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Negative Earth Confusion...


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#1 carlnrtn

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Posted 02 September 2009 - 09:01 PM

Hi. I was just reading some stuff about converting from positive earth to negative. And now it's got me thinking. The Mini ran before when we picked it up. But then took the battery out (Mini is my brothers, battery was from my car). Put the battery back in at a later date, and it sounded like it was turning over (although not sounding quite right), and wouldn't get up and running. I obviously did what I was used to doing and put the battery lead on the positive terminal and earthed the negative. If this Mini was positively earthed, would this cause the starter to go backwards and the engine not start?

It's a 1982 Mini Mayfair 998cc. Thanks,

Carl

Edited by carlnrtn, 02 September 2009 - 09:01 PM.


#2 GreaseMonkey

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Posted 02 September 2009 - 09:05 PM

Your mini should be wired negative earth.

#3 carlnrtn

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Posted 02 September 2009 - 09:06 PM

Your mini should be wired negative earth.


Ah fair enough. Still a mystery why it wouldn't start then! I'll find out when it's back on all fours and the wiring isn't such a mess maybe. Thanks for the help!

#4 GreaseMonkey

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Posted 02 September 2009 - 09:12 PM

Sorry for the short reply I was trying to remember when they were wired Positive. I think it was just the 60s minis, not all though as some were negative.


When you say it doesnt sound right, what do you mean? Any apparent noises?

If you say it was running before, have you fiddled in the engine bay? Maybe a wire has come loose, look around the coil and dizzy.

Check for a spark if you still have no luck by taking a plug out with the spark lead connected and get someone to turn the engine over while you earth it against the block.


Seems a silly question but trust me it does happen, is there fuel in the tank?

#5 carlnrtn

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Posted 02 September 2009 - 09:36 PM

Sorry for the short reply I was trying to remember when they were wired Positive. I think it was just the 60s minis, not all though as some were negative.


When you say it doesnt sound right, what do you mean? Any apparent noises?

If you say it was running before, have you fiddled in the engine bay? Maybe a wire has come loose, look around the coil and dizzy.

Check for a spark if you still have no luck by taking a plug out with the spark lead connected and get someone to turn the engine over while you earth it against the block.


Seems a silly question but trust me it does happen, is there fuel in the tank?


Well I only tried to start it quick to see what it was running like. I'm doing all the suspension at the moment so rear subframe and everything is off. Might be something really obvious, but I haven't paid attention to anything in the engine bay yet. To my knowledge, nothing has been tinkered with or removed in the engine bay, but I had no part in the car for the first 2 as it was my mum's partner dealing with it untill he left. Will have a closer look when it's all rolling.

Could be absolutely anything though, the wiring in this thing is a state! Dead ends and chopped wires all over the place. New wiring loom me thinks!!

And yeah, there was fuel in the tank, drained a good 5 litres out the other day :D

I like the idea of how you test for a spark. Never heard that one before, but I'm sure it will come to good use in the near future!

Thanks a lot for the help.

#6 dklawson

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Posted 03 September 2009 - 12:07 AM

How long was the car parked? The nature of your first post implies that it was for quite some time. If the car was parked for quite a while the carb could be gummed up also.

When you check for spark as listed above, take one additional step. For your comfort... use a dry, clean, thick rag to hold the plug against an earthing point. If the plug wires are old and suspect there's a good chance you'll get a surprise if you don't hold the plug/wire with a rag.

One additional thing to do as a quick test is spray a short blast of starting fluid on the air filter immediately before your next attempt to start the engine. If the engine fires up and promptly dies, you have a fuel delivery problem. If it doesn't try catching at all, return to checking the ignition system.

#7 carlnrtn

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Posted 03 September 2009 - 06:03 PM

How long was the car parked? The nature of your first post implies that it was for quite some time. If the car was parked for quite a while the carb could be gummed up also.

When you check for spark as listed above, take one additional step. For your comfort... use a dry, clean, thick rag to hold the plug against an earthing point. If the plug wires are old and suspect there's a good chance you'll get a surprise if you don't hold the plug/wire with a rag.

One additional thing to do as a quick test is spray a short blast of starting fluid on the air filter immediately before your next attempt to start the engine. If the engine fires up and promptly dies, you have a fuel delivery problem. If it doesn't try catching at all, return to checking the ignition system.


Hi. Thanks for the help, but no longer needed. It is my brothers car that was looked at by my mum's ex. He went on about how it was all possible, whereas really he only concentrated on the welding at the front. Never took a proper look at it. Anyway, now we have stripped it down we have noticed that there is a lot more welding. At the moment, I don't have the tools or the knowledge to be able to do such a job, so we would have to pay someone else. Had a mechanic/friend that is good with classics come round this evening, and we have decided that for the money it will take (bearing in mind my brother is only 17 and doesn't have a full time job and is in college) and the fact I need my own car on the road soon, it's just not feasable to do it.
Thanks to everyone that has helped me out though!!

Carl




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