Just installed a new to me (used) tach/clock component of the instrument cluster in my 82 SD. The tach barely registers and the clock only works when the engine's running. The unit fit perfectly. I bought it from a forum member and have no reason to belive the tach/clock is faulty. It came from a 300SD of 80-84 vintage. The only obvious difference between the new and old unit is the new one has red zones on the tach face. The original unit's tach worked fine but the clock is kaput. Any guidance?

Thanks

Try checking the fuse for the clock. It's unlikely that the fuse is the problem but it's quick and easy to check. Sounds like you all time hot line isn't really hot all the time. Maybe the wire got hooked up wrong.

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You might want to check your ground. Jump a wire from the metal housing to the clump of brown wires (grounds) behind the cluster. There's a brass strap on the speedo that bridges between the gauges on the left & the tach/clock on the right to provide your ground.

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82 300SD 202K
82 300SD 233K
83 300TD 340K
82 300TD 98k euro (parts on the hoof)
85 300TD 282K
83 300TD 197K

Turns out that all clusters aren't 'drop in'. The tach/clock that I bought pulls a different milliamperage than the orig. Maybe this'll save somebody on the forum some $$.