John Deere 4840 Light Issues

John Deere 4840 Light Issues Problems

John Deere 4840 Tractor. I don’t have taillights or interior fender lights. I have replaced the light switch and the three relays under the steering wheel and still no luck. How to solve this problem?

  • Check the light switch and the wires going to it. I blew out a light switch on my 4040 because the insulation was gone in a section of the wire under the floor board that goes to the dimmer switch. I’m not sure if it wore out on its own due to vibration, or was helped by a mouse.
  • If there is no power to the switch or relays, then you are most likely having trouble with the circuit breaker. If there is power at the switch and the relays are activated, then before doing anything else, check the main harness plug under the front right corner of the cab. Often times the contacts in that plug develop a bad connection. The dimmer switch only controls the interior headlights and flood lights overhead in the rear. The lower taillights are separate from any of the dimmer switch circuits, so if they don’t light up, you’re having trouble and it doesn’t include the dimmer switch. If it is only the inner front and upper rear that are not working, then as mentioned above it could be the dimmer switch or the plug on it.
  • Also check the socket on the back of the headlight switch. I changed the switch once on the 4440 only to find it was the plug, and not the switch. Bad contacts there will also create burn marks on the back of the switch that will make it look suspicious and will burn the poles. If that’s the problem, it’s a PIA to change, and you’re going to make up some new words.
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