MG Midget Forum

So I looked over past post from all forums in search of a way to know if my car is positive earth(61 midget so the way it came new) or negative earth.

I came across a post with the same question and he was directed to check the coil to distributor wire i.e. is the positive or negative going to the distributor. Mine has the positive.

Thoughts: The coil is flopping in the wind with no strap. So did the PO just hook up this coil the way he thought it should be but not knowing the car is a positive earth car?

Also, look at the battery leads and see which one is larger. Mine has the positive (larger one) to the body.

Thoughts: I would think you could stretch and shrink these enough to work on either terminal.

And last, the Tach which seems to be the main stick in the mud. It has been changed out from the original Jaeger Tach to a Smiths but not hooked up to anything.

Thoughts: Maybe the PO did understand the positive/negative thing and knew the Jaeger Tach would not work on a negative ground car or the PPO sold the Jaeger tach for righteous bucks and the new PO just grabbed this one.

SOOOOOOO if I hook up (and strap down) the coil negative to dizzy and get a Jaeger tach and hook up the battery as positive ground. What is the WORST case scenario?

David,

If the car has its original electrical system then it is a positive earth ground. All MG Midget's were a positive ground until 1968 from what I can discern. The issue is that if you hook it up with a reversed polarity (i.e. as a negative ground but its positive), you will know almost immediately. The moment you hook up that second cable, you'll cause a direct short in the system, this will cause that cable to arc weld to the battery terminal and if left there could cause a fire in the electrical system. This would lead to most likely catastrophic failure of the electrical system and replacement being necessary. The nice part is, if ya do fry it, moss does sell an entire replacement harness and the sub-harnesses as they call it for about 450 bucks total, so it is replaceable, and small enough to not be a huge pain in the ass. I would assume that the fact that you have a positive cable hooked directly to ground you have a positive grounded system, but without seeing it I couldn't tell you any more than that. I'll take some pictures of mine (I know its positive ground) and post them up here for you tomorrow if I can manage to remember to. Also if the smiths tach is a positive earth ground then it will say "positive earth ground" on it in little letters in the middle. The tach and fuel gauge were the only two that were specific to being positive earth ground, the other gauges being mechanical and not really needing electricity and all. Also a quick breakdown of your VIN indicates that the car is number 281 made…ever. The GAN1 is indicative of it being a Mk1 Midget, the L meaning left hand drive and the 281 being the body number built. Thats a pretty early model, which is pretty awesome, I'm kinda jealous . ya have a real nice car there, but be careful with electrical, that stuff goes south real fast. Also, check to see if you have an alternator or a generator, if its a generator its most likely positive ground, from what I can find they went to an alternator shortly after going to negative earth. The tach number should be RV1 2401/01 from what I can find. Also most of my data comes from "Original Sprite & Midget: The Restorer's Guide" By Terry Horler. It's an awesome book and only cost me like 45 bucks on ebay, strongly recommend it. Best of luck with the electrical system and like I said, I'll try to get picks of mine up tomorrow, the pertinent parts at least.

William

Well I can confirm that switch was made in '68. I can also confirm that when the DPO dropped a '66 1098 in the charge hooked up positive ground. Engine would start with gas fed into carbs but fuel punk would not work nor any if the instruments. A few day later after a lot of head scratching I realized things were hooked up backwards. Swapped cables and Vroom. Had to re polarize generator but other that that no issues. ymmv

I should add: no battery in car when I acquired it. All electronics except the tach is original to the car.
Yep William, the car is the 180th car off the line (they started at 101) I'm told the 3rd or 4th oldest know in the world and possibly the oldest left hand drive. Terry's book is a good one.
Jim- was that 1098 put into the frog eye?

As has been stated, the cars up until around '68 were originally positive ground. Except for any components that are made to be negative or positive ground only (like a radio) There's no issue reversing polarity as long as you depolarized the generator, and connect the coil accordingly. None of the original equipment will have any problem working either way. If you don't re-polarize the generator, it may not charge right, and the coil will work either way, it may just not run as well as it should. polarizing there generator is a very simple process which is covered in the original factory shop manuals. It's also recommended anytime you disconnect the battery, though it's seldom an issue.

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Gerard

http://gerardsgarage.com/

David
There was a 1098 installed in my '68 Sprite when I originally acquired and installed by the P.O. His yard held 5 Spridgets in various states of rusting.

My BE parts car I discovered does have a 1098 installed that is a locked up lump. Bugsy II my current ' 59 project came with a running when removed 948 with a rebuilt 4 speed that will receive a 1275 and a 5 speed. The 948 turns over by hand and rebuilt smooth case is available for sale. More funds for Bugsy II project.

This sounds much better than arc welded to the terminal, catastrophic failure,$450 wiring harness and up in a fire ball.
I am having the generator rebuilt. Do I need to tell him anything or just do the tap tap thing at the voltage regulator when I install?

Gerard is exactly right. No mushroom cloud will appear...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

My two bits..If your going to build a stocker...show car or down those lines.. might as well stick with + BUT if you start adding some of the neat stuff you see on this forum then most are neg. ground.... so you might as well doer now and move on to the next project... coil is easy neg ground neg post to distributor and visa versa...

Tach is the only thing and there is a WIKI on converting tach to neg ground. I've got it saved on my PC at home if you cannot find ping me.

I agree, I owned a ford anglia105e in my late teens, that the previous owner had changed from positive earth to negative earth, he had a new negative earth radio cassette player,he wanted to install so just changed the battery leads but didn't touch the Dynamo so the battery just went flat outside a pub with my new girlfriend sitting in it, all I had to do was charge the battery and swap the leads back, no explosion! And that was 25 years ago. Chris

If you are having generator rebuilt you would have to polarize it anyway, may as well go negative ground, no it won't go up in smoke, I've done this many times. I you ever want simple things like a power outlet for a phone charger, a radio etc. you will need negative ground as positive ground radios went the way of the dodo bird.

Ditto on the polarity. Had an early vette in the shop and we had no idea the battery was hooked up wrong until we went to diagnose the issue with the charging system. It will be fine, but youll wanna get it all straightened out after its running

factory went to use of negative earth as I prevented body corrosion
negative ions in atmosphere attacked positive body
neg ions not attracted to neg body
every thing british leyland made
Austin morris mg riley Woolsey triumph van den plas
Land Rover daimiler Jaguar rover went neg earth around 1971

Your original tach was mechanical, sometimes people had a hard time understanding that there was a gearbox on the back of the genny, sometimes the genny got replaced with a later, 'one size fits all' without the tach threads on the back, sometimes the cable just kept breaking (due to misrouting) and sometimes they just got 'upgraded'.
Get a tach that has whatever ground you want to run on the car, everything else aside from the genny will work just fine, Repolarize the genny if you're going to negative ground.-not a big deal to do.

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'58 Bugeye
'05 Mini Cooper S