My overdrive switch activatedit's self on my 1988 240DL. Where is the switch and/or solenoid located? Is there more than one item that may need to be replaced? Any special tools or trickes in replacing these parts?

thanks

 

The solenoid is on the left side of the tranny above the pan. The rubber cap on the solenoids goes bad and they lose contact. So far KAE is the most reliable replacement solenoid I've found.
The wire to the solenoid comes out of the bottom of the shifter above the driveshaft yoke. It often wears through and shorts out on the tailshaft housing of the tranny.
The relay is behind the center console left of the glovebox. Remove the glovebox and it will be on the left. Hella is the OE manufacturer of these relays.