Polarity issues

My winter project is to install air conditioning from retro-air on my 59 MK IX. In preparation, I am converting to negative ground with an alternator.

A few years back I purchased 2 new fuel pumps from XK’s unlimited (03-azx1318ep positive ground fuel pump) and one new distributor (Pertronix Flame-Thrower Distributor Jaguar Positive Ground - 17-D179600).

The fuel pumps and distributor were specifically for a positive ground car. Is there a way to reverse their polarity without buying new ones?

I’m already sinking big bucks for the air conditioning and alternator upgrade and am trying to avoid spending the extra $700.00 to replace the positive ground parts as was XK’s suggestion.



The only parts in your pumps and distributor that are polarity sensitive are the electronics, so 90% of what you have is just fine. You simply need to replace the electronic modules with ones with the correct polarity. I would be very surprised if Pertronix wouldn’t be able to provide you with the correct part to change the distributor over to negative ground. I don’t know the specific design of the fuel pump, but if it uses points then you could simply install one of Marek’s boards.

Let us all know how this conversion goes and what temperature you get from the vents.
Also curious about performance issue of the car and how it might affect the idle and how to keep the car running cool with the extra load.

This is coming from someone who was driven to Disney world and the grand canyon in the back of my MK2 from Colorado and it was HOT!! The car did not overheat and my father was a hero for attempting this feat back in the day when no one worked on Jaguars.



Will do! I figure my first step is just to get all of the polarity issues out-of-the-way, then I will switch to the alternator. I wanted to make sure that I do it one step at a time, so that if something suddenly stops working, it should reduce the number of steps to figure out where I went wrong!

Hi Joel, one way with the fuel pumps is to isolate the body from the frame altogether and run two wires: one from the body of the car (now negative to the pump terminal - also negative) and one from the fuel pump car circuit wire (now positive) to the body of the pump. I did this to a car radio at one point before I dismantled it and reversed the polarity internally. Just have to make sure you can’t short the car frame to the pump frame as they are different polarities. Can’t help with the Pertonix, sorry, Paul

Hi Gerard, I did a retrofit on the good lady wife’s XJ6 last year. I used a modern Sanden rotary compressor and other hot rod style kit (evaporator and condensor) - with great success. The evaporator is very compact and fits high up under the passenger dash - which is tighter than a MK2 in the XJ6. I would think that the limiting item in an Mk2 would be the condensor as the radiator in a Mk2 is much smaller than an XJ6. The 4.2l shrugs off the compressor load and I made no alteration to idle - it falls less than 50rpm when it switches in. Just a data point. Paul

Paul, which hot rod kit did you use? What kind of bracketry did you use for the compressor?


The thought of isolating the fuel pump hadn’t crossed my mind. I suppose if one isolated it well enough…

And you don’t forget, or the guy after you notices…

In your position I’d source just the electronics bits for the pumps (or find alocal ham who could convert the existing ones over).

And, like Mike suggests, ask pertronix about converting/returning your dizzy for a neg earth one.

If you do this I would also put an in line fuse in the circuit just in case it shorts out somehow. Also, are the lines to the pump body metal or of some non conducting material?

On an XJ6 they’re rubber pipe. Other models can be metallic - so that would be another change necessary - at least for the last little bit. Paul

I will send some pictures - adapted the original York XJ6 bracket. Paul

There are rubber hoses immediately after and before the fuel pumps. I will start the project on Monday.

Thanks everyone for your advice. It’s all converted to negative ground. A few things that I learned.

The fuel pumps XK’s unlimited sells as polarity sensitive are not. After I took them apart I realized there was no reason that I needed to make changes. The positive ground pumps that I bought work fine as negative ground.

The 502t radio has a polarity plug that just needs to be rewired. A simple 5 minutes with a soldering gun and it was done.

Next week I switch from a generator to alternator. See you soon!


someone has done an excellent pictorial of an aircon fitment in a MK9, the car is light blue, I have some pics, you may already be aware of it, if not, try google it

I found saved on my computer a 25 page .pdf with pics, entitled “alternator and aircon installation notes MKVII”, which I think is what I am refering above, I dont know if we can paste pdfs on here now, or i can email it if you wish

I am not aware of any pictorial work on the internet for the fitment of the MX IX air conditioning. I’ve looked quite a bit. What are you typing in to find this light blue MK IX? I would love any photos that you have for your project. My email address is JoelStobbe@hotmail.com.



I am not aware of any pictorial work on the internet for the fitment of the MX IX air conditioning. I’ve looked quite a bit. What are you typing in to find this light blue MK IX? I would love any photos that you have for your project. My email address is JoelStobbe@hotmail.com.



here it is (hopefully), using the Instructions on this site as a guide to upload a .pdf

If it doesnt work, let me know and I will email it

This is someone elses work, an excellent presentation, I think they would be happy to see it used by other Jag owners.

It is a mk7

edit…that did not work properly, dont know why, will email it

try this Joel, regards tony

alternator and AC installation notes mkvii.pdf (1.42 MB)

edit: I dont know why, but when I replied via email to you direct, this link popped up, and it DOES work!..I could not find the original searching Google, this is from my own Jag technical archive…sometimes things get taken down, links broken etc

It really is very handy, I do know someone with a MK9 who is also doing an A/C conversion, dont know how far he has progressed. I am retrofitting A/C to my 420G

Wow! That is fantastic! Thank you so much for sending that. That will make life much easier when the alternator arrives.