Negative Or Positive Ground

[Anonymous-0]

My MH 444 hasn't been started for 6 months. I get an initial pop and then it just cranks. I removed the battery to charge it. When I replaced it, I hooked it up with a negative ground because every vehicle I have owned has had a negative ground. When I pull the wire out of the center of the distributor cap and hold it near the engine block and press the start button, I get a yellowish spark, not the fat, bluish-white spark that Jerry/MT says is necessary.

I read in my owner's manual that the tractor came from the factory with a 12V generator with positive ground. A previous owner replaced the generator with an alternator, so I'm thinking that that required a polarity change. Is there a sure-fire way to determine whether an engine should have a negative or positive ground?

 

[Anonymous-0]

Unless the alternator is special it is negative ground. It is possible to find a postive ground alternator or a floating alternator but they are not common in automotive sizes.

If the alternator was positive ground and you hooked up the battery negative ground, you need another alternator. The diodes are now all shorted and the solid state regulator is probably all toast. Wrong polarity should have shown a large spark when connecting the charged battery.

You need to be sure the coil primary has the same polarity as the coil. So the + terminal should go to the ignition switch and the - to the points and condenser. Then the ammeter needs the + terminal to go to the loads and the alternator with the - terminal to the battery positive terminal.

Yellow spark can be a sign of a bad condenser. I read that sometimes new condensers are worse than old ones.

Gerald J.

 

[Anonymous-0]

Thanks very much, Gerald, for the useful information.