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1984 300sd turbo
18 Posts
Discussion Starter #1
I almost have my new-to-me 300sd ready for its safety inspection. The
last problem I have is that my right turn signal doesn't work. I have
checked the flasher and rebuilt the emergency switch. After rebuilding
the emergency flasher the left turn signal started working but the right
is still dead. The fuses, I think, are OK because all the emergency lights
flash and the left signal works.

This leads me to the combo switch on the column. Before ripping the
stearing wheel off to replace the combo switch, I thought I would check
the continuity of the switch at the connector where the combo switch
plugs in. I removed the under dash carpet and took a look under the dash.
At this point I thought I would ask for help. There's a lot of stuff under
there, and without a manual I don't want to monkey around and maybe
make things worse.

Can anyone offer any help to a newbie on where I should be looking?


1984 300sd turbo
18 Posts
Discussion Starter #2 (Edited)
Well with no help from anybody on this forum, I decided to press on :)

To remove the steering wheel I first tried a ratchet wrench with a 10mm
allen driver. No dice, couldn't get the steering wheel bolt to move. Next
I tried an impact wrench with 90psi of air behind it. Still no joy. Finally
I bought a 24" long 1/2" drive breaker bar. Using that and a piece of rebar
through the spokes of the steering wheel to hold the wheel the bolt came
out surprisingly easy :)

Before taking the steering wheel off the splined shaft I scratch marked the
spline and the wheel to make sure that I could put them back together
correctly. The wheel came off the splined shaft rather easily, and I was
looking at the combo switch. There are 3 brass screws holding it in. Two
of them are short and the other one at the top is longer. After removing
these screws the combo switch was loose enough to pull back. I could then
see where the 2 cables attached to the combo switch run down the
column and under the dash.

This is how I found the connectors I was asking about in the original post.

The connectors are just under the edge of the dash where only a
contortionist could ever see them. They are just back from the edge
of the dash where you have to reach around back towards yourself to
get them. The good news is that the connectors pull off very easily.
With them disconnected the combo switch pulls out of the steering
column very easily also.

I then tested the switch on the bench with an ohm meter and found,
as expected, that the right switch wasn't making contact. I tried
re-soldering all the connections with no luck. :-(

Well at this point I could either throw the switch away and buy another,
or I could try fixing it. The switch itself is held on to the combo switch
assembly with 4 brass rivets. I drilled out the rivets and lifted the turn
signal switch off. Inside I found huge brass contacts that were corroded
with black gunk. A little emery paper cleaned the contacts and some
new aluminum pop rivets put the assembly back together.

Put the combo switch back on the column, replaced the connectors
under the dash, and I have turn signals again. :)

In retrospect, I probably could have used a spray contact cleaner and
gotten the same results without drilling out the rivets.

So if anyone else finds themselves in a simular situation don't be
afraid to try this yourself. It wasn't that difficult of a job.


Premium Member
2012 CL550 4MATIC Coupe
9,992 Posts
Good job! Though when this happened to my combo switch, I replaced it. They are prone to failure. You may have to repeat this job in the future.

Good fix though. Some pics would have been helpful. Also, yes, the steering wheel nut is a bitch to get off. I use my 300Ft.Lb. impact driver to get the nut off, or a long breaker bar as you did.

1986/1990 W126
14,158 Posts
Well done. Yep that steering wheel bolt can be tight, its a bit awkward if you are on your own as you kind of need someone to hold the wheel.
The other day I took off one that looked to have been on there from new super tight. Nobody to hold the wheel but I managed to put one of my legs through the wheel to hold it while I levered on the bolt which worked a treat.
Then I smacked myself in the face when the bolt came free, lol.

1984 300sd turbo
18 Posts
Discussion Starter #5
Yeah the steering wheel bolt was a problem :)

A 250ft/lb impact wrench didn't phase it. Maybe I should have spent the
bucks for the 350lb one, but my air compressor isn't big enough for this.

The 24" breaker bar and the 4ft long piece of rebar through the steering
wheel spokes allowed me to use surprisingly little effort to get the bugger out.

I need to poke through the forum and see how to upload pictures. I know
how thrilled I am when I find other people have pictorials of their projects.
As they say a picture is worth a thousand words :)
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