gauges jump when i honk the horn

[sshanky]

Hey all,

on my 1980 300SD and my 1981 300D, both of which have the same left-hand instrument item (with temp, oil pressure and fuel gauges), the gauges sometimes jump a little higher than they should be, but if I give the dashboard a few knocks they jump back down (and up again, if i keep hitting it). Sometimes tapping the horn causes the gauges to do their little jump up or down, other times it doesn't do anything. I notice that when the temperature and fuel gauges are lower, the effect is more pronounced. Any thoughts on what would cause this? Anyone else experience it?

Thanks

[koan]

Almost certainly a poor earth (ground) connection somewhere, my bet would be the multi-pin connector on the back of the cluster. Just giving the connector a wriggle or unplugging and plugging it in a few might fix it. Access is a bit difficult, reaching up from underneath requires some contortions but avoids pulling the cluster out.

koan

[sshanky]

I've had the cluster out and have rebuilt the whole thing (originally it was full of black oil, and filthy, and the odo didn't work, but it's all like new now). On the 300D the PO had attached a ground line to the frame and screwed it onto the board somehow. I always make sure it's attached...the 300D doesn't have such a ground wire though.