Correct reverse light / cut off switch?

[Treetrimmer]

Just a thought, but I was under the impression the description everyone is referring to as the "reverse light switch and ignition cut-off" isn't quite right. My understanding is that the steering column mounted switch does not cut-off the ignition, it inhibits the starter motor solenoid, unless the steering column selector is in "Neutral".
This may help understand the action of the switch.

Richard

[RollyTG]

Chris - could you post a picture of your setup maybe. Thanks

[RollyTG]

Thanks Richard - good point. Mine is still a mystery though.

[RollyTG]

Here's an update on my starter cut-off switch problem. It's complicated, which might be why it has taken me a goodly portion of the Covid year to get a handle on what is going on. I had put in a new cut-off switch at the same time as I installed a new turn signal switch back in about May last year. The new turn signal switch did not work, whereas the old one did - just the canceling mechanism was broken. And, with the new cut-out switch, the engine still cranked (and started - Yay!) but it did so no matter what position the transmission shift was in (not yay). And, with the engine now running, I was able to determine that the shift pattern is definitely not that of a DG250 which my car should have; it is the same as a Type 35 it seems. Apparently the transmission has been replaced at some point. This means that the cut-off switch was never going to work properly. In fact it would not work at all as the Type 35 transmission cut-out, as Cass has pointed out, is on the side of the box. So, with further exploration I discovered that to get around the cut-out switch mismatch, the whole cut-out mechanism wiring has been somewhat crudely, but effectively, by-passed. And that leads to the reason why the turn signals had ceased to work. It seems that there is a serious conflict (aka short circuit) between the by-pass wiring and the cut out switch which caused the fuse to immediately blow whenever the ignition is switched on. The turn signals are on the same circuit; so I disconnected the now superfluous (sort of) cut-off switch, the fuse no longer blows, and the turn signals now work as intended. The headlight flashed even works. That leaves me with a safety issue - the non functional cut-out mechanism - and a fairly inconsequential lack of functional reversing lights. Fixing that is a job for another day - or month. Now that I have the motor running and all the necessary lights working I hope to take the old girl for a short drive sometime soon to get a better idea of the how well the transmission and other bits work. This car has more tricks up its sleeve yet I am sure, but it sure is keeping my brain exercised. Any suggestions or advice on how to proceed from here would be most welcome.

[cass3958]

Rolly forgive me but I am slightly confused.

Which gearbox do you have in your car at the moment?

Your car according to the chassis number is a January 1965 car which should be fitted with a DG250 box as the BW35 was not used in the S Type until the end of 1967. I think that the method of selecting gears on the column ie P.R.N.D is the same on both gear boxes it is just the D has different settings in the display such as D.2.1 in the BW35 and D2.D1.L in the DG250 box. Now that you can actually start the car and drive it you will have to operate the lever and tell us which gears you select as the lever is moved. ie P.R.N.D. ?. ? or something else?

Being a 1965 car the cutout switch on your car should be under the dash and the selector lever should operate the switch. (as per your photo on page one) On the BW35 the switch is on the side of the gearbox and it is a lever inside the gearbox which operates the switch. There is then an additional wiring loom that goes from the BW35 switch to the ignition button to stop the car being started if in gear and a wire for power to the reversing lights when reverse is selected. This additional loom on the BW35 links to the original shorter wiring loom from under the dash where the DG250 cutout switch was.
According to the wiring diagram there is a white red wire from the starter button on the dash to terminal 3 on the cutout switch. There is a white blue wire from the starter solenoid on the bulkhead to terminal 1 on the cutout switch. A green/Brown wire from terminal 2 on the cutout switch direct to the reversing lights. There is a green wire on terminal 4 of the cutout switch which is the power live source and this is directly connected via the flasher unit as both are fed by the same power source. In the "S Type maintenance documents" at the top of the page there is a colour wiring diagram you can view. If you have the correct cutout switch wiring it up should be easy but not having a DG250 with the switch under the dash I cannot suggest the correct orientation of this switch and the lever on the back to get the gear selector lever to engage the correct terminals to get it to work.

[RollyTG]

Thanks Rob. It is indeed confusing. My shift is definitely P, R, N, D... whereas a DG250 should be P, N, D, L, R. Hence my conclusion that whatever it is I have, it is definitely not a DG250. To add to the confusion my transmission dip-stick is on the left side like on a DG250 and the torque converter appear to be the same as on the 250???? So far I have not been able to identify it because the exhaust pipes completely cover up the ID plate and even with my fibre optic camera I cannot see any identifiers. You gave me some tips previously on what to look for but until I can get it up on a lift I am not going to be able to check those out. I may have to remove the exhaust system to get at the switch (if it is indeed a Type 35) and to put in a new speedo cable. Another oddity of this car will make that more difficult than it need be - the exhaust is a very non-standard setup; being two one piece pipes each with one small cylindrical muffler box - all welded. As far as I can tell I will probably have to cut it up to get it off. Not looking forward to that at all. If only I had a lift this would be so much easier. Also my garage is pretty small but we have a plan to expand it. your wiring tips will be very useful down the way when I get to it. I am starting to get a better understanding of wiring at last. The old girl is testing me but it will all be worth it I'm sure. Thanks again.

[cass3958]

One of the main differences between the DG250 and the BW35 is that the DG250 had a cast iron body where as the BW35 was aluminium. Even without a ramp you should be able to check that out.
As for the read out on the gear selector Nacelle I am sure I have seen some DG250 cars with P.R.N.D1.D2.L as per the attached photo which is the same order as the BW35 P.R.N.D.2.1. I am sure someone with a DG250 and this setup can confirm or deny this.

Nacelle.jpg (216.27 KiB) Viewed 1258 times

Perhaps there were two configurations of the DG250 box and yours has been exchanged from an early box to a later box which is why the display does not correspond to the gears you are selecting. Just speculating here and I am sure Glyn has more details even though his car is a manual.

This a Nacelle I have got as a spare and must be what you have on your display but it not a BW35 display.

DSCF4100.JPG (5.48 MiB) Viewed 1257 times

This is the display in my BW35 car.

IMG_7420 (2).JPG (111.09 KiB) Viewed 1257 times

[John Quilter]

Well if it is in fact a BW35 with the switch on the side of the gearbox I would think this must be available from somewhere. Seems to me the BW35 was a common unit used on many Volvos, Triumph Stag, Austin/Morris Marina, MGC, Datsun 510, etc. Checking suppliers for those cars might turn one up assuming they are the same for different brands of cars but all had a starter inhibitor function and a reverse lamp function and as I recall all were P-R-N-D-2-1 shift pattern.

[cass3958]

Reading up a bit more this morning on the BW35 but can find no information on the DG250 other than it was a Borg Warner unit.

It appears there were three versions on the BW35 box. The first version the M35 had the P.R.N.D1.D2.L quadrant then in 1965 they introduced the M36 which had P.R.N.D.2.1 and had the facility to add an oil cooler which My car has via the bottom of the radiator. The BW35 was not used on the S Type until 1967.

Then in 1967 they brought out the M37 which had a higher torque rating and used the same quadrant as the M36.

Unfortunately I cannot find any information as to which box model was fitted to the Jaguar S Type under the guise of the BW35.

So my photos above show the quadrant for the DG250 box as P.N.D.L.R then the P.R.N.D1.D2.L refers to the BW35 model M35 box and finally the P.R.N.D.2.1. quadrant refers to the BW35 model M36 and M37 gearboxes which is the one I have in my car. I do not know if I have a 36 or 37 being late 1967 as there is nothing on the I/D plate to indicate either and mine has been changed out to a Daimler gearbox anyway prior to my purchase.

To complicate matters further the P.R.N.D1.D2.L quadrant was also used on the Jaguar 420 and this was fitted with the Borg Warner Model 8 gearbox so if you check under your car and find you have a cast iron gearbox casing with the P.R.N.D1.D2.L gear selection you might have the Model 8 from the 420 fitted as a replacement but this was never fitted to the S Type as standard as far as we can determine. Checking the I/D plate will confirm this.

[Glyn Ruck]

Rob, You & Orlando are the Auto specialists on this forum as fitted to S Types.

All I have is the BW Model 35 Manual. It is a better copy than this that I can send to your e mail if required. It's 21.3 MB so I cant upload it here.

http://www.kirks-auto.com/MGC/BW_35_manual.pdf