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MG MGB Technical - Petronix and Positive Ground

Has anyone managed to run the Petronix with positive ground? I want to convert a friends car, but he refuses to switch to negative ground due to "originality" issues. (Do NOT mention to him that a Petronix is not "Original!)

Pete
Pete

Hi Pete,

Yes, I have installed the Petronix kit in my 65 "B" which I elected to keep positive ground.

It has been 2 driving seasons and I would not go back to points....keeps a good consistent idle and I guess with this in mind I believe it has improved performance.

Very highly recommended, cost was about $200 CAD

Regards, Dino
Dino Zappi

Dino

So what was required? By all accounts the petronix would be destroyed if wired with wrong polarity.

Pete
Pete

Pete,

Real simple, may take all but 1/2 hour, but take the time to clean distributor and make real connections.

OK, the current positive setup with points is;

The wire on the negative (-) side of your coil is from the ignition switch.

The wire on the positive (+) side of coil goes to your distributor (points).

A) Take out the distributor (much easier) to work on and place in a vice.(Distributor cap removed)
B) Remove rotor,points, condenser, wire to coil...have a look inside to make sure all is normal and clean and re-oil.
C) Install kit (as per instructions)

When you re-wire,
The black & white wire from the kit goes to negative side of coil

The black wire goes to ignition switch

The positive side of coil now simply is wired to the chassis (ground)

Replace rotor with a new one.

It's that simple.

Bit of an expert as I did both my 65"B" and 64 TR"4".

Now as far as a decent radio is concerned for positive ground systems,if this is in your mind,use an inverter which are about $60.00.

Let me know if you need more info.

Dino
Dino Zappi

Pete,

Your friend and I have something in common perhaps--I also kept the car positive ground for no other reason except originality. I know--it's seemingly crazy to get so wound up over something that so easy to convert but that's how we're wired. I'll use only Lucas points till they're no longer available.

Why would your friend want electronic ignition when he's not even willing to switch polarity?

Just my two cents.

Paul
Paul Hanley

I installed the Lumenition system after comparing it to the pertronix. The only reason I chose Lumenition in the end was availability from a local supplier.
Both were almost identical in the way they are applied, etc.
I remember vague mention of some differences if you install the Pertronix on positive ground cars.
The Lumenition I bought had complete instructions on applying it to either negative or positive ground, as well as how to apply it with ballast resistor coils. From memory, it was as simple as reversing a couple of wires and connecting one extra wire from the chassis. Should be just as simple for the Pertronix. They both work on the same principle.

I guess my point is, it can be done and your friend can be as stubborn as he likes about the polarity. Sorry I can't give you exact details on how it is done in your case.
D O'Brien

Dino:

Thanks. You are right, it is quite simple. Never occured to me to switch the input to the coil rather than the output.

Paul;

If we were rational beings, would we even be playing with these things? My friends car is actually a rather high strung race type engine (all done 30 years ago so its is "period") and he is tired of a high rpm miss that only goes away by replacing points and re-setting dwell. He already has a new distributor.

Pete
Pete

Pete,

If I didn't have my car to play with I fear I would become irrational! I do agree, If I had a high strung race enginge MGB, I'd go for performance at every angle. Sorry to get on a rant about original--your first post made it seem otherwise.

Have fun--go fast and please cure that high end rpm miss!!

Paul
Paul Hanley

Or you could just get the Positive ground model of the Petronix. avail from Moss and many others.
Carl W French

This thread was discussed between 12/10/2003 and 14/10/2003

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