1990 300sl electrical issue - PeachParts Mercedes-Benz Forum

Hogweed · #1 06-09-2011, 10:05 AM

i've received limited response posting this in the sl forum so i thought i'd try here. please note: the turn signal lights are on, not the parking lights. several replies on the sl forum suggested the headlight switch in the 'safety' poition, which it is not.
problem:
i've owned this car for 3 years. bought it with 82k now has 86k. always runs well, never had any issues. last year i zapped my cluster jumping the car (doh!)
had that fixed last month and everything has been good....until last night
i came home from a 60 mile trip and parked it. i went to start it today and it fired up but the battery was weak. i noticed the right turn signal on the dash was on. i had to go to work, so i left it. i looked at it tonight and the battery was dead. i switched it out and not only is the indicator on, but the right side turn signals are on; not blinking but solid. i started the car and went looking for obvious answers.
yesterday the washer fluid light went on, so i was going to get some to fill it up, and i look back and the lights are out! great right?....not so fast. i shut her down and after 10 minutes i looked outside and they're on again!
anyone have this bizarre issues?
thanks
gregg

Gilly · #2 06-09-2011, 08:18 PM

Well I did reply on the SL forum.

One thing that was mentioned was the "curb side parking" on the light switch, again as long as the arrow on the knob is facing 12 o'clock, then this has nothing to do with your problem.

I have seen that style of ignition switch fail, which will cause some pretty odd problems.
When you catch it acting up again, try wiggling the key back and forth a little to see if the symptom stops. If it does you probably need a new ignition switch. I've had this specific problem (turn signal bulb coming on on one side of the car with the key off) on 129s and 140s, which use the same style ignition switch. Power will feed back from the ignition switch to the fuse box and to the turn signal switch. If you get this happening, it's easy to test by removing the appropriate turn signal fuse.
Other thing I've seen causing phantom problems like this are loose screws under the fuse box (the ones that hold the wires to the busses).

Gilly · #3 06-09-2011, 08:26 PM

Read your reply on the SL forum, correct the curb side parking position will not make the turn signal indicator on the dash come on.

The other potential problem I have listed (ignition switch) WILL.
PS by ignition switch I mean just the electrical portion. This is relatively easy to replace.

Hogweed · #4 06-09-2011, 10:55 PM

do tell...how easy is it?

Quote:

Originally Posted by Gilly

Read your reply on the SL forum, correct the curb side parking position will not make the turn signal indicator on the dash come on.

The other potential problem I have listed (ignition switch) WILL.
PS by ignition switch I mean just the electrical portion. This is relatively easy to replace.

Gilly · #5 06-09-2011, 11:14 PM

Remove knee bolster.
Disconnect battery.
Turn key to "ON" position. Leave in ON position until new switch is inserted.
Push square button in center of ignition switch electrical connector, which allows latch to be slid and connector to be disengaged from switch.
Push in on 2 plastic retainer pins which hold switch in to housing, slide switch out of lock housing.
Slide new switch in to housing, helping retainer pins to lock if neccesary (sometimes they click right in to place).
Reattach connector.
Done, well, except to test then reinstall bolster.

That pretty much covers it, the bolster R&R is the hardest part of the job (129s are easier in this regard than 140s), although first timers may get hung up on pushing in the retaining pins.
The real trick to keep in mind is to keep the switch in the ON position, it needs to be there to remove the connector, to remove the switch, to reinstall the switch, and to install the connector. Compared to previous switch and lock systems MB used, this is ridiculously easy.
Gilly

Gilly · #6 06-09-2011, 11:17 PM

But be sure to test that this is the problem. Easy enough way is when the light is on (with the key off), pull the fuse for that light, if it goes off, you found the problem.