one to see if they do lock/unlock.
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