In <199606022311.UAA04808@ra.isisnet.com>, Williams/MG Guy wrote:
>Need to reconstruct the wiring harness for the overdrive unit. This is new
>territory for me, so I could use some guidance/wisdom.
The scheme varies depending on the year of production of both your car
and the OD tranny. I can't speak for the older systems that had a
vacuum switch etc on them.
There are essentially three elements in the OD circuit, (1) the user
switch, (2) the lockout switch and (3) the solenoid. Until '74 1/2 or
so, the user switch was built into the windscreen wiper switch. You
pull it towards you, it applies 12 v to the power lead (the yellow
stub on the passenger side of the firewall). The later cars had the
OD user switch in the shifter knob. I do not know what this scheme
was exactly, but somehow uninterrupted 12v had to be present at the
shifter knob.
>
>There appear to be three points for electric connection. One is a dual-pole
>switch on the left of the tranny, there's a smiliar one to the right, and a
>single-pole connector on the right hand side of the gear tower.
Strictly speaking, those aren't dual _pole_ switches, but they do
have two tabs on them. The one on the right side is the reverse light
switch. It closes when you put the tranny into reverse. One wire to
it (should be in your existing harness) is the 12 v supply, the other
wire (also existing) goes to the reverse lights. The one on the left
side is the lockout switch. This closes _only_ when you are in 3rd
and 4th gears, which prevents engaging the OD in lower gears or
reverse, which turns the itty bitty OD gears into crispy critters.
One terminal is connected to the user switch, the other to the
solenoid.
>
>I was able to salvage the remnants of what I believe was this
>harness. That old GT was originally equipped with OD, but whomever removed
>the engine, chose to chop this harness. What's left are two green wires, and
>a yellow/red.
Some of this is the reverse light stuff. You really should have a
wiring diagram for your car to figure out the color schemes.
>
>Where on the unit is the solenoid?
It is covered by a black or blue nameplate near the bottom of the
unit. There is a small hole beneath the plate. A free wire should be
dangling out of the hole -- that's the solenoid wire. If the wire
is not there, you will probably need some experienced help to see if
one can be attached to the solenoid windings. This is a very delicate
operation.
The connector near the shift tower may be attached to the user switch
in the shift knob, if you have one. Some trannies also have a
connector on the side of the tower casting that I have not figured
out....
The bottom line: You don't really need a harness, you need a single
wire (in addition to the existing reverse light harness on your car).
If you have a wiper switch user switch, the wire goes from the yellow
stub ont he firewall to one side of the lockout switch. Then you have
a wire going from the other side of the lockout switch to the
solenoid. The other end of the solenoid is grounded. That's it.
I can't give you all the details if your user switch is on the shifter
knob.
Notes: I'd put a 3-4 amp fuse in the line going to the solenoid.
Also, if you have not ever used the wiper switch OD switch, it will
probably not work due to corrosion on the contacts. Take the wiper
switch off the column and gently buff the contacts with some 600 grit
paper.
Good luck! A. B. Bonds
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