Polarity switch and Mirrors

OK guys I am sure this has been covered before but I want out throw a twist regarding the conversion and whilst I am damn clever (geez he’s bragging) I don’t know everything.

I sent this to Ken Jenkins of the JEC in the UK.

"Hi Ken

I am sure you have answered this question a million times so I will give you as information as to what I have done so you can answer the questions.

I am converting my 1964 Jaguar MKII from Pos to Neg, I have done

New Neg Fuel Pump

New Neg Alternator

New Neg Clock (Electronic)

New Neg Dist.

Bypassed Voltage Reg.

New Neg Radio

Lovely Optima battery


What else,

Fuel gauge and or fuel sender unit wiring

Ammeter (do not wish to replace with voltmeter)

Oil pressure sender

Rev counter

Anything else you can think of."

His reply was a little scary, does anyone have an opinion, Ken is very experienced but times change is he correct.

"Hi Gary,

The fuel gauge, and sender unit and oil pressure sender are not polarity conscious.

The rev counter is driven by its own AC generator.

It should have heavy duty wiring and a volt meter, can you put a shunt on the ammeter to protect it?

Sorry, not very helpful but we are not insured for this kind of work, so avoid it.

You may have heard that 3 JEC members cars have burnt out when they fitted alternators and did not notify the insurance Company or have the car certificated by an Auto Electrician.

None had a pay out.



That one aside I wish to purchase clip on door mirrors anyone recommend a place ?

As always guys thanks for you help/input.


Alias Jagvette1 (on YouTube Channel)

Yes, he is technically correct in every point

If one does an alternator conversion, that theoretically means you can have more Amps flowing in your ancient wiring than it is designed for (for various reasons)

Therefore it is inherent on the installer to know which wires need to be upgraded
(not all by any means)

If one does not do this, not only do you increase the risk of a fire, but negate your insurance in most cases

The ammeter takes FULL current for most electricals, so it is and always has been a bit of an issue, so you can see why its a biggy for any conversion

others may disagree, or offer more detailed answers, but the JEC man clearly knows exactly what he is talking about

If you have gone as far as you said with all the parts you have purchased (or is this an inquiry?), in any case, all can be done, many on here have done it

You mention the oil pressure sender, Yes, they are not polarity sensitive but from my experience with my 3.8S owned for 50+ years they are often very inaccurate and failure prone. The best thing I did, after learning there is an identical Smith gauge that is mechanical, is fit one from Quality Classic in the UK, Not inexpensive but now the car finally reads accurate oil pressure. Highly recommended.

I definitely like that where can I get it ?



Yes I have purchased all I ‘Think’ I need, and I have replaced ALL the wiring with new (it’s one of my pet peeves when people want to keep the original fire hazard).

The wiring in the new harness that goes to the Ammeter is huge :slight_smile: (see Pic)

them ammeters are a fire hazard. what i did with mine on 65 stype was connect all the wires on ammeter together and replaced with voltage meter but kept the original shroud from the gauge instead and connect with any green wire behind dash.

1 Like

Sorry the supplier is Classic Quality not Quality Classic. See Ebay item;
154904973939. They have a website but I can not find this gauge kit on their site.

I got clamp on mirrors from Fosseway in the UK. I find them most eastheically pleasing & non intrusive i.e. no holes to drill.

You appear to be doing absolutely everying right, including your research

Therefore you are reducing the fire risk

If you document with pictures and specs, do you intend to inform your Insurance Company ?

I did not inform my Insurer when I replaced my Lucas 43Amp, with a Lucas 75 Amp, maybe I should

Think I only upgraded the main alternator wires, as the stock battery and Earth cables are well up to it.

I did recently replace the ridiculously short black positive battery lead with a longer bright red one, got so tired of struggling with a stupid 1" too short cable after 23yrs

It is retained for the next owner in a box marked “original parts removed”

great thanks

OK I shall check them out