Just recently bought a 1985 245 w/ a m46 trans. The overdrive has not functioned since I have owned it and I finally have some free time to try and diagnose the issue. For starters I can click the button on the shifter and hear the relay/solenoid clicking (also the "5" light on the dash lights up but doesn't stay lit). It does the same thing regardless if I'm in 1st or 4th which I assume is an issue lol.
Any ideas on where to start would be appreciated

 

I always start with the relay, I know it clicks but still... The lit up '5' in first is not right, so this is probably a wiring issue. After all the years, lots of opportunity for electric gremlins.

 

The 5 light on the dash lights flicks on then off regardless of the gear FWIW. And I'll probably go ahead and order a relay and see if anything changes

 

yeah, OD should be disabled in all but 4th gear. my next step would be to clip a test light to the wires to the OD solenoid thats at the overdrive unit, and see if that is getting power...

 

Would you happen to know if power to the solenoid should be momentary or always on when I push the button on the shifter?

 

i believe its powered to put it in OD and unpowered to take it out of OD. the OD relay thats behind the dash should act as a toggle. one press to go on, another press to go off, and only if you're in 4th. if you're in any other gear, it should revert to 'off'

 

So while I was waiting for relay to show up I drained the fluid out of the trans and od sump, also cleaned the strainer. Refilled with regular Type F as that appeared to be what was in it. Got the relay in this afternoon and all issues seemed to be fixed. No more "5" Light in 1st-3rd, and when I press the switch in 4th it actually goes in and stays in OD. Everything appears to work as it should. Thanks for the help with the diagnosing!