Strange electrics...Help please

[Luap McKeever]

1940 9N converted to 12 volt system. New 12V coil, distributor, points, rotor, resistor and all. New alternator, battery.

Rewired it this morning because I thought it wasnt charging. Now, after re-wiring it, it does the same thing.

When running and when putting a voltage tester to the battery (positive on positive, neg on neg), it only reads 6.5 volts. Turned off, the battery reads 12.5 volts.

However, when running and reversing polarity (negative tester lead on positive battery post), It reads 13.5 to 14 volts.

What gives? Is this tractor positively grounded? Should I try swapping the battery cables?
Is it possible that the 12v coil i have has a built in resistor?
Can I just bypass the resistor? If so, how? Just hook the existing wires that run to the resister in with the ignition?

I appreciate any feedback. This one has me stumped.

thanks,
Luap

 

[Dell (WA)]

Lou......12v alternators DEMAND negative ground. DO NOT REVERSE or you will let the smoke out.

And yes, yer meter positive goes to battery positive. And you should read about +14v when running; NOT the 6.5v you report. I say yer alternator is BAD. Take it in to autoparts store for a "free" checkout.

Don't be fer messin' with yer "infamous ballast resistor". it aint'chur coil. .......Dell

 

[Luap McKeever]

Thanks Dell, but I just put this alternator on there yesterday. It's brand new gs 12 GM series. I rewired like this:

- one wire from alternator F to coil to resistor
- one wire from post on alternator with jumper to R on alternator to the amp gauge
- one wire from other side of amp gauge solenoid.
- ignition to other side of resistor
- ignition to solenoid
- Solenoid to starter

With it only registering 6.5, it makes me think that the coil has a built in resistor. Should I just bypass the resitor?

Also, I need to do some blading, will running it like this hurt anything?

Thanks,
Luap

 

[Bruce (VA)]

Take a look at your wiring diagram. You are confusing the charging circuit w/ the ignition circuit.

First off, as Dell sez, chances are very good that the alternator is bad.

As to the 12v coil & built in resistor....no, it doesn't have one. You should have at least one resistor in the ignition circuit (the OEM ballast resistor) and because it's a 12v conversion, probably one more. If not, you can expect to have a short life on the coil.
50 Tips

 

[Jubilee85]

I am with Dell, but I want you to look at the negative lead from your battery, is it bolted to ground/battery box/engine or anything like that ? You say that it reads 12+ volts with engine off, this is good - but flip your leads, it should read 12+ volts also ....but a - sign will pop up on your meter. I have heard about a battery being charged from the factory in reverse, caused a lot of damage in a RX-7 ...but that is rare. Also grab the lead from your alternator that should go back to the + side of the system, is it hot ? it should not be, if you had several lights on and a dead battey it might be warm, but a 2 volt push should not be enough to heat the leads. Do you have another meter too? One last thing - take your meter and place + lead on + lead of battery and other - lead on frame.....should get something like 14+ volts.
Might want to check all the wiring diagrams on this site too

 

[kilroy]

I aint a good electrician, but shouldnt the alternator power go into the resistor or the battery, then on to the coil? If you put in the resistor to lower the volts to the coil from the battery, but then hook the alternator in on coil, youve defeated the purpose of the resistor, right? sounds like you go from alternator to coil, then coil to resistor. I'm geussing you should be coil to resistor, and alternator to the switch side of the resistor or to the battery? dont know much about 12v change overs, mine works fine with 6v, so I can only geuss