At first, it just quit working. Then when I got back in it to leave work, it would engage, but I could not disengage it with the button. Coming out of 4th gear is all that would disengage it, then I couldn't get it back on again. The next time was after it had been sitting again, fresh start-up, works fine a couple of times, then won't disengage with button, will disengage when shifted from 4th.

I read some posts about how to test the relay, but I figured OD Guru or someone else would be able to pinpoint the problem and tell me if the relay is causing this. Thanks!
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Kenny H Three SUVs, two cars and seven motorcycles

Check the wires from the shifter switch to the relay. Most likely causes in my experience are: wires pulled loose from the contacts on the switch itself, wires chafed through/broken under the rubber shifter boot.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD; hobbycar 77 MGB, and a few old motorcycles)

Thanks for that info, and I think you're right after driving it again today. It wouldn't work unless I pushed the shifter to the left and forward. And after I drove it a while, I had to lift off the throttle a little to allow it to just barely start to come out of gear to get the OD to engage, then put it back in fourth position.

Can I access all that stuff from inside the car? I'll do a search here and find out more info. Thanks again!
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Kenny H Three SUVs, two cars and seven motorcycles

If moving the shift lever affects OD operation it could also mean the problem may be the 4th gear switch.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD; hobbycar 77 MGB, and a few old motorcycles)

I took the advice here and looked under the shift boot. Found a bad connection at a previous repair with a crimped butt-connector. I soldered in a new wire to fix it. Works great now! I turned 300K last week and will be contacting Volvo for my 300K badge.
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Kenny H Three SUVs, two cars and seven motorcycles