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View Full Version : TR2/3/3A Identifying positive or negative ground....



M_Pied_Lourd
10-20-2014, 08:16 AM
Hi guys,

Looking at a TR3A with no battery installed and trying to identify if the car has been converted to negative ground. Is there a quick way to do this?

Cheers
Tush

Brinkerhoff
10-20-2014, 08:34 AM
The neg. cable end is smaller and won't fit the positive terminal on the battery without opening it up. So check that first. The CB terminal on the coil is the wire that attaches to the distributor ( contact breaker) on a positive ground car. SW is from the switch. If the coils been changed out the positive terminal would go to the distributor,if its still a positive ground system. If its been changed to negative ground then the neg. terminal on the coil wire would go to the distributor.

Geo Hahn
10-20-2014, 09:38 AM
Of course you could just ignore what has gone before and 'convert' it to whatever polarity you want. Worst case is that it is already converted and nothing happens.

Of course you'll want to be aware of any polarity sensitive devices that have been added (e.g. a radio) and not offer them the wrong polarity.

TR3driver
10-20-2014, 10:06 AM
It's also entirely possible that someone hooked the battery up negative ground and didn't bother to switch the wires on the coil.

As Geo said, hook it up the way you want and go with it. Probably best to repolarize the generator as well, since you have some doubt and it certainly won't hurt to do it.

I don't think I've ever seen a TR3 that managed to keep it's original "helmet" cable ends since new. Has anyone else?

trrdster2000
10-20-2014, 01:29 PM
On some of the early radios there was a plug on the back to change polarity, so you can check yours. Not a lot of people knew about this and threw away the originals.

Wayne

M_Pied_Lourd
10-20-2014, 04:13 PM
Fantastic guys! Thanks for all the responses. It is appreciated.

Cheers
Tush

HerronScott
10-21-2014, 07:21 AM
It's also entirely possible that someone hooked the battery up negative ground and didn't bother to switch the wires on the coil.

As Geo said, hook it up the way you want and go with it. Probably best to repolarize the generator as well, since you have some doubt and it certainly won't hurt to do it.

I don't think I've ever seen a TR3 that managed to keep it's original "helmet" cable ends since new. Has anyone else?

Doesn't the ammeter need to have the cabling reversed if you switch polarity unless you don't mind it reading discharging when charging and vice versa?

I don't think my TR3 has the original helmet battery cables but one of my TR4A's does. Screws are MIA though.

Scott

mikephillips
10-21-2014, 12:16 PM
Yes, the ammeter wires need to be reversed if going to negative ground from positive.

TR3driver
10-21-2014, 04:02 PM
Doesn't the ammeter need to have the cabling reversed if you switch polarity unless you don't mind it reading discharging when charging and vice versa?

I don't think my TR3 has the original helmet battery cables but one of my TR4A's does. Screws are MIA though.

Scott
Wow, I didn't even realize they were still using them that late!

Yeah, ammeter leads should be swapped, but like the coil, not everyone does.

Geo Hahn
10-21-2014, 05:24 PM
Wow, I didn't even realize they were still using them that late!...

My '69 Jaguar came with them and still had them when I got it -- but they were pretty chewed up from years of battery chargers and jumper cables biting them.

glemon
10-24-2014, 06:11 AM
Geo, you beat me to it. My 67 BGT had them too, a bunch of them since it had two six volt batteries.

I remember when I reversed the polarity on my 4a and the ammeter read backwards until I figured out you can just switch out the two big wires going in on the back.

This could be another clue on the car in question provided the prior owner swapped it out when ( and if) they switched polarity.

Don Elliott
10-24-2014, 10:38 PM
Dave - You say you were looking at this TR3. Does this mean you have bought a third TR3A - to go with your parts car and your TR6?

Cheers

Don

M_Pied_Lourd
10-24-2014, 11:53 PM
Dave - You say you were looking at this TR3. Does this mean you have bought a third TR3A - to go with your parts car and your TR6?

Cheers

Don

Hi Don, yes I am afraid so :glee: I now own TS44836LO, a 59 3A

Cheers
Tush

toysrrus
10-25-2014, 04:24 AM
Hi Folks,

I was at the "Eurofest BMW Classic Car Show" last Sat. in Greer, SC (Great Show as usual). Over 400 cars there & only "European" marques.

There was an "Original, Un-Molested, Un-Restored" `58TR3 there with the "Helmet" cable ends in reasonably good cond.

Its too bad they did`nt have a "Preservation" class cause he would have won!!

Regards, Russ

thechileman
10-29-2014, 05:09 PM
Lol, I know this is hijacking the thread, but when I got my TR4, it had the "helmet" battery cables. I didn't even consider they might be of interest to someone. I think I pitched them. I replaced them with conventional cables when I switched it over to negative ground. I will look again in my junk box, and if they are still there I will post up and offer them to somebody no charge. I need to learn that when I think something is junk, I need to ask here first.