I have an odd #1 plug wire on my 1975 450SL, that I need some help with. It has a sliding rubber thing on it with a wire coming out of it that goes to some sort of electrical socket by the power steering pump. It appears to be some sort of test site plug. Is it where a MB mechanic can plug in some sort of tester to check firing order and/or other componets on the car? As I need to replace #1 plug wire is that extra thing a necessary item (is it vital to car operation)?
Thanks for any help.

Can you post us a picture. I worked on many 450SL of that vintage but I dont remember this. I's also been 20 years.

John Roncallo

I have no experience with your model of MB but that said it Really sounds like a Diagnostic Test Lead. Most likely some fella with a dyno-tune had to buy a new lead. There is often a test lead put to the #1 when diagnostic's are done.

You could always put a replacement plug wire on and run it to see if something’s amiss! I wonder if there was an after market performance enhancement done on your car?

On my 450sl 1977 there is a female diagnostic plug mounted inside the drivers side fender. (in engine compartment) this mates with that "extra" wire. Used for diagnostic checks in the old days. Not used today methods. regards, Abe G

Sorry it has taken so long to get back. Thanks for the input. Here are some pictures if anyone is still interested. I haven't had a chance to try it with out this in line, as suggested, I will be able to this weekend.
Again, thanks for the help.
Doug

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Yep, Diagnostics. Coil it up and keep as original equipment. May make someone happy many moons down the road when you go to sell it!

Put new wire on without it.

Thanks so much for the info. My orginal thought was it was no longer needed, however I thought it best to check with the experts (the people who are on this site).
Doug