Viermalvier.de, das Geländewagenportal Foren Marken talk Mercedes Help! Problem with diff-locks

Guys,

Firstly my apologies for writing in English but my German is very basic. <img src="http://www.viermalvier.de/forum_php/images/graemlins/blush.gif" alt="" />

I have a 1991 W463 300 GD.

Today, I got a problem with my diff-locks. The thing is that it all started when I replaced the bulb of the front difflock switch. Every thing went perfectly until this evening when I went to the car to test that all the switches had their lights functioning. With the engine off, I put the parking lights and saw that all of them were functioning. But then I checked that the yellow lights of the diff-locks did also function -like I said without the engine running- they lit OK but then I put the light switch to "off" and nothing happened. All the interior lights remained functioning, including all three yellow lights, until I press the button of the difflocks to unlock them. Any of them would make all interior lights to go off.

Problem is that everytime I put the lights on, all three diffs attempt to get locked. Naturally, I cannot drive the car in these conditions (at least not during the night). Again, the only way to have the diffs unlock is to switch the lights off and then press the switches to unlock. Any attempt to unlock the diffs with the lights on is useless. Having the engine running does not seem to make any difference.

Anybody can help? Mercedes garages around here are totally hopeless in anything GWagen and I don't know where to start from.

Needless to say that this is very urgent.

Regards,

Mistery....

I went out again and put the parking lights on (without the engine running) with the key in the lock. All customary dashboard lights were on, plus the three yellow for the diffs and the danger sign (triangle) on the speedo which signals the diff locks on. Then I switched off the lights and all lights inside remained alight. Got out of the car and walked around it. No lights, except for those of the rear number plate (????????). then opened the passenger door and went to check the fuses in the footwell. After a while and without a warning all lights went off while I noticed a click somewhere in the relay tray beneath the fusebox.

After that went again to the driver's seat and but the lights on and off three or four times. No more yellow lights of the diff locks.

My only guess is that time limit relay of the difflocks is faulty (this is a pre-February 1994 truck).

Gosh, these are the beauties of electronics. In the good old days when a bulb wnet off it would never work again. You knew it was wrong. But now with these electronics you never know. This is just about the only bit of the 463 that I hate.

Regards,

sounds like you shorted some wires when you exchanged that bulb.
I would check that first.

Hello,

I hope that my english is so, that you understand what I mean.

At first i will also have al look at the wirring for the differential switches.
Then i will take out and disconect the switches for the differential locks and test the light of the car.

If this is not the right way, then i will take out the time relay for the differential locks, so the hole circuit ist out of order and you can see what will hepend now.

Greetings

Thomas

Went for a test drive. All three diff locks worked perfectly. Then I put the lights on an locked all three diffs. Then tried to unlock them (with the lights on) but they wouldn't disengage. Then I switched off the lights and the diffs would disengage at the first touch of the button. The problem is that, when I tried to recreate the problem it would not resurface again (after many attempts).

Anyway. It was clear at this point that the problem (inability to disengage the diff-locks) would only occur with the lights on so it more than likely that the cause was a short circuit that I inadvertenly created when I refurbished the difflock switch. This opinion is shared by almost everyone (thank you guys for your help).

But since I was unable to buy a new switch on a Sunday afternoon, I decided not to let a 40 pence electric bulb beat me and I have dismantled the switch again and redone the connections this time in a more thorough manner which I hope will work. I have retested the system again and all seems to work perfectly.....


Many thanks to you all,