Volvo: 240DL Wagon transmission, relay switch, glove box

Question
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Followup To
Question -
A friend is having trouble with her '89 240DL Wagon.  It won't seem to shift into 4th.  She had the relay switch replaced...but problem still occurs.  Trying to avoid getting shafted at a dealer...any advise appreciated.
Answer -
Is the transmission automatic or manual?
Automatic - with overdrive

Answer
After replacing the switch, the next step is to look at the relay, just behind and to the left of the glove box.  Those are notorious for failure.  If that turns out to be good, then the next thing to check is the overdrive solenoid itself on the transmission, which can sometimes go out.  My money is on the relay, though, which shouldn't be to expensive to replace.  Good luck!