I have looked and have found a few posts with similar issues but they are older cars and there was really no conclusion as to what the problem ended up being. The number 4 fuse in my '97 E420 controls the turn signals and the reverse lamps. When there is a good fuse, I can start the car, shift quickly past reverse and into drive and everything is fine. The turn signals work and I get no error messages. If I shift into reverse and leave it there for more than about a second the fuse blows out and I get the bulb failure message. Of course the reverse lamps and turn signals won't work because the fuse is blown. I am gathering that there has to be a short somewhere in the system. I tried taking the bulbs out of the reverse sockets, but the fuse still blows. I tried pulling away as much carpet as I could and looked at the wiring and can't find any problems in the wiring (there is quite a bit of wire that is not acessable with out major dissasembly). I have heard about people having problems with their neutral safety switch, but it seems like they don't have an issue blowing fuses. If anyone can help I would appreciate it.

Check if anyone felt like playing around with the wiring harness by the taillights. Seems like the only likely cause, especially if you have isolated the issue to just the reverse mode.

Are you the original owner of the car? If not, it's not unlikely that the PO didn't understand the bulb-out indicator, and may have done some creative wiring.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Check to seee if there is any evidence of melted lamp sockets in the rear holders.
210 problem.

I am the second owner. I have had the car for about a year and a half, with no real electrical problems. I checked the wiring harness that connects to each of the reverse lamps and they are both stock and in good condition. I can see no evidence of any melting sockets or anything else for that matter. Does anyone else have any ideas of things to check? What's the best way to isolate where in the line is a ground? Does anyone know the specific path that the reverse wiring takes start to finish. I looked as best I could from the back of the fuse box and down the side of the car and in the trunk lid.

Somewhere along the way the wire goes into the safety switch on the side of the trans.

I was told that the safety switch on this car is connected to the side of the shifter under the shifter console trim. Is this correct? What tests can I run to see if the safety switch is bad or if there is bad wiring somewhere?

The switch could be under the console. That is a better place than on the side of the trans where it was for years.
Pull the fuse and use a multi-meter to check the center contact in the reverse light socket for continuity to ground. There should be none. Move the shifter to reverse and check again. That should narrow your search.

try looking at the wiring harness in the trunk where it might be tied to the deck lid hinges.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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TRY to find the reverse OR some call it the backup switch, I do not know if it is on you transmission or located at the console ware the linkage and the shift lever meet. Try to find it and unplug it you may have a short in the switch,The only other thing is to trace wires or use the meter to see if you can find the short as Dave said.JNT

Well, after extensive testing with my ohm meter I narrowed down the ground out to somewhere in the socket cluster of the left turn signal. I removed the entire cluster, tinkered and looked it over while not really finding anything. Upon testing it while it was out of the car, I discovered there was no more ground out. I reassembled everything and it works fine now. I'm not sure what I did while I was pulling and looking at the different metal sections in the cluster, but it is fixed now. Hopefully it stays that way. Thanks for your help guys.

Now to tackle the new ASR/ABS light that just started coming on randomly.

There is no more neutral safety switch in the old style. There is one big switch S16/10 in the shifter console itself, and there is a back-up lamp switch S16/10/s2, but I don't know exactly where it is.