1985 300TD Tachometer (federal)

[dennislarock]

Hi... New member, new to Mercedes diesel, first post,

I have just spent about 16 hours (half the time on the internet) trying to get the tachometer to work.

What I've done:

Checked rpm sensor... receiving 5.67 volts at idle

Checked OVP relay... its receiving voltage and the fuse is good ...also, have 2 matching OVP relays from another 85 that definitely works in the other 85.

Checked EGR inside kickpanel... no voltage ...It has two wires going into it at the center pole and the pole directly above it. All other posts/poles are blank. The cap has the number 3 on it.

I read this from a 1999 and 2002 post: "the 85 has an electronic EGR control unit. The tach signal runs through it. There is a wire at the positive battery terminal that supplies power to the EGR" Is this true? If so, where is the wire... I looked at the battery and there is not a second wire attached to the + positive post. I then took the battery out and could not find any loose wires that would attach to it.

any ideas or is it time to tear into the dashboard?

Thanks... dazed and confused,

dennis