Marek- states on 6/2012 quote…
The gearbox top cover has a switch over the reverse gear selector
fork. This usually supplies the 12v (green) to the reverse lights
(green/brown).
Instead of this use it to supply 12v to the w1 winding of a 6RA
changeover relay. Connect w2 to earth.
Connect the same 12v from the w1 winding to c2.
Connect the green/brown wire to c1 so that the reverse lights come
on when the relay fires.
The c2 contact will have 12v on it any time reverse is not engaged.
Connect it to one side of your overdrive switch. Connect the other
side of the overdrive switch to the w1 winding of a 22RA relay and
earth w2 winding of the 22RA relay.
Take a NEW fused 12v supply with a wire capable of carrying 17amps
and connect to c2 of the 22RA. Connect c4 to the overdive solenoid.
The other end of the overdrive solenoid is earthed through its
casing.
The overdrive can thus only be activated if not in reverse gear and
automatically deactivates if reverse is selected as the 12v is
diverted to the reverse lights. If you want to limit overdrive to
top gear only, run the c4 wire through the second switch on the
gearbox top cover which is over the fourth gear selector fork.
If you don’t use a second relay (a high current 22RA) then you risk
burning out your wiring as the overdive solenoid itself can stick
open. It uses just 1 amp to stay open but a hefty 17 amps to fire,
fire being the operative word you will be wishing to avoid. The
second relay protects you from having to pulse 17 amps through the
overdrive switch itself.
Then in
reply to me on Thu 26 Feb 2015:
The main objective is not to engage the overdrive (’‘OD’’) when
reverse gear is selected.
The secondary objective is to have overdrive available from 4th to
make a 5th gear. If you look at the spread of gears on the 4speed
synchro box and the drop in gearing when OD is selected, depending
on box, you may find that engaging the overdrive simply replicates
the gears already present if it is used from second or third gears,
so it has no real practicality in these cases. The exception is
first gear, where OD creates and intermediate gear, so you can (at
your risk) play the traffic light grand prix and make a lightning
fast change up half a gear from just after the start. Using the 4th
gear switch stops such shenanigans.
To use the switches correctly and not strain the wiring loom, use
as follows with a 6RA changeover relay and a 22RA starter relay:-
Wire 12v to W1 of the 6RA changeover relay and take W2 to the
reverse light switch on the box. Connect the other side of the
reverse light switch to earth.
Wire the same 12v also to C2. C1 will be the reverse light feed
(green/brown) and this goes to the back of the car. C3 goes to
overdrive switch, which in my case is embedded in the gear lever
and the other side of the switch goes to W1 of the 22RA. W2 of the
22RA is earthed. C2 of the 22RA is a fused 12v feed capable of high
current and C1 will go down to the overdrive solenoid.
This arrangement keeps the high current feed away from the
overdrive switch as this is almost always part of a moving object
and wear and tear on the wiring as gear levers or indicator stalks
move will inwvitably lead to failure. The OD solenoid pulls 19amps
to engage and so this is kept well away from this weak link by the
22RA.
I have sketched both of these out …I just cannot make the connection how this works
Any help at all???