Whining OD relay?

My wife's 1993 240 has had some trouble with the overdrive light coming
on. I took it out and resoldered the connections on the circuit board
that looked possibly cracked and for a few weeks it was fine. It has
just resumed this behavior again today.

Whenever the OD light is on, there is a whining noise coming from the
dashboard that sounds like it is in the vicinity of the relay.
Repairable (did I miss a cracked bit of solder?) or is it just time to
chuck it and buy a new one?

 

I've never seen one whine before, there's only about half a dozen
components on the board though so I'd try resoldering some more, if that
doesn't work you could replace the capacitors as that's about the only
other likely failure.

Do check the wiring to the OD solenoid though, if the insulation rots
out it'll short and burn out the relay.

 

Worth trying, I suppose. No cost but a few minutes of time.

When I soldered up the board and reinstalled, the OD solenoid could be
clearly heard to respond to the relay when pressing the switch. I don't
have any way to get under there and look at the wiring, so I'll have to
have that done elsewhere.

If the solenoid or the wiring is failing, would it produce the same
symptom of turning on the OD light? My wife's mechanic wanted to
replace both the solenoid and the relay (for several hundred dollars- I
find him to be overpriced and not infrequently wrong).

 

Bad solenoid or wiring won't turn the light on, but bad wiring can kill
a good relay.

I'm sure the solenoids can fail, but I've never seen it happen. I bet
80% of the (expensive) solenoids that get replaced are perfectly good.