General TR Pos/Neg ground determination?

[JohnB]

So for the past couple of years I have been working on the mechanicals of a '59 Peerless which uses all Triumph running gear. According to the wiring diagram for it, it's a pos. ground set up just like the Triumphs are.

But today while in the trunk I noticed for the first time that the very old and very dead battery, which hides tucked in a rear fender, is wired as neg. ground. Now I have a problem. Does that mean that someone along the way converted it from pos. to a neg. ground or does it mean the last owner just put the battery in wrong?

Is there some way I can tell if it really has been changed to neg. ground? This car has not had an engine in it nor run for 20 years. What does changing over to neg. ground actually entail?

Any suggestions would be greatly appreciated!!!!!!!

John

 

[2liter4cyl]

If it is like the tr3, either way will work. Starting with the neg. gnd., disconnect the generator and touch a jumper to ;the small term on the generator. Just enough to establish polarity Then try the lights or something to draw current. If the needle swings to minus, You have it right.


If not what you want, reverse the battery, repolarize the starter, and re check. If now swings to +, reverse connections on back of ammeter.


Enough for now. Le

 

[Geo Hahn]

One thing to watch out for is if the car has a radio -- you don't want to offer up the wrong polarity to that guy.

My TR4 had a battery installed backwards by the PO just prior to sale. Ran fine but the radio didn't work. When I finally realized what he had done and undid it, the original Triumph radio worked fine - so sometimes you can get lucky, but don't count on it.

 

[JohnB]

It sounds like this is no big deal, except for polarizing the generator. Actually a running engine will be a ways away, so that can wait.

So is there any good reason for having a pos. ground on Triumphs? How come the British went that route back then? Why do folks convert to the standard neg. ground?

 

[TR3driver]

There was a theory at one time that using positive ground would reduce corrosion of the frame & body. I think that theory has been pretty well disproven by now, but as I recall it was quoted by Henry Ford (who insisted on staying positive when many others were going negative).

Main reason for converting IMO is compatibility with aftermarket devices, like radios or alternators. Plus to me, negative ground just seems more natural.

Years ago, a buddy of mine and I did a road trip with him in his MGA and me in my TR3A. We decided that it would be nice to have CB radios to talk back and forth while driving (this was long before cell phones became available). He mounted an old negative ground (tube) CB radio in his positive ground MGA by just isolating the chassis and running the wires to the appropriate polarity. Unfortunately, he didn't realize that there was a ground path through the antenna mount, which he hung on the back bumper. Somewhere in Ohio, things finally vibrated around enough to complete the path through the bumper, and his wiring harness erupted in smoke! Really did a number on it. We were able to cobble together enough to complete the trip, but he didn't have turn signals or brake lights until we got back home.

 

[trrdster2000]

Some of the radios had a plug that could be reversed to have either polarity. Last ones I can remember seeing were on TR4's.

Wayne

 

[sp53]

I think I remember the gas gauge worked backwards until wires on the back of gauge are flipped around, but not sure.

 

[TR3driver]

I think I remember the gas gauge worked backwards until wires on the back of gauge are flipped around, but not sure.

I believe you are thinking of the ammeter. The TR3 fuel gauge doesn't "care" about polarity (and will likely burn up if you reverse the wires). The TR4-onwards units will work wired either way.

 

[Vila]

I agree with what others have said above, including option polarity.

There have been numerous articles written about changing positive ground cars to negative ground on many antique car forms to include this one, the Antique Automobile Club of America (AACA) and others.

I have also read that the coil wires should be reversed, but have never reversed the polarity on any of the positive ground cars I have owned. I only run my cars configured they way they came from the factory and only use original options. The Bendix R2BT4 radio (an original 1962 TR4 option installed by dealers) has a plug on the top that you insert in one of two different directions for Pos or Neg polarity.

When I bought my current TR4 the previous owner had attempted to change it over to negative ground and use an alternator. The alternator never worked, so I changed it back to a Lucas 22700 generator, plugged the original generator control back in and it has worked fine ever since. The car even still has the original wiring harness.

If you decide to keep the car positive ground the only thing I can say is to put a easily identifiable label on the battery to remind yourself and let others know it is positive ground in the event you need to charge or jump start the car. Also remember if you ever need to jump start the Pos ground car from a neg ground car the cables need to be crossed, meaning your negative hot terminal goes to ground on the other car and your positive ground goes to their positive hot terminal (i.e. Pos to Pos and Neg to Neg).

 

[TR3driver]

Also remember if you ever need to jump start the Pos ground car from a neg ground car the cables need to be crossed, meaning your negative hot terminal goes to ground on the other car and your positive ground goes to their positive hot terminal (i.e. Pos to Pos and Neg to Neg).

And whatever you do, DON'T let the bumpers touch, or let anything metallic make contact between them. Doors are less of a concern, but still not a good thing to let make contact.

 

[JohnB]

Thanks for all the input.
I guess I'll go with the pos. ground configuration just to keep it all original.
And touching bumpers won't be any problem since the whole body and bumpers were made of fiberglass.

 

[luke44]

If you decide to keep the car positive ground the only thing I can say is to put a easily identifiable label on the battery to remind yourself and let others know it is positive ground in the event you need to charge or jump start the car. Also remember if you ever need to jump start the Pos ground car from a neg ground car the cables need to be crossed, meaning your negative hot terminal goes to ground on the other car and your positive ground goes to their positive hot terminal (i.e. Pos to Pos and Neg to Neg).

dumb question: if I undo the 2 terminals and just want to charge the battery, do I use red/positive and black/negative as normal? Does it matter when charging, if the cars electricals are disconnected? Tia,

 

[TR3driver]

dumb question: if I undo the 2 terminals and just want to charge the battery, do I use red/positive and black/negative as normal? Does it matter when charging, if the cars electricals are disconnected? Tia,

Yes, use red to positive and black to negative on both sides. It's fine to disconnect from the car while charging (but not necessary).

 

[Geo Hahn]

And if you leave at least the battery ground cable connected you can connect that charger lead (which will be red for a + ground car) to the block. If it is the last connection when hooking up and the first disconnection when removing then any spark will not be in the immediate vicinity of the battery.

Main thing is to keep your wits about you when doing these things with a positive ground car - can't operate on auto pilot.

 

[luke44]

And if you leave at least the battery ground cable connected you can connect that charger lead (which will be red for a + ground car) to the block...

I'll take your word for it but it just plain feels wrong. I'm gonna disconnect, charge the battery as per "normal" as Randall describes, and then hook it all back up. Thanks for the clarification guys.