Reversed battery polarity on 8N

   / Reversed battery polarity on 8N #1  

frontman

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I had a brain freeze and hooked up the 12v battery on our '52 8N on reversed posts. Seconds later, wires were smoking and I pulled the connections. The starter motor turns but I checked a plug and there's no spark and there are no lights. This tractor was converted to 12v last year. Have I got only fuse damage or bigger news like the alternator?
 
   / Reversed battery polarity on 8N #2  
Hey Frontman,
I don't know about the 8N specifically but in general when you reverse polarity in a DC system you will cook anything that is dependent on a negative (or positive) ground , such as start motors, coils, etc. since they are dependent on the flow of electrons from only one direction. (Starter motors because power flowing the wrong way will run it in reverse) And the alternator, could be effected as its a similar to a electric motor and power flowing in the wrong direction might cause it to cook the internal wire windings as it fights to turn

As for the fuses, they blow when the power traveling over the filament is more than its rated for.

So if the motor cranks but you get no spark, I would check the ignition coil and see if it looks cooked. If its an electronic ignition, then I would bet that it's done for. The alternator would be the place I would look if the battery failed to charge or ran down after running it for a while.

HTH
 
   / Reversed battery polarity on 8N
  • Thread Starter
#3  
Thanks Jim. I'll check the ignition coil to start with. By the sounds of it, my starter motor is running backwards at this point.
 
   / Reversed battery polarity on 8N #4  
<quote>By the sounds of it, my starter motor is running backwards at this point</quote>

:D Unless there is a starter motor out there that stays engaged all the time, not likley. There are groves on the shaft that spin a cog into the flywheel. So if it ran backwords, the start motor wouldn't engage and it would never turn the motor over. :D
 
   / Reversed battery polarity on 8N
  • Thread Starter
#5  
Gotcha. So my starter motor is likely okay. Good to know.
Thanks again.
 
   / Reversed battery polarity on 8N #6  
I'd almost be willing to bet there's not too much damage other maybe a blown fuse or three, and maybe a couple wires that have burned themselves in two. The first thing I would check would be all the fuses, including a fusible link if it has one. Then, I would trace all the wires that got hot, those should be a clue as they were carrying the heavy current. I don't think you can really know what all else is damaged (if anything) until you make sure the fuses and wiring are good first. Good luck!
 
   / Reversed battery polarity on 8N #7  
Reversing the battery polarity is not the happy thing to do. All components that are solid-state devices are asuredly blown. The Diodes in the Alternator and Voltage regulator are most likely cooked, the electronic ignition module; any thing on the instrument panel that is solid state may be gone too. Relays, motors and lights should be ok. Check for blown fuses and fusible links.
 
   / Reversed battery polarity on 8N #8  
Jim.. it's apparrent your not familiarwith ford electrics.

our old starter motors spin the same direction no matter what polarity.. it's because the way the field is wired.

same with the ignition coil.. it will spark either polarity.. ( though best to run at correct polarity for optimum spark )

old n's had no alternator.. only a generator.. and they can run either polarity once polarized correctly.

now.. any alternators present are likel toast nearly instantly.. as is any ei modules if they were powered at the time the polarity swap happened.

soundguy

Hey Frontman,
I don't know about the 8N specifically but in general when you reverse polarity in a DC system you will cook anything that is dependent on a negative (or positive) ground , such as start motors, coils, etc. since they are dependent on the flow of electrons from only one direction. (Starter motors because power flowing the wrong way will run it in reverse) And the alternator, could be effected as its a similar to a electric motor and power flowing in the wrong direction might cause it to cook the internal wire windings as it fights to turn

As for the fuses, they blow when the power traveling over the filament is more than its rated for.

So if the motor cranks but you get no spark, I would check the ignition coil and see if it looks cooked. If its an electronic ignition, then I would bet that it's done for. The alternator would be the place I would look if the battery failed to charge or ran down after running it for a while.

HTH
 
   / Reversed battery polarity on 8N #9  
Once, when replacing the battery in an old 8N, I realized it was hooked up bass-ackwards... positive to ground... I'm not terribly smart but I had never seen anything like it so I set the new battery aside while I investigated... as it turns out, some are reverse polarity on purpose... it's just how the system was wired... Someone once told me that the only thing on the engine that care was the solenoid.... I installed the battery just like the old one against everything I had ever been taught and it works fine... jest looks funny.. lol
 
   / Reversed battery polarity on 8N
  • Thread Starter
#10  
If I end up with just having to replace a few wires and fuses I'll consider myself lucky. I'll start on that tracing first and then I'll see about the alternator. I won't get a chance to check it now until Saturday but I'll post my findings.
Thanks all...
 
 
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