755 Headlight fuse keeps blowing

[kmmn]

The 25A Headlight Fuse keeps blowing (previously it would only blow when it was running, but I fixed that... now it blows as soon as I turn on the lights). I disconnected the switch and put a test light on each contact. The Yellow-White wire showed a ground, but that should be the feed from the switch to the lights, so I'm pretty sure it's grounding somewhere. (The short when running sounds like it could be a wire that grounds due to vibration). I disconnected every connector, to see if I could isolate the problem. No luck there, so I assume it's in the main line and not a branch to a light. I opened up most of the tractor hoping I'd see a frayed wire, but no luck there, either. The only thing I can think of is to cut open the nylon loom and see if there is a damaged wire inside, but I really hate to do that, since then I loose some protection for the wires. I really thought the short would be obvious. Has anybody had a similar problem or have any suggestions? Thanks!

 

[Rara Avis]

Here is your lighting circuit operation
View attachment john-deere-655-755-855-955-756-and-856-compact-utility-tractors-technical-manual.pdf.2.pdf

 

[beenthere]

kmmn
:welcome: to TBN

To find a short, make up a 12 v bulb to put in the fuse slot.. the short will cause the bulb to light and allow you to lift and trace/move wires around to locate the short (when the bulb goes out, you will have found the short). Saves trial and error and blowing fuses..

 

[Spanner]

That loom has a 'chafe-point' at the left rear corner of the pedestal (Steering column/console assy) where it goes down and splits rearward to the rear lights, fuel tank, seat etc.

You might have to remove the seat and the Operators Platform, mudguards etc to expose the chassis and the loom where it runs inside the chassis rail but exits to branch upwards to the console (and the light switch).

I had one chafe through there anyway. Devil to find but very satisfying when fixed.

Good Luck.

:wrench:

 

[kmmn]

Thanks for the responses. I have the full diagram, but this is easier to read, since it only has what I'm concerned about. I never thought of attaching a light to the circuit. I'll check for the chafe. I thought I found one going to the hood mounted headlight, where the loom contacts the engine (the paint was worn on the engine), but the loom looked ok. Thanks!

 

[cabover4us]

Don't let the condition of the loom steer your decision to check, wires continuous use of bending in a juntion won't show up in the loom condition, wires can Frey and separate inside the loom.

 

[kmmn]

Update... using the bulb wired into the fuse location worked and suddenly it stopped (not sure what happened). I tugged on various wires for a while and no short, so I plugged the lights in and threw in a fuse... still good, so I put it back together, knowing that the problem isn't fixed, but I needed to cut the grass. I was afraid to turn on the lights, but I had the tractor out tonight and it was getting dark, so I turned them on and one second later the fuse blew. Since I was getting the short with no lights or the switch connected, it's somewhere in the wiring run INSIDE of a loom, so cabover is right... the wire (probably 2 wires) is/are chafed inside one of the looms. This should be fun.

Thanks for the replies... they all helped!!!

 

[kmmn]

I found it while checking the oil pressure switch (separate problem). Two wires inside the loom behind the alternator wore through the insulation and grounded the headlight circuit... now onto other problems.

Thanks for all of the replies... they helped!!!

 

[Spanner]

Great news!

 

[Davidb1stein]

I know this is an old post, but feel that an update is needed.

I also have a 755 that was blowning the headlight fuse and based on the comments here found started to checking the wiring harness around the alternator where the wire was shorting out to the alum cover on the housing. Redressing the wiring harness away from where it was rubbing and covering with electrical tape. No more short, and working headlights.