A few weeks ago, the O/D would not turn on. I had stopped to wash the car, got in and started and the light was on. Assumed I had hit the switch (poor placement by Volvo if you ask me). But it would not turn back on, so I ended up driving it like that, and it eventually came on during a stop that day. I did my Brickboard research, and it did not happen again until today.
I remembered the fuse, so at the next light, I reached down and removed the fuse cover and saw that it was fuse 11. As I got up to speed again, I counted down the fuses as I touched them, and turned #11. The light immediately went out, and I shifted into O/D.
Always check the simple stuff!
I'm not sure if this is related, but both times I had stopped while the rear defroster was on. Is this a relay to the rear defroster that could be the actual culprit?
Anyway, I'm not sure what other repairs you can do "on the fly", but it makes me think up some funny scenarios.

Funny you should post this. I had the car completely quit few years ago. As I coasted to a stop light I thought that it could be the fuel pump fuse. I pulled the cover off and found which furse it was, pulled out the old and put in a new one in time for the light. Thjis week I was driving to Denver airport when my heater fan stoped. Again I found out which fuse it was and just touched it and the heater came back on. It reminds me of the movie "Never Cry Wolf" where the bush pilot climbs out of the cockpit to fix a fuel line on the wing.

Sounds like bad conductivity at the fuse tips and the holder contacts. Spinning the fuse in holder often solves it, at least for a time.

Yup, the rear defroster is on the same fuse. It draws a lot of current so my guess is with bad contacts, there wasn't enough current available to activate the OD solenoid.

My recommend - replace all gray/white metal fuses with the brass or copper ones. They don't corrode nearly as badly. I harvest them at junkyards. Or I believe you can get them at fcpgroton.com, but you'll likely have to call and ask for them. Once a year or so go over the fuse tips with emery cloth and the holder contacts with a wire brush or pen knife blade for a scraper (in the small holes in holder tabs). Remove battery ground before attacking the fuse holder contacts.
--
Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.