1520 Engine Shuts Off When Turning On Lights, Very Occasionally

[toot77]

I have a seldom occurring intermittent electrical gremlin I would like to solve. I have a 1995 model 1520 that I have owned since new. Currently has 3500 mostly trouble free hours. Used mostly for mowing, snow blowing, and rototilling.

My problem is that very occasionally, the engine shuts off when I turn on the lights. On this tractor, you have to turn on the headlights before the hazard flashers so I think it is the headlights/taillight that does it, but can’t say for sure. It does this so seldom that I Haven’t been able to do any effective troubleshooting. It shuts off immediately so my hand is still on the light switch and usually can get the light switch back off and get the engine running before it actually comes to a stop. If the engine does come completely to a stop, it immediately restarts.

I am convinced the fuel solenoid is loosing its 12 vdc. It only ever does this while turning on the lights after the engine is running. The engine has never quit any other time. It only does this maybe 4 or 5 times a year for the past 5 or 6 years. No fuses have ever blown. I can sit in the garage all day flipping the switch and it will not do it. From the wiring diagram, the fuel solenoid is on its own fuse and the light switch is on its own fuse. Both fuses are powered from the key switch ‘on’ position. Battery was new last fall. I am puzzled. Any insight into this is appreciated.

 

[grcutter]

Can you post the 1520 schematic?
I looked at the 1920 and 2120 schematics which may be similar.
What I see is that the hot side of the fuel solenoid connects to the Instrument Panel connector and is next to the headlights on one side and the flashers on the other.
You might want to inspect this connector.
Could there be something loose inside the Instrument Panel?

 

[toot77]

Thanks for the reply, here is the 1520 schematic from my service manual for 1320, 1520, 1620, & 1720. Looks to me like +12vdc from the ignition switch 'on' to a fuse block. One fuse is a line to the fuel solenoid, another fuse is a line to the alternator, and the third fuse is a line sending +12vdc to the light switch.

 

[grcutter]

This schematic is similar to the 1920.
I see a connection from #21 to the Instrument Panel connector.
Right opposite this connection is a connection to the Headlight/Flasher switch but I can't tell which wire it actually is.
I would inspect this connector and inside the Instrument panel for something loose that may cause an intermittent short.
There is an outside chance that turning on the lights causes a voltage drop at the top end of the fuse box and causes the engine stop solenoid #15 to also see enough of a voltage drop to stop the engine.
Maybe measure the voltage on the input side of the fuse box with and without the lights on to get a sense of how big a drop is occurring when the lights are turned on.