Ignition Coils - Ewwwww

I told my Jag tech bud to spend a bit of time today looking over the hoses, belts, and wiring in the engine bay of Superblack carefully for signs of cracking, hardening, etc. Sure enough, he found a disaster maybe waiting to happen with the white wires right where they connect to the coils. The insulation appeared cracked and even a couple of spots of one of the wires was bare :grimacing: The tops of the coils themselves looked ancient, and even appeared to be starting to rust. :confounded:

So, I’ve ordered two new coils. As to the wiring, my tech seems to think we can wrap the bare spots with heat shrink wrap (like used over spliced connections) to get them safely insulated again, at least electrically. There doesn’t appear to be new connecting wiring available for same. :frowning_face: The only thing that worries me with using the heat shrink stuff is that area is (obviously) subjected to a lot of heat anyway, so wondering if that will cause the shrink stuff to distort over time and maybe even slip off. :thinking: Your thoughts on this, please …

A bit of good news, though … the major radiator and heater hoses, as well as the belts, appear to all be in good shape. One hose though that he found very hard was one (about 1"-1 1/4" diam.) leading from the radiator end of one of the valve covers to somewhere … Need to find out what that hose is for and get a new one, very soon.

Hi Paul,
Bad advice and so removed! (Edit) Thinking Lucas here.
There isn’t anything special about the existing coil wiring- why don’t you trace it back to where it is undamaged, and put in a new section of heat-resistant wiring and connectors. Then you avoid the “patches” and risk of embarrassment on the side of the road when you get a “short.”
Paying special attention to hoses is a good idea!

Heat shrink is fine for car engine temperatures. You can also get a
glued inner liner, it tends to make the wire a bit rigid.

Jim Brighton UK

I believe that Paul was posting about his 1992 XJ-S V12 with the Marelli ignition. AFAIK there is no simple replacement of the two Marelli coils with a single one as has been done in some of the Lucas ignition cars. Or did I get this wrong?


No, Paul, you are quite right. In my dotage I get confused between the “Supercars” and I would probably find it easier when the vehicle in question is identified by year and engine. My fault!

Thanks for explaining.
I believe that anyone asking for help with their car should provide the minimum necessary information about their car in their subject line or body of the post. I am regularly amazed with how few people actually do that. I guess I am getting grumpy in my old age because I now often ignore posts without the necessary information and just delete them, or reply that they didn’t provide the model year, engine, transmission or other necessary info for me to know if I can help. Sometimes I will jump in like I did on this string when I believe that someone replied with incorrect or misleading info because the original poster failed to include necessary info.


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Ah, I had wondered about that, as I didn’t remember ever reading anything about being able to combine two coils into one on our XJSes. Speaking of “confusion”, when I was looking at new coils on Ebay some of the vendors of them were apparently also confused, in regard to parts # and fitment. I saw some of the earlier version of the coils (i.e. Lucas) as being advertised “for Marelli ignition (cars) only”, and vice versa. :open_mouth: Good thing I carefully checked them out (and the Classic site) before I made my purchase. :relieved: I wondered what would have happened if I had bought and plugged Lucas coils into my Marelli system (assuming the connectors are the same)? :grimacing:

The Lucas CEI system used two coils wired together to provide a big enough spark, one was just a slave for the other. Modern coils are more efficient, and you can replace the twin coil set up in this instance with a single one. The Marelli system has one coil per bank and there is no way to replace them with a single coil. You would need to check the specs, but it may be possible to use a pair of Lucas coils, wired correctly for the Marelli set up.

On my 1992 XJR-S I have the Zytec system that uses a Lucas distributer, but with different internals. It originally came with a single coil, but it was not very reliable in service, and mine has been retro fitted with the older Lucas style, twin master/slave set up. Both coils are the same, the windings are paralleled together, only the coil in the V has an HT lead attached. At some point I will replace it with a modern, single coil set up.