Thanks for your suggestions.

I hooked the clocks up to my car battery directly and still nothing.

At this point I figured that I might have fried the capacitors, so I went back to the electronics store, bought four more capacitors (@ $0.16 each), and a low wattage soldering iron.

This time, I clipped a hemostat to the leads that I was soldering (To act as a heat sink), and soldered the connections as quickly as possible.

I am happy to report that BOTH clocks are now ticking and keeping excellent time.

Thanks again for your help.

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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 280K looking forward to 300K badge (or sticker??). >>You haven't really worked on a car until you draw blood<< :-}

You should have battery voltage at the clock - 12v. Here's a link that may help with the wire tracing. The small tach takes its power from the three prong plug on the back of the tach, so that would be a logical place to start.

http://www.davebarton.com/240tachinstall/

I'm suspicious of the 9.6v you see at the clock. If this figure is accurate, the clock probably won't run even if its electric components are healthy. You should test the clock with a known good power supply.

If the starter motor cranks, then there's certainly enough current to run the clock. Connect the clock directly to the battery, and see what happens. If the clock runs, then you have a wiring problem (high resistance) somewhere between the battery and the clock. If the clock doesn't run, then there's something awry inside the clock. Other than replacing the caps, which I've successfully done on several units, I have no suggestions.
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David Brick, Santa Cruz CA, 1988 245