[TR] Overdrive Quirk

[Randall]

Are you sure it is the relay chattering, and not the OD solenoid itself?

If it is the relay, I would suspect that one of the isolator switches is not
properly adjusted or perhaps is coming loose.  Could also be a loose wire
almost anywhere, of course.

The OD solenoid delivers a very strong kick when the relay opens, which I
believe is what causes the Radio Shack relays to fail.  Adding a diode
across the solenoid (but mounted at the relay) seemed to work very well for
me.  The diode is wired from the output terminal (the one that gets wired to
the solenoid) to ground, and oriented so no current flows normally.  Any
power diode rated for at least 1 amp and 50 volts should work fine (I think
I used one rated for 200 volts).  Eg,
http://goo.gl/7OV4E

I can't prove that is the right explanation (or solution), but I've been
using the same cheap relay for over 10 years now after killing both a cheap
relay and a reproduction relay in a matter of weeks before installing the
diode.  Here's a shot of the cheap relay with diode (taken on my TR3A before
it got wrecked).
http://goo.gl/HDHjb

The wiring to the gearbox got replaced some time ago, but I'm still using
the same relay & diode on my TR3 today.

-- Randall