Headlight wiring problem on craftsman 12hp tractor

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  #1  
Old 07-21-09, 08:17 PM
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Headlight wiring problem on craftsman 12hp tractor

Hi folks, had a question about a used tractor i just picked up. A Craftsman 12hp/38"cut model# 917.255511. Tractor runs good so far and I got it for a decent price, plus I have a 2nd. parts tractor.

What I discovered was the headlights were unplugged, further inspection revealed the plug by the muffler was melted and wires going to one headlight were melted too. So I headed over to my parts tractor, fixed the wires and plug up lickedy split.

Put a fuse in, hit the switch and vola.. let their be light and their was light. Only problem was I hadn't plugged them into the headlight sockets yet, just had the wires and bulbs dangling..

The minute I went to plug the bulbs into the headlight sockets (meaning) I minute I touched the metal frame the fuse popped !? And I popped a few more trying to track the problem.

It would seem if I isolate the bulbs from the metal frame all will be groovy. But under close inspection that doesn't seem to be the way it was originally.

Any help will be appreciated.

Thanks Wayne.
 
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Old 07-22-09, 06:12 AM
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Double check the model number. I see nothing on the Sears manual site for model 917.255511.

I am confused with the “touched the metal frame” statement. If you touch the connector to the metal frame you are creating a short and the fuse is working as it should. If the fuse blows when you connect to the bulb you most likely have a short somewhere.

Headlights on most 917 mowers are powered by low voltage AC power direct from the alternator.


See if your electrical system is the same as in these two mowers:

http://www.managemyhome.com/mmh/lis_...M/L0907110.pdf

http://www.managemyhome.com/mmh/lis_...M/L0707326.pdf
 
  #3  
Old 07-22-09, 07:09 AM
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Hi and thanks for the reply.

What I mean by touching the metal frame is when you plug the bulb & socket into the backside of the headlight grill. The sockets have these little spring loaded clips that hold it in position.

I checked things with my multi meter. No short at either light socket. Positive is isolated but negative attaches to ground thru the light sockets via the outer casting of the light socket.

The lights will work fine as long as they don't come in contact with any part of the metal frame, then the fuse will blow. Fuse will also blow with no bulbs only sockets plugged in.

The pdf you attached is the same one I have in the owners manual. The brown & black wire feed to the headlights.

Under closer inspection I could probably isolate the back plate from ground. The back plate is where the light sockets plug into and act as the back of the headlight housing.

Do you think this is a problem with the alternator ?

Thanks again.

Wayne.
 
  #4  
Old 07-22-09, 07:31 AM
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It sounds like the light sockets are shorted. Normally you would need a ground for the lights to work. But you say they work without being grounded. Check the "tabs" to see if they are "hot". They should not be hot if they are supposed to be grounds. If they are hot, sockets are wired wrong.
 
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Old 07-22-09, 08:04 AM
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Each socket should have two wires, both should be isolated from the outside of the socket and not ground through it. Each wire is both positive and negative since the supply power is AC voltage.

I checked things with my multi meter. No short at either light socket. Positive is isolated but negative attaches to ground thru the light sockets via the outer casting of the light socket.
I don't think this should be so...
 
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Old 07-22-09, 02:03 PM
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Originally Posted by BFHFixit View Post
Each socket should have two wires, both should be isolated from the outside of the socket and not ground through it. Each wire is both positive and negative since the supply power is AC voltage.



I don't think this should be so...
Yes, the alternator is AC but is converted to DC. The battery is 12 volt DC and the light bulbs are 12 volt DC.
 
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Old 07-22-09, 03:09 PM
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Originally Posted by indypower1 View Post
Yes, the alternator is AC but is converted to DC.
For the charging circuit yes.
Originally Posted by indypower1 View Post
The battery is 12 volt DC and the light bulbs are 12 volt DC.
Correct on the battery, however the light bulbs do not know AC from DC, they are a resistor/load, no different from those you screw into you house sockets.

As well, according to the schematic or comments from Airman. If you refer to the schematic, it specifically states 11 volts, 5 AMP [email protected] 3600 RPM. (Page 27)

However it also shows the black wire as connecting to chassis ground which I am not sure is the case.
 
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Old 07-22-09, 03:31 PM
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Text from page 27 of manual- http://www.managemyhome.com/mmh/lis_...M/L0907110.pdf
YOUR TRACTOR IS EQUIPPED
WITH A SPECIAL ALTERNATOR
SYSTEM. THE LIGHTS ARE NOT
CONNECTED TO THE BATTERY,
BUT HAVE THEIR OWN
ELECTRICAL SOURCE.
BECAUSE OF THIS, THE BRIGHTNESS
OF THE LIGHTS WILL
CHANGE WITH ENGINE SPEED.
AT tDLE THE LIGHTS WILL DiM.
AS THE ENGINE IS SPEEDED UP,
THE LIGHTS WiLL BECOME
THEIR BRIGHTEST.
 
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Old 07-23-09, 12:59 AM
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The lights normally run off AC voltage. I don't know what is happening, I don't think the lights even run through the fuse. I'm not looking at a diagram to see though.
 
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Old 07-23-09, 11:34 AM
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Well it is more of a diagram and not an actual schematic, and even though it states the lights are not connected to the battery, it clearly shows the lighting alternator and the black wire from the light sockets connecting to chassis ground, which is basically a buss for the battery circuit.

Been quite sometime since my basic electricity, but something about AC and DC voltage using a common ground just don't sound kosher

Airman?

 

Last edited by BFHFixit; 07-23-09 at 12:00 PM.
  #11  
Old 07-26-09, 08:30 PM
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Hi everyone and thanks all for the input.

I made a rubber seal to go around the headlight back plate, added a couple of rubber washers to isolate it from chassi ground.

Head lights seem to work fine.

Cheers
 
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