whats this thing ? ( XJ12 V12 ) Any 5.3 HE experts here?

[a8hex]

Looks like a condenser

[Jaguar steve]

It is indeed

[lowdrag]

I reckon it's a radio suppressor and should connect to the plus side of the coil to minimise interference. Does the radio "buzz", especially changing with revs? If so that'll cure it.

[a8hex]

I had a quick look in the Haynes manual and couldn't see a condenser mentioned in the ignition system.

Lowdrag is probably right. Someone has probably added it at some point to improve the radio reception.

[Jaguar steve]

Condensors are fitted to conventional points and coil ignition systems to absorb surplus electricial energy fed back from the primary winding on the coil when the points open, otherwise the points would arc and rapidly burn out.

A radio supressor is more or less the same thing - they're both capacitors - but it's purpose is to stop RF interference, usually heard because there's a poor earth or broken connection somewhere on the aerial or it's lead. They are fitted to the +ve side of a component - typically a motor or the coil - and earthed through the body of the supressor.

[a8hex]

JS, when I looked in the Haynes manual I couldn't see a condenser in the distributor, which is where I'd normally expect to see them, but then I'm not sure I've ever looked in the disti of a Jag V12, in fact I've not looked in very many distis in the last 25 years or so years. Perhaps a PO had decided that their should be a condenser and added one outside the disti since there wasn't a space inside for it. Mind you with a disti for a V12 you wouldn't expect to be short of space, there's probably enough room in there for a couple of extra seats.

[lowdrag]

If you do look inside a V12 distributor there certainly ain't room for a condensor! I still stick with my original thoughts on the matter.

[Jaguar steve]

No I wouldn't expect to see a condenser inside the V12 distributor because, if I recall, even on the earliest versions, it was never fitted with a conventional points ignition system.

So I'd guess it's been fitted at some stage to reduce radio interference. I often used to find this had been done as it's an quick, easy fix which usually works, rather than spending hours trying to locate the cause of the problem.

Confusingly Condensors / Supressors / Capacitors are the are same type of component, and look identical in many cases, but have different names and functions.

[Tame Technician]

It connects to the bottom of the workshop bin, then try to forget about it.

[Mike Hawthorn]

As I remember my 1985 V12 had a suppresser fitted to the Alternator which looked just like your one. The radio reception was not great so I changed it (the wire was broken) and in true big cat style it made no difference at all.