Legal Bill

For years people have told me that one can use a power inverter to convert the power supply from a positive groud car for use with a negative ground sound system, without needing to insulate the car radio from the chassis of the car. This never made any sense to me, untill I read the attached article. But I'm no expert and I don't know if this is right or not. It just sounds good to me. If you really know your electical/electronics, I would appreciate your thoughts. If you are just throwing out a guess, please say so in your post.

http://mgaguru.com/mgtech/electric/et207.htm

dlq04

I know Barney; in fact, he's been to my house. When it comes to love, he certainly loves two things - MGs and himself.

MG used the positive ground system until 1968. Their reasoning was they believed it inhibited electrolytic corrosion. But the cars rotted anyway, be it the British climate or Michigan! The change to the more conventional negative ground system coincided with the introduction of the alternator-based charging system on the 1968 MGB. Likewise, the original coil terminals are identified by CB (for distributor Contact Breaker which would be positive) and SW (for ignition Switch which would be negative).

On my current car for originality and appearance sake I elected to stay with a generator, although it puts out marginal power compared to an alternator, and stayed with positive ground system since that is what it had. I elected not to install a radio (dead weight since they never got used in my other MGs).

But having said all that I am now plan to switch to negative ground (it only takes a few minutes to do it) because I also plan to install a cruise control system that is negative ground. I installed cruise in my prior MGA and I really miss it on long drives. Plus, after taking my one-and-only first place national award I'm swapping out lots of original stuff for upgrades.

Bill, as far as I can tell Barney's writeup is accurate.

Over the years I've always ended up converting from positive ground to negative in all my MGs and been happy afterwards. Unless you are going for concours I'd go negative ground.

Legal Bill

^Yeah, I know. I'm just looking for something that will avoid that. I'd rather keep it original if I could. I'd put in a sound system that could be easily removed if need be.

The only issue with changing over to negative ground is the re-wiring of the tachometer. I'm not sure I want to try that as I just spent big money having it rebuilt. I probably should have had them change it over to negative earth while they were rebuilding it. Now, I don't think it will be easy to change it over.

dlq04

Ah, electronic tach . . . MGAs don't have that. Bill, I would contact the place that did the tach rebuild and ask them how difficult it is to switch. Sometimes it's not the big deal one might think it is. A friend was telling me that after they put a Petronic's electronic distributor in an MGB the tach quit. To correct the problem they had to move a small coil of rolled up wire under the dash -- they were instructed to either expose it or hide it (don't recall which) but it certainly wasn't something anyone would think to do and sure enough that's all it took to fix it. If it is a big deal, then it sounds like you have the choice of leaving out the radio (my answer) or doing the convert box.

Legal Bill

My brother is like you. He does not care for radios in british sports cars.

My second idea is to build a nice sound systme into a box that would sit on the parcel shelf behind the front seats. I'd make it a quick remove system the comes right out of the car with a power disconnect. Maybe I'll just do that.

dlq04

Bill, Here's a name and number of someone who could offer good advice: Rick Ashley, 248-737-1978. He lives in the Detroit area. Rick is retired, he's chairman of the Windsor-Detroit MG Club (which has a couple hundred members), and more importantly he has published a book on electrical systems for our British cars.

Legal Bill

Thanks Dave. I'll give him a call.

raymo19

How many instances of "those bastards" are in this book?

Legal Bill

Yes, I should call it a converter.

MsPerky

So what happens if the ground is positive when it should be negative or vice versa? Does the sound system simply not work, or is there some kind of explosion?