So you've noticed that Volvo didn't put any extra wire into their harnesses!

Try this - remove the passenger side center console panel, pull back the carpeting a bit, and locate the connector that has a Brown and a Blue coming from under the carpet into it and a Black and a Blue exiting its other end and going up to the dash (they go to the OD relay). Then push down the rubber boot around your shift lever to expose the black plastic sheath containing the (Brown & Blue) wires going inside the hollow shifter up to the knob switch. Feed a little slack into the wires going under the carpet at the connector while you pull that slack toward the shift lever and push a few mm into the lever tube. With a pair of needle-nose pliers, gently pull the little spade connectors in the shift lever upward that few mm. Repeat until you have those spades protruding enough to replace the knob and still be able to grip them with the pliers while you reinsert the switch contacts. You can "squeeze" the connectors a little with pliers to tighten their grip on the terminals before you insert them. Press the switch down into the knob and re-cap it so that it is actually compressing the wires a little.

After reassembling the knob, run the shifter through all gears and watch the still-exposed connector down by the console...if it moves around, you need to try to feed a bit more slack into the wires until it doesn't. Otherwise you are "sawing" the wires back and forth on the edge of the hole in the trans tunnel and they'll wear through, and short out or break, again leaving you with no OD. This should keep them in place there for a few thousand or so shifts.
--
Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and numerous old motorcycles)