The first and most important thing is that the wire from the solenoid
absolutely MUST go via a lockout switch on the gearbox in order to prevent
destroying the overdrive if the car is reversed and the manual switch is
still on. You will also probably get excessive torque reversals in first
and second which could cause damage. The lockout switch ensures that
overdrive is only operative in 3rd and 4th gears (4th only on late North
The overdrive was never fused from the factory, it comes off the unfused
ignition circuit. Adding a fuse is no bad thing particularly on the later
cars with the manual switch on the gear lever.
Since the gear lever switch is simply an on/off switch it will work exactly
the same either way round, and my Haynes doesn't show the colours to the
switch, only the colours for the remainder of the wiring.
My Haynes shows a white/brown going towards the gearbox switch which becomes
a yellow/purple en route which is powered (unfused) when the ignition is on.
>From the gearbox switch it should be as you describe. If you have the gear
lever switch and intend to use it you must use the yellow from the
gearbox/TCSA switch to feed the manual switch and not your stray blue or you
(or someone else) could wreck the o/d. It will be a good idea to insert an
in-line fuse somewhere in the white/brown or yellow wires between the
ignition and the manual switch.
If you propose to use the dash switch, then if you have TCSA and want to
keep that working as designed then you must still wire as above but up from
the gearbox switch to the dash switch then back down to the solenoid.
If you don't have TCSA then your dash switch should be fed from an ignition
feed, fused if you like, then go down to the gearbox switch and from there
to the solenoid.
Whichever way you wire it the feed to the solenoid MUST go via the gearbox
switch at some point.
----- Original Message -----
From: James Schulte <email@example.com>
Sent: Saturday, April 07, 2001 6:49 AM
Subject: Overdrive Harness Question
> On my 78B I have a LH Laycock black label overdrive 22/61972/ 073579
> It has one black wire coming from the driver side of the O/D up into the
> driver compartment to a switch on the dash. Another blue wire goes from
> the switch on the dash to a fuse on the left side of the steering column
> on the fire wall with 3 other post connections. My new wire harness
> that runs down the gear shift shaft has one brown and one blue wire.
> Which do I connect to the black(the brown?) and Blue to (Blue)? Do I
> run the blue wire under the carpet to the one fuse on the fire wall or
> is there some place else I should go? The Haynes book shows a Y (yellow)
> wire from the Transmission control spark advance micro-switch and a Y
> from the O/D gear/TCSA switch joining and connecting to a manual switch(
> I assume this is the switch on the gear shift knob) and then a YP
> (yellow purple) connecting to O/D solenoid from that manual switch. Any
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