Temperamental Tach!!!
 

Hi guys!
I have had 2 W123's now with the same problem... sometimes the tach works, sometimes it doesn't. Anyone know what I should look for? I really want to get this pesky little problem solved.... Thank you in advance, Sabina :)

Your amp is failing or loose on each one. Its a black cylinder located on the driver side fender near the glowplug relay.

Put a piece of cardboard under the tach amp cap to extend its life or repace it with one of Techguy's modern replacement amps and never worry about it again.

http://www.peachparts.com/shopforum/showthread.php?t=219949

Unless of course it's an 85, in which case a common problem is the EGR controller connector behind the passenger kickpanel (there is no tach amp on the 85s).

http://www.peachparts.com/shopforum/showthread.php?t=138818

"W123" covers lots of possibilities. Year and model would be much more helpful.

How do you get the cap off?
 

Mine wasn't working either. I bought a tail light lens on ebay and when I paid, the seller offered a new tach amp for another $25. What a stroke of luck. Works like a charm.

I'd like to check the old one out to have a spare.
When I take off the cover, the guts of the amp go with the cover. Looks like there is a molded ridge that holds it together. Do I just cut down the ridge to get it out and get to the place to add cardboard?

Grab it with a pair of pliers and pull hard.