1983 US 300D: Windshield wipers were working properly on all speeds today. I pulled the left side of my cluster halfway out to repair my dash light rheostat, and after reinstallation my windshield wipers no longer work on any speed. Fuse looked ok and the relay behind the cluster felt snug and untouched. What else could I troubleshoot?

The rheostat has to be pulled off the bottom area of the speedo, right?
So maybe while tugging you might have disturbed something.
Seems like the wiper motor relay is back in the general area. (?).

Also maybe its cold weather related.
That is, temporary.
It used to happen on my W126

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Yes, rheostat is right below the oil pressure gauge. Does the wiper motor relay control all speeds or just the intermittent speed?

If you completely killed the wipers then check the plug from the combination switch under the dash. If that is unplugged nothing will work. The wiper control pins are all in the teens and that is the cable end of the plug. If the cable got pulled accidentally then those would be the first pins to disengage.

The intermittent relay is behind the cluster on a 123 but if that is unplugged all you will lose is intermittent operation and the wipers won't park when turned off by the switch.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech