Correct reverse light / cut off switch?

[Chris S]

Hi all - first post from me. I'm restoring a 1964 S3.8 auto, to a level to get it running and road-worthy again. Most work so far has been dropping the IRS to replace brakes and fix diff issues. However, this post is about electrics, specifically if anyone knows the right part for the reverse light/engine cut out switch, or can read the below and tell me why my logic is wrong...

The problem - my reverse lights don't work, and never had since I bought the car 3 months ago. The wiring and bulbs are fine, I know the issue is with the combined reverse light and engine cut-off switch located behind the steering column, because if I bypass it, the reverse lights come on. This switch is a 4 pin switch controlled by a rotating arm connected to the gear selected lever, and on my car it's a Lucas 55SA (photo attached).

So I bought a replacement, but it doesn't work either. When I tested them both, they have identical characteristics, ie my original one works the same as the new one. But although it fits and looks the same as the one in the Service Manual, I can't see how it can be the right part. Reason is the way the switch works - see 2nd image which represents the rotary arm of the switch and whether the switch is open (off) or closed (on).

IMG_1675.jpg (221.66 KiB) Viewed 2173 times

So both these Lucas 55SAs turn on the Reverse lights in both Park and Reverse, then off. And the Engine cut-off will disable the ignition in P, R, N and D2. So neither set of terminals does the right thing. A previous owner had connected the cut off wires to terminals 2&4, instead of 1&3, which would work, but then the reserving lights would come on at the wrong times, which I guess is why they were disconnected when I bought the car.

So do I have the wrong part, or am I doing something else wrong? Has anyone out there faced this issue or knows an answer?
Many thanks,
Chris.

[Chris S]

An additional thought - my switch would work if the auto gear order was P, N, D, L, R, which I think some Auto gearboxes did use. But mine is P, R, N, D2, D1, L. So I guess I need the right switch for that sequence... anyone can verify that and knows a part number? SNG Barratt can't help - "no longer manufactured". Thanks.

[cass3958]

Welcome to the forum.
Sorry can't help with the wiring as I have no experience with this. My car has the BW35 box where this switch is in the side of the gearbox where as you will have the DG250 with the switch behind the dash.

The part number is C22948 described as "Switch for reverse lamp and starter cut out". I have checked this part number with SNG and you are right it is no longer available. I have a contact who could have a second hand one but really you just need advise on the wiring side and I am sure someone will be along with not just the wiring diagram but photos of theirs wired up in due course.

[cass3958]

I have just read your post on the Jaguarforums.com and in that post you state this relates to the BW35 Auto box. Is this correct as your car being a 1964 should have the DG250 Auto box and the switch you are trying to rewire is fitted to the DG250 behind the dash. On the BW35 the reverse and cut off switch is located in the side of the gearbox. There is a panel in the left side of the gearbox tunnel to access it or you might have to go from under the car if your car has had a swap as the panel might not be there.
If you do have a BW35 box maybe the previous owner has swapped gearboxes, left the original switch in place but tried to rewire it to work with the BW35 switch.
Can you clarify which gearbox you have in the car please?

[Chris S]

Cass and all - I've just replied on the other forum but I'll do so here too in case some people prefer one or the other. (and apologies for double posting - I'm new to this and wasn't sure which forums are most active).

Thanks for the reply Cass. Good question - I'd just assumed it was a BW35. Now I've checked info on the dates when DG250s were installed, you're probably right since my car is either late 1964 or 1965. I've looked underneath and I can't seen anything stamped on the GB itself, but though I'm no expert the shape of the gearbox sump and convertor housing bottom cover both look identical to the DG250, not the 35, when I compared to the parts images on SNG Barratt's site. The original GB number is JBC22358P. (though of course someone might have switched boxes sometime in the last 50 years.) So let's say I have the DG250 gearbox since the dates match and the shape of external parts look correct.

However I've read that the P, R, N, D2, D1, L sequence comes with the BW35, and that's the sequence I have... but it explains why I'm being sent reverse light switches that would suit P N D L R if that's the norm for DG250.

So I'm still a bit confused but your question has helped me move forward, thank you. Any further thoughts greatly appreciated, especially re the right part or wiring for the reverse light.

Cheers,
Chris.

[cass3958]

Chris on the gear box there is a riveted plate that is situated high up on the left side of the main body. At least that is where it is on the BW35. I have no experience with the DG250 box so all the descriptions here relate to the BW35.
On the BW35 there is an inspection plate on the left side of the gearbox tunnel under the carpet. If there is no panel under the carpet you can look under the car at the side of the gearbox. There should be the gear change cable and a thinner second cable going to the engine bay. The second cable is the kickdown cable and attaches to the back of the carbs. There should also be some electrical cables for the inhibitor and reverse lights switch which is screwed in to the side of the gearbox just above the pivot for the gear change. If I am not mistaken there should be no electrical wires going to this point on the DG250 as these are all up behind the dash.
On My BW35 box there are two brass cooler pipes on the right side of the gearbox which run to the bottom of the radiator where there is a gearbox cooler in the bottom of the radiator,
On my car my gear change indicator is P R N D 2 1 on the dash. My car is a September 1967 built 3.4s Auto.
DG250 boxes had the prefix JBN or JBC and the BW35 began with FG.

Below are some photos of the side of my gearbox showing the inhibitor switch beside the selector and kickdown cable.

Inhibitor switch with Gear change and kickdown cables

DSCF8428.JPG (5.63 MiB) Viewed 2131 times

Below is the side of the gearbox showing where the I/D plate is situated but the inhibitor switch and gear selector cable are not attached but the kickdown cable is.

Side of gearbox showing I/D plate above inhibitor switch

IMG_0704 (3).JPG (333.45 KiB) Viewed 2131 times

[Chris S]

Very useful, thank you and confirms I don't have that gearbox. I think it's time for a non-standard solution - since I can't find the right switch to fit my car, I'll buy some sort of new microswitch and mount it where the current reverse light switch is. It should replicate the horribly mechanical original design perfectly!

Thanks again for your replies, very much appreciated.

[John Quilter]

You might try obtaining the correct switch from one of the used Jaguar parts suppliers, such as Jaguar Heaven, Stockton California or perhaps Welches in Stubenville, Ohio. Many of these old Lucas switches can be opened up, cleaned and made to work fine.

[RollyTG]

Chris - I am having the exact same issue with my 1965. I obtained a new switch from Vintage jaguar Parts and when it was wired up the problem persisted. In my case I haven't looked at the reversing lights, but the engine cranks no matter what position the switch is in. I am still trying to figure out if the switch was bypassed somehow by the previous owner because it didn't work. If I come up with anything I'll post about it. I am very much a wiring novice and my car club resources on the subject are out of contact for a while at least. I'll have a look at the light though and see if that clarifies anything.

[Chris S]

I never did find the right part, so I mounted a new micro switch to turn on the reverse lights when the gear stick was in the right place, and bypassed the engine cut off.

Perhaps not ideal, but it works.