Mercedes-Benz Forum banner

Fixing electrical problems

2K views 14 replies 9 participants last post by  TopHydraulics 
#1 ·
Hi SL owners, since my recent purchase I've been reading and Learning a lot about the R129.

And YES I have use the search fonction :wink A lot of good readings. Your forum is better than Fchat for this fonction.

Today I took almost everything out of my way to get use to my new car and see where are all the electrical and hydraulic boxes and controls.

I now understand why these cars were so expensive, they are a real mechanical piece of art and engeneering. Absolutely stunning.

My first concern was my passenger side power window that wouldn't go up. Looking at the switch I understood right away by the wire size that they were controled by relays. But to make sure I opened the door and checked the motor operation which was OK.

So now had to find the relays which bring me to the complete take apart of the car for my Learning. I love that part:grin

Found the control box Under the rear right seat and tested from there. Direct power to the big green and black wires my window worked as it should. So lets open that box!!!

Lift the cover, undo the 4 corner screws, remove a little metal lock piece in the large connector and slide up all this out of the case. Then carefully unfold the two printed circuit away from each other to reveal the Inside components including the relays.
 

Attachments

See less See more
5
#3 ·
I didn't check the continuity but I thought at first sight that the 4 bigger relays were for the power Windows. Looking closer at them I found one had no more spring for the moving tab. It had broke and fell out. Closer look showed the other big ones are also streched and will probably fail soon.

I will use used Bosch type relay and take the springs in them to replace those. I hope it will work. I will keep you updated with my results after it's done.
 

Attachments

#5 ·
#7 ·
I replaced the little springs with new ones. The silver one are from used relays and they are now rare I realized today. The new relays all have leaf springs instead I even checked a Bosch. Seimens were also leaves. The one I used were in a Hamann. The two others(black) are from a spring variety box.

Anyway, I cleaned the entire box with contact cleaner especially the relay contacts. Put the box back in place and test it.

BINGO it's working right, my passenger door window now go up and down.
 

Attachments

#15 ·
It looks like the steel springs broke where they were touching a dissimilar metal. Add some moisture, and they will rust easily in that spot.

There are no solid state window relays in R129 controllers; they only went to a miniaturized relay design starting with model year 1995. The miniaturized relays are a pain to get out of the circuit, but at least one forum member has replaced one of them before with an off the shelf item. I don't think he gave us the p/n at the time.

The main problem was by rust of the springs and only those four. I guess the heat may have help enhance it.

If I was to have problems again with those I would just wire them out of the box with regular relays.
Yep, the heating and cooling in the module and near the relays would accelerate corrosion, as long as there is some moisture in there.

Right on, two standard 5-pin DPDT relays per window, wired in externally, would do the trick if anyone finds too much damage on their board mounted relays.

Klaus

www.tophydraulicsinc.com
 
#13 ·
Nice write up and result, very well done


I used to once be a Radio and Television engineer, and our workshop manager would make us re-wind transformers, relays etc. That ethic has always stayed with me until this day.

I never throw electrical kit out, and often remove transistors, capacitors etc. from old circuit boards to keep other things running
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top