300 TE (W124) rear wiper woes

[rjk]

I've been slowly fixing up the 300 TE I bought for my daughter earlier this year and I've run into a head-scratcher. The rear hatch seems to have an electrical gremlin in residence. Here are the symptoms I know about:

wiper runs VERRRRRY slowly, if at all.
upper brake light is on dimly but goes off when I hit the brakes (regular brake lights work fine)
upper brake light will intensify slightly when the rear wiper is switched on
relay mounted in hatch buzzes when I turn on washer but washer does not squirt

Am I looking at a new relay? A short somewhere? Where should I start? I figure to at least resolder the relay board assuming it could have the same problems as Bosch/Volvo relays.

R&R of the flex connectors (driveshaft) went smoothly but there was an anomoly. The website called for different front & rear connectors which came as listed. The front(?) one looked heavier and had thick, odd looking washers while the rear(?) had round, thinner washers. When I dropped the old ones out, they were both the same right down to the molded-in numbers. Did a previous mechanic take a shorter/easier/cheaper way out? Is this why my rear connector was shredded? Which connector is correct for the tranny and which for the diff.? I currently have the heavier conn. on the front/tranny union and the smaller on the rear/diff.

I'm looking at a rear main seal replacement, how big a bear is dropping this tranny? Straight forward, or should I be aware of any "special" items?

[Greg in Oz]

It is very likely that at least the chassis-ground wire in the tailgate wiring harness has broken. This happened about 12 months ago in our 300TE. First symptoms were interior lights in rear became intermittent with position of tailgate when open.

I removed the roof lining at the rear to gain access to the wiring harness for the tailgate. By pulling on the wires individually I was able to find the broken ones (when they pulled free). The break occurs where they flex with the opening and closing of the door. In our case the chassis-ground (brown wire) was broken as was that for the rear demister (black wire). These were the two thickest wires with the thickest strands which least like constant flexing.

By removing the harness at the roof end and sliding off the rubber sleeve that fits between the tailgate and body I was able to splice in new wires to replace the broken ones. For each I used two runs of thinner wire which matches the original current carrying capacity but better handles flexing. Whilst it was a fiddly and time consuming exercise, it saved me the considerable cost (and also fiddly and time consuming job) of replacing the wiring harness with a new one.

[rjk]

Nice call Greg!
You nailed it right down to which wires were broken, except I have a third small gauge wire broken too.
First, I jumped a grounding wire across to the tailgate and lo and behold, everything seemed to work normally. So I did what you suggested and bingo, 3 wires parted. Now, if I can just figure out how you got the grommet off, I'll be home free.

[Greg in Oz]

Originally posted by rjk
Nice call Greg!
You nailed it right down to which wires were broken, except I have a third small gauge wire broken too.
First, I jumped a grounding wire across to the tailgate and lo and behold, everything seemed to work normally. So I did what you suggested and bingo, 3 wires parted. Now, if I can just figure out how you got the grommet off, I'll be home free.

I can't remember if there was any trick to it. It was a very awkward job though. I remember spending a good part of an afternoon fixing it. It just takes perseverance. Good luck.

[ke6dcj]

Next on my list.

:-) neil

[ke6dcj]

Originally Posted by ke6dcj

Next on my list.

:-) neil

Done. Three wires total were shot.

I used some liquid dish soap to get the rubber boot back onto the liftgate, but I couldn't get the rubber boot's lip back onto the body. Any tips ?

Took me about 3-hours to do from start to finish.

Pulling back the rear window rubber surrounds took a LONG time.

:-) neil

PS: I'm going to fix this harness, and maybe put it up for sale.

[locry]

hmmmm... would any of you know where the trigger is for the rear lights when the tailgate is up?

i can turn on the rear lights with the switch upfront... opening the tailgate doesn't light up the rear convenience lights... yes...i've tried ALL the switch settings... no go.

thanks

[BENZ-LGB]

Originally Posted by locry

hmmmm... would any of you know where the trigger is for the rear lights when the tailgate is up?

i can turn on the rear lights with the switch upfront... opening the tailgate doesn't light up the rear convenience lights... yes...i've tried ALL the switch settings... no go.

thanks

Judging by the action, I would guess that the switch is either in one of the hinges (so when the door comes down, the action of the hinge moving back into the body triggers the light switch) or the switch is in lock mechanism (and it is triggered by the "handshake" that closes the gate).

You, however, had probably made the same guess.

[locry]

it may be in the lock mech coz i see no sign of an electrical switch/contact anywhere near the hinges...

anybody with a working system care to experiment? when exactly do the lights turn on? when the hatch is raised or immediately after the locking mech disengages?

[david s poole]

the rear lights [inside]are supposed to turn on as soon as you press the button to open the hatch.