I have searched high and low through many archives for a finite design of a wiring diagram for operating overdrive in 4th only; disengaging overdrive in the event of reverse gear selection.
There are many descriptions, but I get lost in the mental trail (mechanical not electrical engineer!)
I understand a relay is required, but would greatly appreciate a simple wiring diagram which details the connections between:
Since you have not received a reply and since (so far as I know) OD was not offered on the E-Type… here are a couple of diagrams for a Triumph with an A-Type overdrive:
54 is the relay
N is 12V always hot
W is 12V ignition switched
56 is the overdrive switch
57s are the switches on the gearbox (1 for the 3-4 rod, 1 for 2nd gear)
55 is the solenoid on the overdrive
Not sure how that compares to what you will do though you will have only one cut-in switch that grounds when 4th is selected.
In this set-up there is no reverse lock-out - it simply does operate unless 2, 3 or 4 is selected.
Here is a second version which shows just one gearbox switch (like what you describe):
I added a slo-blow fuse on the feed to the OD solenoid to protect it in case the pull-in coil should stick on (should be a momentary 22 amps or so but will fry the solenoid if it doesn’t immediately release).
I also added a (snubber) diode off of C2 on the relay to get longer relay life.
Finally, I added an indicator light to aid night driving.
A creative sort could probably add a reverse lock out since there is already a switch with 12V operating when reverse is selected (TRs of that era did not have reverse lamps).
Hope this helps or at least provides a starting point.
Assuming you’re working on an E-Type which never came with OD, I don’t think you’re going to find a way to limit engagement to 4th gear only. It should be relatively simple to incorporate a relay so that the reverse light switch will prevent OD engagement in reverse, but otherwise it would work in all forward gears. Perhaps studying a Mk II wiring diagram with OD would help.
Theres some good info there thank you and the diagram well labelled. I know some have achieved interruption of rev is selected (as a mitigation for 4th gear switch remaining engaged - stuck)
The diagram is for a generator car - control box being the correct name for what is often called a voltge regulator (an old 2-bobbin electromechanical gadget).
You would use anything on the brown wire circuit (12V, unfused, always hot – possibly the line side of the horn fuse).
As I said in my first post…I am no electrician so a clearly labelled diagram is what I require. There is no relay in this set up. I guess A is rev and F is 4th gear selector sw? Where is the relay and how does it connect? I am as confused as ever. Is there a key for all the parts?
Hi Philip…the info Andrew posted above is as simple as it gets…if you dont understand it then really you need help from an auto electrician or friendy mechanic who knows electrics…your overdrive and gearbox came i assume from an xj6, S type or similar Jag…wireing details and overdrive operation is included in their service manuals as per the MK2 info above…they would have used very similar wireing to what Andrew posted above. …relays were not used in the circuit…but could be added if you want… A & F are the top gear and reverse switch…E & B are fuses D is your overdrive solonoid…all quite simple…you could extras to the circuit like a relay and a lamp to show when o/d is selected…Steve
Every Jaguar gearbox has two fittings on the top cover: one for the reverse light switch and one for the 4th (top) gear switch that feeds the power to the overdrive solenoid.
It’s a good idea to use one, as forgetting the O/D on and using reverse is a quick way to rebuilding the O/D.
Jaguar did it this way for every car they ever offered with an overdrive.
I had one in my Ser 1 2+2 and I was happy with it for 16 years and 67.000kms and I have a factory fitted one in my 1975 XJ6C.
On the E-type, if the car was automatic, the easiest way to wire it is to use the inhibitor switch and relay from the automatic.
The inhibitor switch, the reverse lamp switch and overdrive switch are all the one and the same part, easily available.
If the car was originally manual you need to get one more switch and relay and figure out where to mount them.
If the car was originally automatic, it’s easy, you already have the switch and the relay and most of the wiring. Just take the inhibitor switch off the auto box and put it on the 4th gear sttiker hole on the gearbox top cover.
In my ex car I wired a Lucas flip switch I put next to the shifter console on the left (LHD, if your car is RHD put it in the driver’s side) so it had a positive 12V feed coming from one of the fuses that are powered only when the ignition is on. That switch would then feed the power to the ex inhibitor switch, now on 4th gear. If that switch was on (4th gear engaged) it would feed via original wiring the ex inhibitor relay, found under the dash on the RH side, now the only missing piece of the puzzle would be to connect the wire that would enable starting in the automatic so it allowed starting whenever the starter button is pushed (like every manual car) AND to make a new wire from that ex inhibitir relay that leads directly to the solenoid feed wire on the overdrive. It gets the earth connection from the gearbox/engine.
Thanks Andrew. I found that wiring diagram very helpful. After testing, it turns out that all my switches are working perfectly. The issue must therefore be at the solenoid or O/D unit. Unfortunately I just got a new Bell exhaust system installed and can’t reach the solenoid. Will I have enough room to reach if I disconnect the down-pipe from the exhaust manifold?
Ground via engine - power from reverse light fuse. The switch is in the gear lever and the cable not pulled through for now. One of the reverse spades has two cables attached, so I guess OD is only locked out by the 4th gear switch and has nothing to do with the reverse switch.
If required Jack’s relay switched by the reverse light switch would make it work for other gears but reverse.
I wanted the override to positively disengage if reverse is selected. If for some reason reverse is selected with overdrive engaged (sticky microswitch or wiring fault)…its the end of the overdrive gears. Just employing some risk analysis and mitigation.
Hi Terry, I expect that if your exhaust follows the original pattern you would be dropping the long intermediate pipe - between the down pipe and those that go over the rear axle. You might also have to prop the gearbox/overdrive and remove the cross member (under the overdrive) to service the overdrive. Paul (Andrew has lots of other cars but not an XJ6).
Paul
I agree. Pity that I didn’t sort this out before the new Bell exhaust went it. The muffler shop added a few tack welds to the pipe-in-pipe fit of the individual sections. That’s one disadvantage to the donut w/clamp fitting of the original down-pipe. Thanks.
Terry
Hello, what car has the O/D switch in the shift lever. I have added a compact Cat A overdrive to my Jag 2+2 and would love to have the same type setup. If I follow your description it would be like a Triumph Spitfire with a engage/disengage right it the shift lever knob?
