I have a 1990 volvo turbo with 206,000 miles driven. My overdrive stopped awhile back and I have never had it addressed. My question is the following, since whenever I shift gears the click is heard and just wondering could the switch be shot. It has automatic tranny.

maybe?
more details would make this question more answerable.
There are 2 things that commonly go wrong with the overdrive:
-the relay's solder cracks or the relay dies - simply fix with a cheapo soldering iron.
-the solenoid dies and has to be replaced or byassed. there's a special kit from ipd, maybe from fcpgroton too.

abnormally, the switch in the gearshift will die, or there may be an issue with really old tranny fluid or somesuch gumming everything up. In my frankencar, the wire to the solenoid came loose and rubbed apart on the driveshaft.

So, does the light go on an off with the switch? does the light ever show? does the car just never shift? what?
If the light goes on and off with the switch, the relay is probably working, and the wiring probably intact, in which case I would say it's an intra-tranny problem.
If the light stays on, check the wiring. The FAQ says where the OD relay is. It's rectangular or square I think

good luck
-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond

In answer to this problem Ώ]the light goes on when switch is depressed ΐ]the relay has been replaced Α]the overdrive hasn't engaged in ten years. I have never changed the kickdown cable so apart from this as the culprit the only remaining problem could be inner tranny? Supposedly these are die hard aren't they??

The overdrive is basically a one-speed automatic transmission bolted up the rear of the gearbox.

The overdrive is actuated hydraulically by a piston in the solenoid that opens and closes to control the pressure of the transmission fluid. When the piston is closed, most of the fluid is recirculated through a reservoir to maintain just enough pressure inside of the overdrive so that the moving parts are lubricated. When the piston opens, the fluid is allowed to flow through a relief hole into the overdrive unit which increases the fluid pressure against a set of small pistons inside of the O/D box that push on the springs holding the conical clutch. When there is no pressure on the springs (actuating piston in the solenoid is closed), the conical clutch is fixed to the annulus which gives you a 1:1 gear ratio. When the actuating piston opens, the pressure on the springs engages a brake ring to stop the sun wheel and viola....the annulus is now turning faster than the cone clutch. How much faster is a function of the planetary gear running on the sun wheel.

So, if you are sure that the problem is not electrical (check the wire feeding the solenoid), then you have a leak due to bad seals or the piston has collected metal shavings and can't move a full stroke. Either way you'd have to dig into the transmission as the overdrive is in the same enclosure/body as the gearbox on an automatic car.