View Full Version : Positive or Negative Earth

04-08-2012, 06:46 PM
Pardon the dumb questions, but I'm a noob when it comes to TR's. I believe my 4A is a 66 perhaps a 67(haven't looked up the numbers yet). Is it possible I have a positive earth car? The car has been sitting for fifteen years and had no battery when I took delivery. How can I determine what polarity I have?

04-08-2012, 06:48 PM
Stick a magnet in it...
Honestly, someone will show up/
Probably if it has a generator it is positive?

04-08-2012, 07:07 PM
I believe all the 4A's were negative earth. My 65 is.

04-08-2012, 07:13 PM
My manuals say it's positive, but how can I tell?

Marvin Gruber
04-08-2012, 07:13 PM
I'm thinking 64 or 65 they changed to negative earth on TR's.

Andrew Mace
04-08-2012, 07:42 PM
On the off chance that such things might never have been disturbed or changed, you could look at the low-tension wires on the coil and see how they are connected. A somewhat easier way to tell might be to hook up a good battery, switch on the ignition and see where the ammeter needle goes. If, with any load (such as lights), it swings to the wrong direction (positive), then the battery needs to be reversed.

04-08-2012, 07:46 PM
I would suggest doing both of those things; since one may have been switched and the other not.

Or, since it is so easy to convert, just pick a polarity and then swap the wires at the coil and/or ammeter if necessary.

You may also be able to tell by looking at the battery clamps. The positive battery post is slightly larger than the negative post.

PS, after sitting for 15 years, you'll probably need to polarize the generator.

04-08-2012, 07:56 PM
Hmmm, some things to look for. Thanks. Currently the car is at my father's as I only have enough room in my garage for my bike, so I'll have to check later this week.

Geo Hahn
04-08-2012, 08:20 PM
If it has a radio... until you figure out what polarity it previously had, do not turn it on. Everything else commonly found will either work fine or (as noted in the case of the ammeter) work backwards.

04-08-2012, 10:18 PM
FWIW, my '67 4A is positive earth. I doubt anyone converted from -ve to +ve so it must have always been that way. So that would lead me to believe all prior TR's would have been +ve earth as well.

If you plan on using any modern accessories (such as a CD player) you will need to convert to negative earth.

04-08-2012, 11:20 PM
The TR4A owner's manual shows negative ground, though it's certainly possible that a mistake was made by the factory or dealer.

04-09-2012, 07:06 PM
Advance Autowire shows up to & including TR4 has positive earth.
TR4A is changed to negative earth.


04-10-2012, 10:12 AM
mmmm. Makes me wonder how mine ended up +ve. Sounds unlikely to be a factory error.

Since I don't know much about the history of my car I am beginning to wonder if at some stage parts from a TR4 were donated. With my untrained eye the car appears to be mostly original so it's anyone's guess. Anyway, I plan to switch over to -ve ground soon.

04-10-2012, 10:47 AM
Both of mine which have 1966 build dates are negative ground and one is very original including still having the original helmet battery cables.

Dion, my guess is someone changed yours to positive as they had seen the same misinformation Cozmo had seen which related to the TR4. It is not difficult to swap polarity on the cars with the exception of the radio and the original Triumph radios had a polarity switch on them to accommodate the change.


04-10-2012, 12:37 PM
Sounds unlikely to be a factory error.

John Macartney (who worked for Triumph for many years) once wrote of having a car delivered from the factory with wire wheels on one side, steel wheels on the other, and one of each in the boot!

Geo Hahn
04-10-2012, 01:31 PM
John Macartney (who worked for Triumph for many years) once wrote of having a car delivered from the factory with wire wheels on one side, steel wheels on the other, and one of each in the boot!

And, as I recall, someone took a punch in the nose over that one. I have considered doing that set-up on mine for a club event and see if anyone notices (I'm guessing they would not).

When I got my TR4 it had been 'converted' to negative ground just because the PO had put the battery in backwards. Remarkably even the radio worked (was sold to me as having a non-working 'original' radio) once I turned the battery around.