4020 Diesel Light Switch

Anonymous-0 · Oct 5, 2008

Working on restoring the lights on my "new to me" 4020 diesel. All is well except that I have lights coming on when the key switch is in the ON position and the light switch is in the OFF position. All three of the other light switch positions work as they should. Just cannot figure out why some lights come on with the light switch in the OFF position. Should I suspect the light switch itself? I forgot to mention the lights that come on are the ones connected to the green wire (HD1 I think).

Thanks for your help,
-steve

Mike Aylward · Oct 5, 2008

Steve, if you went to the dealer and asked for "a light switch for a 4020" they may have given you one for a different serial number tractor. If memory serves me right there are at least two if not three different switches. I have an early 4020 and rewired it for a late 4020 switch so I didn't have to have the switch on to run the lights. Hope this helps. Mike

Anonymous-0 · Oct 5, 2008

24 volts or rewired for 12 volts makes a huge difference also.

Gerald J.

Anonymous-0 · Oct 6, 2008

The ignition is wired for 24 volts in series and the negative terminal of the left battery is grounded to the frame so there are 2 12-volt systems for the lights. The wiring for ignition and lights appears correct according to my wiring diagram. Just don't know why the HD1 terminal has 12 volts when the key switch is turned on and the light switch in the off position.

Anonymous-0 · Oct 6, 2008

This light switch was on the tractor when I purchased it. Are you saying that the newer switch is supposed to have 12 volts on the green (HD1) terminal with the key on but the light switch off? If so, someone before me may have swapped out the switch.

Anonymous-0 · Oct 6, 2008

yes, there are two 12 volt systems for the lights. If the negative post of the left battery is grounded, then the positive post of the right battery must be grounded.

And the left lights are probably on the left battery with the right lights on the right battery. Its important to keep the lights balanced on the two sides, so the charging will be equal. One set of lights will have +12 and the other will have -12. Odd light operation can come from faulty grounds somewhere. Or is there a ground wire incorrectly hooked to the opposite side 12 volt circuit? Polarity is important when chasing down the circuit and this wiring confuses many who then mix it up and wonder why it quit working.

What vintage is the tractor, that makes a difference on how its wired too?

Gerald J.

4020 Diesel Light Switch

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