Hi all,
Long time lurker, first post. After looking for several months I finally bought the car I wanted since my youth - a R129. I opted for a fairly low mileage (90K) 300SL 1990 5 spd auto in arctic white with chrome factory 16" wheels for a pretty good price, knowing I was getting into some work going in to make the car what I want it to be. The car has a well documented service history. I'm a powersports tech by training and trade, so I'm no stranger to turning wrenches with 17 years at franchised dealers under my belt. I'm also pretty good with my Fluke meter... This car was purchased to be a daily driver (except for NE winters) like every one I looked at needs the hydro top system rebuilt. That's this winter's project, if I can source the parts I will refurbish the rams myself. I opted for the I6 for lower maintenance costs and after a full tune and service it runs like it should.

So the only problem I haven't been able to sort thus far is the brake lights quit working. The warning lamp came on and got brighter when I stepped on the brakes. I first tested the stop lamp switch switch, shows .3 ohms or open when depressed or released depending on the circuit or 1/2 of the switch tested - appears good. With the key off or on it is missing the 12v supply to the switch. The fuse is good. I even cleaned the connections in the whole box just to be safe. I have the star ETM but can't get the diagrams to open. Does anyone have the wiring diagram available for the exterior light circuit? Trying to back trace the power to the switch and determine which relay is involved.

Any help or input would be greatly appreciated!
Thanks,
Tom Merlau aka bikebitzofvt

P.S. Also looking for a overhead console housing and a side skirt jack point plug and new roller doors for the cassette tape/lighter box for reasonable money...

 

I fixed this today after some searching & head scratching. I found a fried circuit inside the light monitor module (PN 1295420132) I was able to repair the box but I couldn't find a definitive cause for the failure.

 

Hey Tom,
Name's Chuck. I, too, have been a lurker until now. I recently bought my wife a 1990 R129 500SL, and although I got a good deal on it, it needs some help in a few areas. The priority problem I have now is the same you had, I think...no brake lights. Where exactly did you find that light monitor module? I'm a do-it-myselfer, however I learn usually by trial and error...lol. Any help would be appreciated. I'm hoping it's similar although you have the 300 and I the 500. Brake lights are kinda important, as my wife would say. Thanks.......Chuck

 

Klaus at TopHydraulics does a great job rebuilding the cylinders for about $55 each. I had all 12 done for $550. Figured might as well do them all at once.

 

@ Chuck - the box was under the hood - passenger's side near the firewall. There is a cover that comes off to access the slew of control modules. IIRC the light monitor box was in the center. If you haven't gotten one yet I highly recommend getting a DVD manual, if only for locating components.


The box unplugged from the harness and was a simple affair to open up - a small screwdriver to pop the cover off. There was an obviously fried resistor, I broke out the soldering equipment, removed the bad one and soldered in a new one - at the cost of less than a dollar. The control module new is about $450! I never did find the cause of the failure but the repair has worked fine since.


@Scott: I'm planning on sending Klaus my rams here soon for rebuild - all 12 - once the garage bay is vacant and I can leave her in there torn apart for a while.


The only other thing on the agenda is struts. My front struts are the originals and have an aluminum body!?! All the replacements I can find seem to be steel. Does anyone have some input??