New Member needs help with lights

Hello, I bought a 4020 at auction this spring and am trying to fix it up before it starts snowing this winter. I'm currently replacing the front axle, working on the loader, and trying to repair the lights. That's where I've hit a snag. The tractor is a synchro range with serial number 135,727. It has already been converted to a 12 volt system. The lights wiring was completly shredded from the six pin harness to all 5 lights. I have that replaced. I can get the rear tail light, flood light to work. I have the bright inner lights working. I cannot get the outside fender floods working though. The six pin harness only has 5 wires going in. Ive used 3 of the slots for the rear tailight, rear flood, and inside fender lights. I think the next two wires in that connector should run the outside floods and flashers. I'm not going to install flashers. Those wires will show 12 volts until I hook the lights up to them. I've made a jumper wire going straight from that connector to the light bulb. I have my ohm meter in series with it. As soon as I touch the wire to the bulb I loose the 12 volts. Take it off, get 12 volts back. I'm also trying to get my dash light to work. It acts very similar to the above problem. Any suggestions or ideas would be appreciated. Is the light switch bad? How to check it? Was the 24 volt transition not finished, etc?

Pictures of the harness

Here's a sort of generic diagram, there may be some differences by serial number or type of tractor, but the idea is the same, you MUST have 12 Volts at BOTH the ''A'' connector and the ''B" connector on the ignition switch, then both power sources pass through circuit breakers and on to the ''BATT A'' and ''BATT B'' terminals on the light switch.

Check for power there.

And DO NOT use your Ohmmeter on a powered circuit!

I read your post twice. You say ohmmeter,
can I assume you mean a multimeter used as
a voltmeter? A voltmeter has to be
connected in parallel, you may be getting
the wrong reading due to the voltmeter
circuitry. Wire from plug, through bulb to
ground and see if it lights.

As mentioned you do not use ohmmeter on powered circuit.

Volt meter reads voltage, ohmmeter reads resistance, and current meter reads current through the circuit.

Looking at the picture, if it were mine I would get a small screw driver or pick and clean dirt out of the switch and then spray with electric contact cleaner available at auto parts store. When it dries plug 2 halves together.

Then, according to the diagram HD2 (Head light) feeds your outside lights AND the dash light.
HD2 is fed from BAT A input on the switch. So with plug connected (you may have to turn on ignition switch to feed light switch) check for voltage at BAT A on light switch. If no voltage check back through wiring toward the battery and find your open connection.

If you have voltage at BAT A with light switch on check for voltage at HD2. If you have voltage at BAT A but not HD2 you likely have a bad switch. If you have voltage at HD2 then check wiring from switch out to your outer lights. Problem should be broken wire or bad connection, burned out bulb or bad ground.

Not understanding your test method of using your
VOLT meter in a series to test a circuit. You need to
ground the black lead on a good ground. Then test for
power with your red lead. If you still have the same
result of losing power, the power you are seeing is
going through some type of source with resistance like
a light bulb or a poor connection. A poor connection
would be less likely to restore the voltage after the
head light is unplugged but it can happen on rare
occasions. Looking at woreouts diagram I would look
to see if the dash illumination lamp is on when you
plug your light in, just a long shot. If this is happening
you will have to figure out what is wrong with the dash
lamp circuit.

Thanks for all the replies. Jargon has never been my strength. I was using a multimeter. I had it grounded at the negative battery post. I could make the outside floods work by powering it through a different pin. I forgot to mention the upper circuit breaker would drop voltage on one half at the same time the pin would. I know enough about electricity to either be useful or dangerous, just depends... I think I have enough to run some tests tomorrow morning and report back. Just fyi, the white connector in the picture is currently brand new with all new wires going to new bulbs. I used those pictures to show brillman what I needed to make sure I recieved the right harness. Another detail I left out is the remaining pins I have to choose from don't seem to have power in all three positions. I have a hunch my switch is bad. If anyone knew the for sure way that connector is supposed to be fed that would be a big help. For example, top left pin feeds brights, etc. Me and my MULTIMETER,have deducted my current configuration. I'll use your guys tips and get back to you. Again, thanks for the replies, forums like this are priceless.

Are all cavities used in your 6-pin connector, the diagram from SM-2039 shows 5 used.

This post was edited by wore out on 08/05/2023 at 05:35 pm.

Only 5 of the cavities are being used.

Why not install LED light pods and wire it however you would like? I bought some cheaper ones from Amazon (auxbeam I think) and installed 2 on the canopy, 2 on the loaded frame and 2 pointing out the back. They are so bright it might as well be day time! They came with install kits- wire, relays and switches.

Someday I might install a light bar, but
am going to wait and see how much I even
use the lights. The original system will
get me through for now. Im going to
replace the light switch. There seems to
be a problem at hd2. That one sends power
through that spring. I have power until
any load is applied. Whether that be the
original circuit or a jumper wire with a
single light on it. Could you guys advise
what switch I need. I see there are lots
of options.

Thanks for your diagrams they helped take
the guessing out of it.

Final update. I was wrong that the light switch was bad. It ended up being the upper circuit breaker. Replaced it. Solved my problems.

. Thank you for the update, letting us know the problem was solved .