For a 1990 240 wagon (automatic) how do I determine if it's the relay that's at fault? I have no yellow up arrow on the dash lights (like I do on my 1993 240 std trans) and the button on the shifter does nothing when I'm at overdrive speed.
How do I trouble shoot this? thanks

 

What I did was simply pull it out and solder up the bad solder joints and put it back in. Since it's fairly easy to get at, this was an easy solution and it worked for me.

On the '90, you just need to take out the 5 (I think) screws that hold in the glove box to remove it. The relay should be on your left tucked behind the center console. Just remove it, pull the cover off and check the solder joints. Usually the ones holding the coil in it are the ones that crack and fail.

If the OD doesn't work after that, check the wire that runs to the soleniod on the transmission. This tends to fray and short out.

Good Luck

 

Resoldering worked to fix my OD relay also but I found another issue that the wire going from the shifter box under the car to the OD solonoid connector had deteriorated and was grounding out on the under body of the car when I hit a bump and would cause the OD to stop working till I turned the car off and restarted it. Once I taped up the wire with some 3M high temp electrical tape it now works perfectly fine.