Tach not working - Page 3 - PeachParts Mercedes-Benz Forum

edge · #31 06-25-2012, 01:25 PM

The part number is on the relay itself. You may be able to pick it up on ebay.

mach4 · #32 06-25-2012, 01:41 PM

Quote:

Originally Posted by Scottr

Thanks Yuke, this helps. I now know I have the correct relay. Your the first one to varify that my OVP relay was under the hood. I have voltage to the relay and I can feel it pull in the contacts when I push it into the socket. Sounds like its worth replacing just to make sure. I also checked the ohms on the pickup at the tranny per the post above. It shows 1.86k ohms. So I beleve that's correct also. The hunt continues.
Anyone k ow if these relays can be purchased at a local parts store? My nearest MB dealer is 365 miles away

I'll sell you the one shown in post #16 above. PM if interested.

Scottr · #33 06-25-2012, 02:54 PM

Just got the tach working, made a small jumper from # 30 to #87 in the relay plug. So even though the fuse is good the relay is not. The interesting thing is after doing that, I can plug the relay back in and I have the tach again. Any thoughts on this? Intermintant relay connection?

flainn · #34 06-25-2012, 03:28 PM

Quote:

Originally Posted by Scottr

Just got the tach working, made a small jumper from # 30 to #87 in the relay plug. So even though the fuse is good the relay is not. The interesting thing is after doing that, I can plug the relay back in and I have the tach again. Any thoughts on this? Intermintant relay connection?

Corrosion on the pins or in the socket. Use some electronic contact cleaner on the socket, and some fine-grit sandpaper or a pencil eraser on the pins.

mach4 · #35 06-25-2012, 04:36 PM

Quote:

Originally Posted by Scottr

Just got the tach working, made a small jumper from # 30 to #87 in the relay plug. So even though the fuse is good the relay is not. The interesting thing is after doing that, I can plug the relay back in and I have the tach again. Any thoughts on this? Intermintant relay connection?

Happens all the time. Even a small amount of corrosion on connectors can interrupt current flow, and often just unplugging and replugging is enough to restore the circuit. If there is visible corrosion, clean up the connectors and consider using some dielectric grease on the connection to help prevent this in the future.

edge · #36 06-25-2012, 04:42 PM

Quote:

Originally Posted by Scottr

Just got the tach working, made a small jumper from # 30 to #87 in the relay plug. So even though the fuse is good the relay is not. The interesting thing is after doing that, I can plug the relay back in and I have the tach again. Any thoughts on this? Intermintant relay connection?

How did you test and figure out what needed to be jumped?

Scottr · #37 06-26-2012, 09:26 AM

Guys. Before I posted my tach problem I hit the relay socket and relay pins with contact cleaner and a small brass brush. Thought I hit the basics before calling in all you experts

I must not have done as good of job as I thought.
Thanks again to everyone for all the help and insight.
EDGE. As far as the jumper. Iv installed a lot of relays in trucks and cars so I have a good understanding how they work, but, to make sure, as this is my first MB, with the key off I found one pin with 12v ( hot all the time) this handles the load. I also found one pin to ground, turn the key on and the third pin had 12v (this is pulling in the small coil inside the relay and making the switch from the " hot all the time pin to the last pin which is the load) so, I just jumped the hot all the time to the load and Bingo. If you search the web a little I'm sure you'll find a better example with pictures. I'm on my phone so I'm limited.
This might help, if your standing next to the drivers fender and you pull the relay the pins to jump are the two closest to the passenger fender.