Help! weird electrical issue driving me nuts.

Hi All- I posted regarding this earlier, but things have unfolded and I'm looking for help.
got a 2006 passenger sprinter, 150K miles on it.

Upon starting up with the key, things intermittently go completely haywire, once the break pedal is pushed, the turn signal is turned, or the hazards are turned on- generally the engine cuts out, or restarts, or all the idiot lights come on in the dash.

I have taken it to the dealership twice, first they told me the isolated it as a bad break pedal switch, and replaced it. no sooner had i gotten out of the dealership, turned the turn signal and all went buggy again. I took it back in- they said bad instrument cluster, and so i shelled out to have that replaced, only to have the issue happen again. Im hesitant to take it back in, both because they keep charging and not fixing, and also they are a PIA about timing, etc.

Last night i was playing with the cable assembly right to left of the break pedal- and i found i could cause the same issues to come up just by jiggling the wires- my guess is there is a loose connection causing cluster confusion however Im not certain how to isolate it or what could be the point- none of the wires look worn or frayed. Do you guys know if it may the black plug connection that cluster of wires go too (looks like it ties into the fuses) and if so, are those replaceable? or might it be the cluster of wires themselves?

any help as to what to be looking for is appreciated- before i take it back in and shell out more money i want to see if at minimum I can isolate the issue before getting told its something altogether different.

thanks so much!
Matt

I can't answer your specific questions.

Initially I was going to comment that the rear light assemblies have some history of shorting and creating odd problems. Then you mentioned the harness wiggling which would not support that as a possible cause.

I will say that the Fuse Block #1 FB #1 under the steering column has some history of contributing to intermittent electrical faults. My turn signals were intermittent and responded to harness wiggling. They returned to normal after I removed the FB #1 to inspect/tighten connections.

I do admit that the symptoms did return some years later and required another go at FB #1. The FB #1 is available for about $100.00 and comes with a full complement of fuses and relays. Well worth the money for most people.

Some FB #1 info is here.

https://sprinter-source.com/forums/showthread.php?t=7909

This reply is intended as general information, not a diagnosis.

vic

In addition to Vic's suggestion, you might take a good look in 2 other places. Under the drivers seat inside the van, and under the van itself where a big bundle wiring goes out through the floor. Rodents seem to find the taste of German wiring irresistible. Look for signs of rodent damage. Good luck.

Matt.
My guess is that the brass nut embeded in the switches at the top of the fuse panel has been torn out by some heavy handed person. The connection between the fuses and the switches relies on this screw. To test this theory push the top of the fuse panel up into the switch assembly, if that fixes it remove the fuse assembly and repair the nut, Eric.

Some info on the fuse board and the how to pictures...


http://www.mercedes.gen.in/WP35/unsual-intermittent-power-problems-mercedes-sprinter/

All the best
Steve

Slight diversion from your current fault finding but a poster on my site had similar issues to yourself with indicators and brake lights caused by the trailer module. I wonder if you have a tow bar fitted and a trailer indicator module installed some where.... worth posting just in case but probably unrelated.

''I have a 3500 one ton dual , 2006 .
I had the same issue with the turn signals working
fine until you apply the brake, then they stop flashing,
and partially light.
I replaced the relay first, no change.
Then I cut out the converter for hitch wiring!
Work perfect now…just need to replace the convertor
for the trailer lighting.
Hope this helps''

All the best
Steve