Volvo: overdrive switch, soleniod, ok check

Question
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Followup To
Question -
I recently bought a 1986 240 DL with automatic trans.  It will not shift into overdive.  My overdrive switch does not work.  The indicator light stays on.  I can here the relay click.  I've been told there is a common problem with the wiring to the transmission.  What can I do to find the problem?
Answer -
The wires coming from the shifter down to the solenoid often flake off their insulation after a few years and start to short out.  To see if this is the case, pull off the shifter cover and look down around the transmission with a flashlight.  Also, from under the car, you can use a flashlight and feel up where the wires come down.  If they are stripped, replacing them with new wires will solve the problem.  Good luck!
Follow-up Question-
Ok, I replaced a section of deteriorated white wire that ran from the bottom of the shifter area to the side of the trans. Didn't work.  What's next to check?  The relay?  The solenoid?  The indicator light on the dash changes brightness and I hear a click in the area of the relay when I press the switch on the shifter.  What do you think?

Answer
You should probably get under the car and check the voltage going to the leads of the solenoid when you press the switch.  If you're hearing the click behind the dash when you engage, that means the relay is probably ok.  Check to make sure you're getting 12 volts down at the solenoid itself, and if you want to be thorough, check to see you get an output 12 volts from the relay when you press the switch as well.  If no voltage at the solenoid, there is some short or break between the relay and the solenoid, so you'll have to retrace.  If you do get a voltage, but the solenoid doesn't make a sound, you probably have a bad soleniod.  Those can be bought 3rd party and changed out in a few hours, so it's not a huge deal.  Good luck!