Positive convert to negative ground?

[mine]

Fellow tr3Aers,
I have read some stuff on how easy it is to convert the tr3a from positive ground to negative ground? True? I do not want to fry my electrical. /bcforum/images/%%GRAEMLIN_URL%%/mad.gif I want to switch it so I can put a radio in. My father is now a member also. He goes by originalowner

 

[Geo Hahn]

True. So easy that the PO of my TR4 did w/o meaning to -- he installed the battery backwards and the generator re-polarized itself when it started the next time.

I don't recommend that brute force approach but the usual method outlined many places (incl the Moss catalog) where you 'flash' the generator connection works fine.

The ammeter will read backwards until you reverse the connections on the back but doesn't hurt anything to run it that way until you can get to it.

 

[martx-5]

You also have to reverse the connections on the coil.

 

[Andrew Mace]

There's a good summary article on the VTR web site.

 

[mine]

Hahn,
Thankyou for the input. I'll try it! /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

 

[mine]

Art, Thanks I'll reverse 'em!

 

[mine]

Andy,
I'll check Moss motors. They are pretty handy.
David

 

[TR3driver]

But watch out for any aftermarket accessories; like an electronic ignition or radio. Some of them don't like negative ground.

 

[angelfj1]

what is the benefit of converting and why did they use pos. ground to begin?

 

[Twosheds]

The only reason for converting positive ground to negative ground would be to use a modern radio. But who wants to listen to recorded music when you can listen to a lovely exhaust note?

I put an oil temp gauge in my old TR3 racecar but could never get it to work. Might have required a negative ground, like Randall suggests. Diodes and whatnot, don't you know.

Oh, and as for why they chose positve for ground to begin with, I don't know. It makes no difference whatsoever, so choose one and go with it. Henry Ford chose positive ground because Tom Edison told him to, and Ford just went with it.

 

[Exotexs]

there's a certain procedure to convert to Negative Ground other than just reversing the battery cables and hoping for a miracle...it just doesn't happen.

the only technician I know that has valuable online information about how to convert to Negative Ground is Mike Martinez of Star Auto Electrics in California, they rebuild Lucas Generators or Alternators after you fry it due to incorrect conversion procedures.

https://www.starautoelectric.com

 

[martx-5]

there's a certain procedure to convert to Negative Ground other than just reversing the battery cables and hoping for a miracle...it just doesn't happen.

the only technician I know that has valuable online information about how to convert to Negative Ground is Mike Martinez of Star Auto Electrics in California, they rebuild Lucas Generators or Alternators after you fry it due to incorrect conversion procedures.

https://www.starautoelectric.com

Perhaps you could link to the tech article on Star Electric's site that discusses converting to negative ground, as I was unable to find it.

Besides, the link to the VTR article was very explicit in what to do. As far as changing over from positive to negative ground on a TR3, the procedure IS very easy, and nothing will fry if you just change the polarity on the battery, unless you have a positive ground radio, or other positive ground electronics. Highly unlikely in a TR3. The only thing that might be a problem is that the generator will not function. In that case, a simple quick polarizing will get that going. The other two items that need attention are the ammeter and coil wire reversal. That's only if if you don't want the ammeter to read backwards, and the coil to be down about 15% output in secondary voltage.

 

[martx-5]

what is the benefit of converting and why did they use pos. ground to begin?

As Twosheds pointed out, converting will allow the use of a modern radio, as they are all negative ground, and the other reason is that you can use an alternator. If you are adding things like electric fans and fuel pumps, this will be necessary, as the original generator was hard pressed to supply 22 amps of current. Besides, if you pick the right alternator, they are readily available at any parts store for a song.

 

[Geo Hahn]

Even modern radios can be made to work on a positive ground car. I isolated the radio/tape deck circuit on my TR3A 20+ years ago and have had no problems with it. Of course, in addition to isolating the unit you also have to isolate the antenna.

On the TR4 that had the battery installed backwards... I really expected the original positive ground AM radio to be toast, but even it worked fine when the correct polarity was restored. Gotta give credit to Bendix for that one.

Henry Ford also chose to put the steering wheel on the left (in the US), fortunately that idea has stuck around.

 

[Exotexs]

ok, here's the link for the polarizing procedure to convert to Negative Ground:

https://starautoelectric.com/Technical.htm

An obvious benefit after converting to Neg. Ground that nobody has mentioned is: jumping the battery in an emergency. You can't jump from one car to another if the good battery is Negative Ground and the dead battery is Positive Ground.

I converted my '65 Jaguar S type to Negative Ground following Mike's instructions after I asked him about the conversion procedure found at the Jaguar Club of North America's website which incorrectly stated that: "the Terminals at the Generator should be shorted and that re-polarizes the Generator from Positive to Negative Ground".

Mike told me "don't do THAT! you will smoke your generator".

He sent me instructions on how to do it at the Voltage Regulator, which I did. He also insisted that a new battery should be installed, which I also did. Mike knows his stuff, he makes a living at rebuilding Lucas. The conversion was succesful and I am of the opinion that all the electronics in my car are more "lively" after converting. don't ask me why, I don't know, but the lights are brighter, the car starts faster, period. Yes, I had to invert the Coil wires, and the Ammeter Wires. Everything else stays the same and I installed a modern stereo without any worries.

Positive Ground may have been fine up to the 1960's, but in modern times, I don't want to be worrying about which of my two Jaguars is Positive or Negative ground, since all cars are Negative Ground nowadays. Today they are both Negative Ground.

good luck -
Ex

 

[TR3driver]

You can't jump from one car to another if the good battery is Negative Ground and the dead battery is Positive Ground.

Not true. I've done it more times than I care to think about. All you have to do is be sure that the two cars don't touch each other while the cables are connected; and connect positive to positive, negative to negative. IMO a good procedure anyway /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

While isolating the radio IS possible, I wouldn't recommend it. If you do that, any contact between the metal of the radio or antenna and the body of the car will cause a short. Friend of mine burned up the wiring harness in his MGA that way ... lucky it didn't set the car on fire. We still had fun cobbling the damage up enough to get home from 1000 miles away.

BTW, postive ground electronic ignitions have been available from the 50's; and still are available. Some, like the Crane XR700 are now "bi-polar", but some (like the Pertronix) still are not. And my latest TR3 project had a positive ground radio under the dash when I got it.