Swapped in an AL117x today in the '85. I was lucky to find one on NY Eve (all the auto businesses closed at noon around here) and my wrench opened up his shop today just to do it for me.

On the way home I noticed my tach isn't working. Did he miss a connection or is something else wrong?

I am a happy camper, however. Seeing as I was in the beggars-can't-choose situation on the 31st, my parts supplier had to source from the most expensive supplier to get it that morning. When we opened the box (which is marked reman), inside was a spanking new alternator.

A welcome bonus, seeing as the last reman lasted under 24 months. A big thumbs down to Eagle Electric (big eBay seller of upgraded alternators).

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Might check your fuses. I had the same issue with my '82. There is also a tach sender on the drivers wheel well under the hood. Looks like a detergent bottle top. Sometimes those get a little touchy and like to stop working.

I would start with fuses first and make sure all the contact are clean and they are all intact.

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82 300TD
75 300D
99 F350 Crew Cab 7.3 Powerstroke

The '85 doesn't have a tach amp on the wheel well. It has a sensor on the engine intermediate plate and routes through the EGR controller. The EGR controller gets its power through the OVP relay which has a 10 amp fuse on the top. That's what I'd check first.

Here's the circuit



The OVP will look something like this

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thanks for the info. I did some reading on the OVP and will have a look when the ambient temps around here are a little more reasonable (I work outside).

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

I agree with Mach 4. The 1985 version of the venerable W123 had a number of changes that carried over to the W124 models and one was the new electronics mentioned by Mach4. (Some of these new circuits may have originated with the W201 model; you can tell by the first three digits in the part number.)

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

well, since the 201 debuted in 83 with the 84 model, I'm guessing that they just incorporated the changes to the last of the 123's...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!