My Ignition Setup

Good Day,

I have a 53 XK120 DHC SE, up until recently it had the original '53 coil running with “standard” plug wires with the screw ends and a Pertronix Ignitor electronic ignition. I recently purchase a generic coil from Moss which has a plus and minus marked on the two secondary terminals. Before installation of this coil I would like to confirm which wires go the the positive an negative since the old coil was not marked as such.

Also consider the newer coil and the Pertronix is there a different type of plug wire I should be using?

any input is always much appreciated.


Just asking why we are changing the coil?
If your car is nagative ground? Black to minus
Red to plus on the coil
Are you sure you bought a coil without a ballast resistor?
Good luck

You should use non copper core wires (the originals) with any electronic ignition. Best to remove any ballast resistors if using a 3 ohm coil and pertronix. The original 120 had a resistor when used with points.

I’m with you 1,000 percent
But the Jag crowd has a fickle point and condenser following so I don’t wNt to start it again😀
IMHO in old posts new petronix i is are junk
Go 123 call in a day for life!
Wires and ngk plugs you are set for life

Answering only the original question, the old coil was marked SW and CB.
SW is to the ignition SWitch and CB is to the Contact Breakers.
If the car is still original positive ground, the wire on the positive + plus terminal goes to the contact breakers (the wire on the side of the distributor) and the negative - minus wire goes to the ignition switch (the wire going towards the firewall).

The original coil began to leak and was developing a miss when heat saturated. I purchased a coil from XKS and I have no idea if this part number has a ballast resistor or not. If this part is incorrect then do you have a suggestion?

As always thank you for the input,


Thanks for the input, what is your source for these parts if I can ask?

Thank you,


Looks like the new coil is from XK’s Unlimited, no ballast resistor in that coil so should be fine in an XK120. Should use plug wires with a non-copper core and no resistor in the plug caps. Pertronix are sensitive to leaving the ignition switch on and the engine not running for extended periods so be careful.

Thank you Graham,

I do still have the copper core plug wires with champion N5C plugs with the screw ends. I also have changed out the dynamo to an alternator.

I have been told and read so many opinions on the plug wires. I may be wrong, but it does not seem there are many option for non copper wire with the screw ends. From what I understand the coil, distributor cap and plug wire would all need swapped to push type. I am wrong here?

I was also told by a person at a jag parts dealer a person could run the the copper wire with resistor plugs using electronic ignition? That on the surface does not seem correct?

Do you know what the symptomatic problems are when running copper wires in this setup?

I have read so many threads about the XK running poorly when heat saturated, mine often exhibits this problem. My temp usually points straight down and at idle may get to 90. The frustrating part is question yourself is it fuel or ignition. Each step I have taken is making the issue better.

It seems at this point the next step would be to swap the screw in plug wire set with push in and get another coil with the push-in as well unless there is a solution of non copper wire with screw ends.


The copper wires will create resistance and send spikes back to the unit . It starts with A stumble at idle or driving then the unit just burns out.

Depends how “correct” you want it; I used the electronic ignition module and silicone leads from Powerspark Ignition in UK, I’m sure there are other local versions available wherever you are. I had to modify these to fit the original distributor, I used the spark plug ends as received and modified the other end to use them as a push on fit into the distributor and coil, works very well and the silicone boots really grip the towers tight.

I have to agree with Limongelli again… Pertonix is not reliable, especially the Ignitor II. I put the 123 distributor in my 120 OTS, at the same time a pal put Ignitor II in his Morgan. Friends and I did mine, while my pal took it to a very reputable shop. I took him to pick up his car and it broke down on the way home ! Back-firing, increasingly more violently, and eventually shut down. Traced the problem back to the distributor. The car is back in the shop and has been for 2 weeks.
I have heard from other mechanics who install many of them that they will NOT install an Ignitor II, but have had success with the Ignitor I.
I’m sure that XK-folks are going to start thinking that Limongelli & I own stock in 123Ignition !!

Wish I did !! Cheers & stay well, Knight


So far so good with my pertronix, I will need to do some research as to if the model is a I or II. The exhaust note is noticeably more throaty after having installed the pertronix, new wires to match, new coil and also recently swapped the generator for an alternator. I balanced the carbs and used the colour tune to help set the jets. She is running better than ever before.

Does 123 sell just the ignition module or does on have to buy the entire distributor?

I will certainly post back with any issue I have with it in the future with this setup.

Thank you,


James it’s a complete new distributor.
That’s what also helps with the uncertainty .
It’s when you open the cap though
There’s nothing there but a computer chip on a base
Again an old petronix were better then points but since the switch their actual product line has really fallen off quality wise

As Limongelli says, the 123 is the entire distributor only, and I have not heard of any problems from a whole-unit swap out where a new Pertonix distributor is installed. Stay well, k

Graham, yes that’s difficult, I was looking for a long ignition cable to fit in the engine nicely, bought 7 meters green wire plus resistance spark plugs , but did have a copper core so I just was back to fitting the points again and not electronic ignition, pity.
Maybe later I will change that to silicone and electronic.