I just finished work on my transmission and was going to do a flush. I hooked up the battery to start it and when my son turned the key sparks flew from the starter area. I went back to check the battery and I forgot to connect a small black cable to the + positive terminal (it was tucked behind the panel) now the car dash lights up everything works except the starter wont even click (1) what was that wire I didn't connect and (2) did I fry the starter (3) is there a fuse or relay to replace and where is it (I checked everywhere)any help would be greatly appreciated.


Thank You


Hi Pitner,

Sorry to hear about your troubles. Without a picture is it hard for me to remember what the black wire is for. It's been a few years since I sold my 1998 SL500. Maybe post a picture if you can.

With that said, I don't think the issue here is that the black wire was left disconnected. What happened is that a wire was shorted accidently. It seems that the wire that goes to the starter solenoid is shorted. When you turned the key and try to start the car, that wire feeds 12 volt to the starer. Check that wire becasue it is either exposed, connected wrong, or damaged.

Now the problem is that your car won't start and that's becasue you blew a fuse. Hopefully its just a fuse. Check the starter fuse and relay and go from there. That fuse should be in the engine bay if I remeber correctly.

I didn't think that you fried the starter. I just hope there were no further electrical problems were casued than just a blown fuse.

Let us know what you find out.



battery terminal



This is the battery terminal the small black wire is the one I forgot to connect when starting.

this is the fuse box engine right hand side, I checked all fuses and they were good.

This is the fuse box engine right hand side, I checked the fuses they were good.

This is the box engine left ,


This is the box engine left , I saw no relays or fuses in this box ( just the ones attached to the ECM) it was just wires unless I am missing something.

Trunk fuses

This is the trunk fuses all good. Is there any areas I am missing because I see no relays to speak of. I looked all over the net and I can"t find any place where i see a specific place for a starter relay, or starter fuse on a 99 sl500. I did drip some trans fluid in the starter area when I was filling the transmission.   Thank You MB






"I did drip some trans fluid in the starter area when I was filling the transmission. "

That is what did it. It shorted the starter solenoid feed to ground. One correction to MBFanatic. The R129 connect to the starter via the neutral safety switch. There should be an over protection fuse on the fuse panel as well sometimes refered to OVP fuse. Check that as well.

Take a minute and look at the wiring diagram here: http://www.bbbind.com/free-tsb/

Hi Guys, I am truely sorry but I did leave out that the work I did was a conductor plate change ( if that makes a difference). So I went to the fuse box and I cant find an over protection fuse and I cant find relays anywhere (pictures attached) I also see according to the diagram there should be a fuse . I believe the neutral safety switch is on the side of the transmission. does anyone know where the relay is or the over protection fuse is. I am at a lossfuse box dia 1fuse box1Dia 3

Dia 2


Considering the year, your model may be equiped with what is called the base module . It is known as N16/1 Base Module and can be found on the engine compartment, passenger side. It should be near the 38 pin connector. It should have three fuses in it that you should check.

MERCEDES R129 W140 SL500 S500 GM Base Control Module ECM Computer 018 545 81 32 The Base Module took over the function of over protection fuse somewhere  in the mid 90s.

See these two pdfs.

Base and Control Module_AR_AR54.pdf (68.0 KB)File Type: pdf

Base module Function_GF_GF54.pdf (26.8 KB, )

Make sure your car has it first. Check the fuses. Verify that in fact that is the culprit.

If you need to replace it a used one will cost arount $100 while at the dealer it will cost about $400-$500. It should not need programing. Here are some eBay listings: mercedes base module r129

Let us know how it goes.



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