1989 240DL. The speedometer & odometer flicker on and off together while driving without any apparent pattern. When the speedo works for a few minutes, it sometimes shows correct speed, sometimes some fraction of the correct speed. The cluster "service" warning light flicks on for a second along with the speedo/odometer. Everything else on the cluster seems to function normally (except for the bulb-out warning light, but I believe that is a different issue). Switching the windshield wiper lever to any position appears to trigger a change in the speedo/odometer connection, either off to on or on to off. Wired connections to the speedo on the back of the cluster have all been checked, cleaned, and tightened up. The connections on the speed sensor at the rear differential appear good, but I haven't tested the sensor itself. I suspect, with the service light also flashing and the effect of the wipers, that the problem is in the cluster.

Hoping that someone out there with some electrical savvy and/or experience with these speedos can point me in the right direction. Thanks!

 

speedo problems are usually *just* the speedo. if the whole panel is doing funky stuff, I'd be looking at the power and ground connections.

if running the wipers messes with other stuff, I'd *definitely* be looking at the dashboard grounds. I think on a 240 the dashboard controls and stuff are grounded on both sides of the transmission hump. 7/9's are grounded near the lower front door hinges, one side is the computers and signal stuff, the other side is all the power stuff.

just sayin'

 

Agreed that it sounds like a ground issue, but I've inspected and cleaned every ground point I can find. According to the manual, the wipers and speedo both ground to the trans hump just to the left and below the shifter on the driver's side. Seems like the most likely culprit, but I've checked, cleaned, sanded, greased that ground three times and all the wires leading out are in great shape. Can't find any signs of connection troubles under the dash. Rechecked, tightened up, greased all the connections to the back of the cluster. Today I went over the battery and other engine compartment grounds and made sure they were good. Checked the fuse box leads.

Still exhibiting the exact same symptoms: intermittent speedo/odo, flash of service light (but not other dash lights) when the speedo flicks on, and moving the wiper lever to any position makes the service light flash and the speedo jump on or off.

 

Found it: Loose ground in the steering column, just behind the wiper lever.