[Healeys] Overdrive Relay

[Simon Lachlan]

The other day my overdrive stopped working. (For the nth time. Toyota 5
speed please Santa).
Anyhow, it failed what I called the "click test" so I was 99% sure that the
fault was electric. First off, it's fused so the wiring was unlikely to be
fried and the fuse had not blown The relay passed its bench test and the
throttle switch was OK. So, I was pretty sure it was the solenoid...maybe
the gearstick switch but didn't seem likely.
So, I dismantled down to the solenoid. Not too serious in a BT7 and much
helped by having tunnel cover held down by stainless steel screws into
rivnuts.
Put a test lamp in lieu of the solenoid. Lamp lit up when OD was "On" and
stick was to the right. So, the problem WAS in the solenoid and final proof
was its replacement by a spare which solved the problem.
I took the rubber cover off the top and there was no evidence of frying etc.
All looked good. The solenoid was dead as a dodo..putting it across a spare
12v battery didn't induce a sound or a twitch.
Now, the question(s)..are there dud ones out there? Why/how did it fail? 
Just curious...
Simon
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