Electrical Short

[rooftrussman]

This is a Ford Tractor 1210 diesel, circa 1985 but should be generic. What I'm getting at is that the wiring is pretty basic. I have a fairly major short from the positive of the battery to the ground. This is without the battery attached. I've pulled the harness,the switches, the alternator, the regulator and the starter. I had the altermnator, starter and regulator checked, (needed a rebuilt alternator, probably fried it with the short). I'm now getting ready to reassemble it after I check the harness for shorts but that's just wires. Can anybody suggest anything else that might cause a short. I have the lights disconnected. I can't think of anything else electrical. I hope I covered all the bases. Thanks for any thoughts.

 

[Bill_C]

Do you have an ohmeter? If not go somewhere and buy a cheap one. All you need is something that will tell you if you have zero resistance or lots of resistance.

Then start at the positive cable. Follow it to the starter relay. Unscrew the cable from the relay. Use the ohmeter at the relay end of the cable to see if you have a short to ground--one probe on the cable end, the other to ground. A short will show up as zero ohms. No short there? There's a wire that also goes to the starter switch. Check it next. Go through the whole electrical system, item by item, with the ohmeter, using the schematic as a guide.

"Shotgunning" the problem (by just merely replacing components) is an expensive and frustrating way to solve a problem. A methodical search with a meter WILL find a short. I've got a 1100 and you're right, the system is simple.

 

[zzvyb6]

Hook your welder up to the leads and turn up the volume until the heat gives it away.

 

[Soundguy]

A test lamp and the battery is all you need, and is non destructive. Hook battery negative up, then insert test lamp inline with the positive... if the lamp lights.. you got a short.. start running the harness and find it..

soundguy

 

[rooftrussman]

The lamp sounds pretty good but not near as interesting as the welder. Maybe that would be a good way to fix the crack in the FEL.

 

[tommu56]

I use the divide and conquer method to find a short.

locate any plugs on the machine leave them connected use and ohm meter or lamp as described previously disconnect one plug at a time till you find branch
with short then follow that branch looking for short.
Usually a wire rubs through to create it.

tommu

 

[JSharp]

Hook your welder up to the leads and turn up the volume until the heat gives it away.

Many years ago I was in an imported car repair shop and they showed me a "short finder" they used on British cars. It was a solid piece of brass the exact size of a 3AG fuse.

They said it worked every time.

 

[rooftrussman]

I've made some headway on my short issue. I'm down to one last area, the starter. I tore that apart and it all seems to specs except when I run the "field coil ground test". It says there should be "high" resistance between the brush field coil connector and the starter frame. My meter says .5 ohms which doesn't seem very high but the repair place says it's normal and the starter has "plenty of power". It's amazing all the stuff in the starter in the way of grass, wasp nests etc. There was a mud dauber tube between the field coils. It seems that this couldn't be good but hate to spend the $ 235 and find out it was OK.
Any thoughts are greatly appreciated.

 

[randy41]

i may be asking something really stupid but what happens when the battery is hooked up and you try to start the tractor? when you say there's a short with the battery disconnected that means you hook up an ohm meter to the + and to ground and it reads zero ohms? and the reading when you do this and turn the ignition on?

 

[Bill_C]

The repair place must've misunderstood you, or else I'm misunderstanding you...the field coil shouldn't have continuity to the frame, I think there's your short. One of the wires on the field coil has a bare spot, or melted insulation, or an internal connection is shorting to the frame.

0.5 ohms isn't "high" resistance, it's (darn near) a dead short!

edit: You've disassembled the starter per the Ford manual so you've got the coil connectors exposed?