x26 connector, where are u?
 

Im trying to find x26 connector on my 1987 300D, but i cannot find it. Im tackling the job with the rpm guage not working, and i was following some guys thread about checking AC voltage at the diagnostic box, right at the battery (pin 2 - positive lead, ground - neg lead) I dint get anything, so im trying to find out if the wires are damaged from the x26 connector to diagnostic connector.

It should be under the fuse box, but there are only 2 connectors with only 2 or 1 wire coming in and going out (x26 had to have 12 wires). Please help...

http://imageshack.us/scaled/landing/...1027135922.jpg

Remove the tach adapter, pop the plug in out of the housing, install a quarter on top the silicon potting and snap back into place.

If the tach works, you have a bad tach amp, which is the #1 cause of an inoperative tachometer.

P.S. Takes less time that looking for X26 too...FWIW

The W124/OM603 doesn't have that kind of tach driver; the tach is driven by the EGR electronics (in the compartment behind the battery). The most common reason for tach failure in these cars is the OVP relay or the fuse in it (also located behind the battery).

Jeremy

Good catch, I missed that.

Guess I spend all my time working on the old ones!!!!!

You are correct, the 10amp fuse in the OVP can cause a lot of issues....Robert

I was about question Bert about that... thanks jeremy. I know its not the tach itself, because i switched from my e320 94' (e320 tach works) cluster to my 87', but it did not work, so it has to be wiring problem :/

Update: Fuse is intacted on OVP(5 pin), measured pins 31 (+) and 30 (-) *diode test on my voltmeter* and got 800, but if i do the opposite i get infinite. So I gave pin 15(+) or 31(-) 12v. Then i ohm/diode tested pins 30 and 87 to see if the switch closed, i got nothing. What do you guys think? Did i test it correctly?

Here is a diagram:
http://i870.photobucket.com/albums/a...g?t=1316966899

I think you did. Your first test showed that the Zener diode is probably good. Putting +12V on pin 15 and ground on pin 31 should cause the relay to pull in; if you don't get continuity between 30 and 87 then the relay may be bad. This is not the usual failure but it is possible. If the relay doesn't work then EGR won't and your tach signal can't get through.

You can try connecting pins 30 and 87 in the socket for a test; if the tach suddenly decides to work, the problem is definitely the relay. To do this test, start the engine and have someone watch the tach while you use a wire to connect for a few seconds pins 30 and 87.

Jeremy

you were right, connecting 30 to 87 pins helped. Tach all the way to the red (probably bad tach, still works) and rpm went up (~200 or so). Time to invest into new OVP :)

Thanks!

LOL as predicted (thanks jeremy!) tach works and increase of idle was noted... but the tach goes ALL the WAY to the red... seems like a defected tach. I'll try use a cluster from my e320 94', see if that has something to do with tach being broke or the signal (i hope its only the tach)

If the tach was from a different vehicle (I forget where you are in your parts swapping) it may not work properly in your diesel. I've never explored what the signals look like but gasoline and diesel models may be very different.

Jeremy

On 124s the gas and Diesel tachs are definitely different.

Gas tach in a Diesel pins at 7k as soon as you crank the engine.

Found this out the hard way.

My OVP internal relay went faulty, so I wired a normal silver 20A M.B. relay in its place and attached it to the case of the OVP...

The coil of the original relay was O/C

Saved trying to find one and the cost!

So im guessing I have to get a tach from a diesel w124 in order for it to work? Anyway to spot a diesel vs gas tach? no red rpm line?

I had the original cluster but the dome light mounting inside was burned beyond repair so my dad got used cluster from gas w124... plus he threw out the original cluster (big mistake) so i cant retro fit it into the new cluster that he bought -_-