Lucas 33117D Flasher Relay

Hi
I have a 1958 XK150 that I am in the process of rewiring. The car has the single bulb flasher/brake taillights.
Can any one help me with the correct wiring sequence (negative earth) for the Lucas 22117D flasher relay unit? Any help greatly appreciated.
David.

I have a wiring diagram which i will dig out and post, if nobody else beats me to it.

Thanks Wardell - would be very helpfull.

XK150 has positive earth electrics, unless it’s been modified

Yes Roger, but I wish to modify it to negative earth.

David,

I did this drawing for someone else on the list last year. I think it has enough information for you to wire yours up correctly. The relay doesn’t care whether it is +ve or -ve ground but the case must be grounded for it to work.

Eric
Shropshire, UK

Eric

Thanks for the diagram, it’s exactly what I was looking for!

I too have a 58 XK 150 that I have rewired to negative ground. I used the XK’s wiring booklet for the 150 and found it very helpful. Other than the fact I installed an alternator instead of the generator, and needed to flip the wires on the voltmeter, it was a pretty straight forward procedure. I have also converted all the lights to LED so I am using a different flasher relay but the wiring is the same.
Len Wheeler

Thanks Len

I hadn’t picked up the need to swap over the contacts on the ammeter, so that’s a very useful piece of information.

And your clock won’t work if you convert to negative earth, albeit it will show correct time twice a day.

The coil wires also need changing over.

The clock that came with the XK150 will work with either battery polarity. If someone has modified it then it could be different. The modification that Jaguar did on the positive ground E-Types had the undesirable side effect of causing the clock to burn up if the polarity was reversed. My recommendation is to disconnect the clock if it doesn’t work, just to be safe. Later on you can send it to someone who knows how to fix it.

1 Like

Thanks Guys

It’s not just the wealth of knowledge and information out there, it’s the willingness to share it - great club, glad to be a member.

Thanks for correction Mike, should have asked you in first place. My first hand experience is with many Mark 2 clocks, when we went through a period in the 1970s/80s of converting Mark 2s to negative earth so we could fit the then newer sound systems only available in negative earth, and didn’t really care about clock not working. Presumably Mark 2 clock has similar modification as you say 3.8E types have. Can you quickly advise what the modification is?

Not that I have any intention of converting an XK to negative earth ever again, as there are better ways of fitting modern accessories now if desired, whilst still retaining original positive earth electrics. Indeed there appears to be a major down side now strongly suspected with negative earth converted XKs becoming more apparent, but little known nor understood- so I just can’t see the point, of taking any risks for zero benefit.

Presumably all XK clocks, and same age/earlier saloons, are similar, predating design change introduced with Mark 2 and 3.8 E type clocks, regarding this polarity change risk - unless compently modified.

Hi Roger,

The original clocks that Smiths made for the Jaguar product line have a simple circuit consisting of a switch in series with a coil. Every time the balance wheel passes its neutral position the switch closes momentarily, sending current through the coil to generate a magnetic field which gives the balance wheel a little nudge in the right direction, keeping it oscillating. The side effect of sending and interrupting current through a coil is the generation of high voltage, which is the way the ignition system works in your car. This voltage causes a spark every time the points open, and at 5 ticks per second that amounts to over 157 million sparks per year. Although the points were made of beryllium, they were only 15 thousanths of an inch wide and 7 thousanths thick. As you can imagine, it doesn’t take much erosion per tick to have a large effect after a few hundred million cycles.

In 1963 Smiths added a rectifier across the coil to suppress the arcing. Although this may have helped a little bit it did not solve the problem, and had the unfortunate side-effect of making the clock polarity sensitive. “Sensitive” is too benign a word. Reversing the polarity would cause the contact spring and the hairspring to become a puddle of molten metal. This was at a time when electronics were being increasingly used in cars and everyone else in the industry was using negative ground. To notify people of this problem they affixed a notice, printed in four languages, warning of the dire effects of reversing the polarity to the clock. Unfortunately the notice was affixed to the clock itself, where no one could possibly see it.

With the introduction of the alternator Jaguar switched to negative ground, and prominently added the words, “NEGATIVE (-) EARTH” to the face of the clock itself. This was obviously ineffective and too late, since it’s impossible to switch a negative ground alternator to positive ground, and no one ever wanted to do that anyway. I can only imagine that it was placed there to remind the driver that Jaguar had changed their polarity standard, and to hopefully keep him from connecting the battery with positive ground, since that would destroy the alternator which had no protection against that.

To be fair, from our modern perspective it is easy to feel superior to the designers of these cars, but we need to remember that back when the XK120 was made, tubes (valves) were the highest technology in electronic devices. Today I use a crystal controlled microprocessor that fits inside the clock case to influence the original clock mechanism to keep accurate time, and it will work equally well with either polarity. It’s amazing how far electronics has progressed within our lifetimes.

Mike Eck

New Jersey, USA

www.jaguarclock.com

'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2

Len-
What flasher relay are you using? What is the manufacturer and part number? I switch to LED’s and all my turn signals and they work fine but I’m not getting my indicator light to flash. I get a very dim glow with an incandescent and almost nothing with an LED light… Sure could use your help buddy!

Don’t forget that the fuel pump is generally polarity sensitive also