TR2/3/3A Changing polarity on TR 3

[DeanTR3]

Yesterday I read an online article about changing polarity on a TR-3 from positive ground to negative ground. I have two questions, how many of your have made this conversion and are you happy with the results? The article says you only need to change 4 things; the battery terminals, reverse rthe leads on the coil, reverse the leads on the ampmeter and change the polarity of the generator. What about the battery, will it run just as effectively with either negative or positive power? Thanks for your help. Dean TR-3A

 

[NutmegCT]

I never found a need to change the polarity. But the battery doesn't care about polarity as long as the rest of the electric system is set up and wired correctly (including the battery cables).

The battery remains positive + and negative - regardless of the car's polarity.

 

[TR4nut]

Yep, the battery remains as is - you'd only change it out if you prefer the poles to be in a different position when its sitting in the battery tray - but after the switch, the negative pole will be grounded to the car.

 

[glemon]

I have done the switch on a number of cars, including a TR4A, MGB/GT, AH100, and more than one Sprite, it is as easy as the instructions say (a little more complicated on some later cars with electronic tach but still pretty easy), makes it easier to run a modern radio or other accessories designed for negative ground cars, other than that I don't know of a reason to do it, but if you want to add the accessories no reason at all not to, completely reversible if you or the next owner decides to go back to original. I once tried to wire up a negative ground radio in a positive ground car by isolating all possible grounds, now that was not a good idea, and one afternoon many years ago all of downtown Lincoln NE thought that funny little foreign car with all the smoke coming out was on fire, and it nearly was.

 

[TR3driver]

I once tried to wire up a negative ground radio in a positive ground car by isolating all possible grounds, now that was not a good idea, and one afternoon many years ago all of downtown Lincoln NE thought that funny little foreign car with all the smoke coming out was on fire, and it nearly was.

Been there, done that! Fortunately (for me) it was a buddy's MGA that was smoking and we were able to hot-wire it enough to finish the trip (by not driving after dark).

I have converted all of my TRs to negative ground, and never regretted it in the least.

One more thing to watch out for; if you don't convert, be very careful when jump-starting from a negative ground car. Anything that touches metal-to-metal with the cables connected (like opening a door and touching the other vehicle) is going to cause a major short and might even blow up a battery.

Note that you don't have to actually change anything on the generator, just repolarize it. One easy way is to disconnect the wire from the F terminal at the regulator (ignition off, engine stopped), and brush it against the A terminal. If you see sparks, the job is done. Often it will even repolarize itself (battery leads swapped by accident), but there is a certain amount of electrical violence involved and I don't recommend it.

 

[Geo Hahn]

I have retained positive ground on both my TRs simply because I never had a need to change it. The usual reasons are a desire to fit a modern sound system or to convert to an alternator to power high-demand accessories.

So easy to do that the PO of my TR4 did it for me (nice guy but electrically clueless) by installing a new battery backwards before shipping the car. Amazingly not only did generator re-polarize itself but the radio was not harmed (worked fine once I put the cables back the right way).

You may find that the difference in battery post diameters may require some spreading of the connectors to fit.

 

[Vila]

I never saw a reason to change to negative ground, since I keep my cars all original including the radios.

If you have a radio you will also need to change the polarity of that also, assuming it has that capability.

The only reason I could see changing from Negative ground on my TR4 would be to add a more modern radio for something else that required Neg ground, but then again that is not my thing.

Visit my new and improved website at: https://jakegingervila.wix.com/bobs-vintage-cars-

Vila
1933 Chevrolet
1962 Triumph Tr4
1984 BMW 633 CSi

 

[TR4nut]

If you ever contemplate using something like a GPS, make the change. A friend of mine tried to isolate his GPS and keep his Triumph positive ground. Worked well until the GPS case accidently touched part of the metal dash. Instantly fried the GPS.

 

[FordFiesta]

Having positive ground may, in the future, prevent a not-so-friendly insurance company from installing a driving-habit and mileage recorder on your car.
(Remember: It's not paranoia if they really ARE out to get you...)

 

[TR3driver]

Having positive ground may, in the future, prevent a not-so-friendly insurance company from installing a driving-habit and mileage recorder on your car.
(Remember: It's not paranoia if they really ARE out to get you...)

Or you could just switch back if they do. "That's the way it is supposed to be."