Positive or Neg ground, should I switch?

[dvu101]

What are the good and bad of converting to negative ground?

I want to up grade my distributer and fuel pump and need to either stay positive ground or switch.

What are your thoughts?

Thanks Scott BT7

 

[tahoe healey]

I think the primary reason is the ability to use newer radios, cell phone chargers and GPS.

 

[Randy Forbes]

I'm not old enough to remember if American cars were ever positive ground, but I do know that for the 1968 model year, all (or most of) the British cars switched to negative ground. So they couldn't have been giving up much.

Think about being on a road trip when your fuel pump (or coil, condenser, etc.) quits, and the only NAPA in the small town you're in has off the shelf parts you need to get back on the road. What are the odds that any of them will be positive ground? Oh sure, NAPA can get it for you; but not until tomorrow.

 

[roscoe]

My reason for switching, in addition to the reasons already given, was because everyting else I work on is negative ground and it is too easy to forget to switch gears when poking around the healey.

 

[terp83]

Scott:

I switched my BT7 from positive ground to negative ground in 1987, with no known consequences then or since. My reason for switching was the limited availability of positive ground radios and CB's. I never got around to obtaining a new radio, and after the emergence of cell phones, I saw no real need for a citizens band.

Randy and Jon have given great reasons for not switching back.

Jerry

 

[Bob_Spidell]

WRT to replacement/NAPA parts, if you do any serious cross-country driving you should carry spares for the items mentioned anyway. If you're 100+ miles from the nearest NAPA/Kragen/AutoZone/etc. it doesn't matter if you're positive or negative ground.

 

[Randy Forbes]

WRT to replacement/NAPA parts, if you do any serious cross-country driving you should carry spares for the items mentioned anyway. If you're 100+ miles from the nearest NAPA/Kragen/AutoZone/etc. it doesn't matter if you're positive or negative ground.

Please don't turn this into another diatribe like the silicone brake fluid thread.

The topic is, if the original poster should convert his car to negative ground, and I merely stated an example in favor of it.

It was not my intention to provoke another argument from you, nor will I participate in one.

 

[shorn]

I think that adding a radio would be the primary reason to switch. Radio shack sells a cigarette lighter (plastic surround) that can easily be isolated and therefore wired either pos or neg ground for use as a cell phone charger or GPS plug in. I have not converted my 64 BJ8 to neg ground. I did add a radio under the glove box that is isolated in a plastic cover. Not a problem to do that, but probably would have been equally easy to convert to neg ground.

 

[Genos2]

shorn's right, I converted my '53&'63 back in the '70's so I could install modern radios. I left my'67 because it was ordered new w/Blauphunkt 2-band radio & I didn't know how to reverse tach leads at that time. Why not convert?especially earlier cars. cheers Genos2

 

[tahoe healey]

If you should decide to convert to neg ground (I did) you should post the change on the battery and somewhere under the hood to let others know of this change. Assume nothing 'cause others will assume pos ground.

 

[Bob_Spidell]

WRT to replacement/NAPA parts, if you do any serious cross-country driving you should carry spares for the items mentioned anyway. If you're 100+ miles from the nearest NAPA/Kragen/AutoZone/etc. it doesn't matter if you're positive or negative ground.

Please don't turn this into another diatribe like the silicone brake fluid thread.

The topic is, if the original poster should convert his car to negative ground, and I merely stated an example in favor of it.

It was not my intention to provoke another argument from you, nor will I participate in one.

You're right. My comments are more appropriate to a 'what do I need on the road' topic. Sorry.

 

[Bob_Spidell]

You may want to change your coil if you convert:

https://www.britishcarspecialists.com/pdf/coil-basics.pdf

 

[tahoe healey]

He means changing the connections not the type coil. There are a hand full of easy thing that need to be done such as re-polarizing the generator and the tack loop needs to be reversed. The whole thing takes 20 minutes and costs you nothing. I think there was a "made simple" on Jim Werner sight. Also on the MG sight. I have the references some where in my files if any one is interested. There is probably one in the BCF archives.

 

[GregW]

the tack loop needs to be reversed.

Scott is lucky, he got one of them older Healeys with the mechanical tach.

The whole thing takes 20 minutes and costs you nothing. I think there was a "made simple" on Jim Werner sight. Also on the MG sight. I have the references some where in my files if any one is interested. There is probably one in the BCF archives.

There are a couple threads here in the archives. Oh, Jim Werner's site was closed by AOL (nothing he did, they did it to a whole lotta people without much if any warning). John Sims was able to salvage almost all of it and that info is now on John's site. https://www.healey6.com/

 

[Bob_Spidell]

He means changing the connections not the type coil.

That's not how I read it:

"In a positive-ground coil, the secondary winding is in series with the primary winding. This will improve the spark at the plugs by 250-300 volts. If the external connections of the coil (CB and SW terminals) are reversed, the current will flow in the opposite direction and the auto transformer effect will be lost."

- and -

"The ignition coils in early British cars were designed to produce a positive-ground spark"

- and -

"If the car is converted to negative ground and if a negative ground coil is not installed, the 10 percent advantage is lost."

- and -

"If you change to a negative ground, it is always better to replace the coil with a negative system coil."

 

[Bob_Spidell]

Further, I'd always heard that positive-ground cars had more efficient ignition systems. This is due to "negative spark;" i.e. the spark jumping from the center to the outer electrode. I haven't found an explanation for this, but this site:

https://www.motorera.com/dictionary/ne.htm

seems to confirm it:

"Negative spark
A spark that jumps from the negative center electrode to the positive ground electrode of the spark plug, allowing a reduction in the high voltage required"


So, it seems positive ground is actually more efficient than negative ground. If you convert to negative ground you'll lose some efficiency in your ignition system.

 

[Legal Bill]

Bob,

You are right, but the theory never realy made much of a difference in practice. Negative ground cars fire just fine.

 

[Bob_Spidell]

Agreed, but it's an interesting curiosity to me; i.e. there's an actual reason for using positive ground. Supposedly, Henry Ford used positive ground for this reason for awhile, but there was apparently a licensing ($$$) issue so he went back to negative ground.

Norman does make it clear you should switch coils if you convert (makes it easier to find your parts at NAPA, too).

 

[GregW]

I never really gave it much thought. Makes me wonder if the racing crowd uses pos. ground. If your not using as much energy, there might be a weight savings there. I'd guess millions have been spent on research.

 

[Michael Oritt]

The supposed advantage to positive ground is something about electron flow, way over my head.

Unless you are a slave to originality I prefer negative ground if for no other reason than finding replacement parts for electronic ignitions is just a bit easier as it is more common. Yes, I know Pertronix and probably all the others have Pos ground units but they are not as common and in a pinch might be harder to find.

Plus the whole concept of "Positive Ground" continues to go against the grain for me.... It's simply easier for me to think in terms of "positive equals hot and negative equals ground".