Howdy everyone,
I have been trying to figure out why my back up lights are staying on in all gears. I have only found one thread on a different site that has the same issue as me.

I have ruled out everything else except for taking off the NSS and cleaning it. My only thought is that the NSS is stuck in the “on” position and I have to clean it. Anyone else have this problem? Would my solution work? Thank you

 

A little more info would help.

Manual or Auto?
Column shift or floor?

 

It is an FMX 3-speed auto with a column shifter. I also have some photos of what it looks like right now. I had someone go into the cab and click through all the gears and it does click through every one. Here are the photos

 

If you can not adjust it to work properly, then time to replace it.

 

You can test it also.
Follow the wires up to the connector, usually located behind the engine at the firewall, and separate the two halves of the connector.
With a volt meter or test light, check the body side connector.
With the key in ACC or ON (but best to use ACC) there should be power on only one of the black wires.
If you have power on both, then the fault lies upstream in the system somewhere and not the neutral safety switch.
However, as old as that switch looks, it’s very likely finally failed. If you need a new one, I would test it first. Make sure it looks like the correct one, with the correct connector, then with an ohm meter verify that the different positions work properly.
Nothing worse than installing a new part only to find out it doesn’t work. Which happens frustratingly frequently these days.

 

When you say test it with a volt meter, do I set it to ohms or AC or DC? I never know how to test wires on my truck.

 

Also, the connector on the body side of the NSS has 2 black wires going into one point. How do I know which one is good?

 

Update,

I disconnected the NSS and the lights were still on, so it is not the switch, what else could it be?

 

Well, that kind of sucks. Would’ve been easier if it was the switch. Oh well…
unfortunately, you’re just gonna have to trace the wires to see where they are shorted out. Without a diagram in front of me, I can’t even imagine where one power wire might be touching the other wire to the lights.
Should only be a single wire going back to the back of the truck, to the lamps themselves.
In fact, the first place to check might be the lamps themselves.
Pull the lenses off, check the bulb sockets and wires at the housing. I forget what year your truck is, but if it’s got the one piece plastic housings, you’ll have to remove them and pull the bulb sockets out individually.
If it’s an early style with metal housings and separate plastic lenses, pull the lenses off and see what you find.
Might just be rust in the housing, or corrosion at the connectors a few inches back.
Maybe someone tried to install trailer wiring and got it messed up. Usually, it’s an eye-opener to follow the wiring harness from the firewall back to the tail lamps. Almost always find something a mess. Sometimes it’s melted wires from being too close to a dual exhaust system, sometimes it’s a cut wire from some work previously done. Sometimes it’s bad trailer wiring plugs. Maybe even a pinch from a aftermarket gas tank. Hard to say at this point.

I forget if you said, and can’t see it from my phone while writing, but have you had this truck a long time? Did it just start doing this, or has it been a long time?

 

back to this anyway, you would need both DC 12 V, and ohms for different testing.
As you found already, with the switch disconnected in the key on, you use the 12 V DC setting.
If you want to test the switch, you change to ohms and then put the probes on both black wire contacts. Have someone row through the shift positions, or you can change it manually yourself and then go back out and test in each position, but you should see a connection between the two wires (zero ohms) only when the shifter is in the reverse position.
For the neutral safety portion, you would want to see zero ohms between the Red w/blue wire contacts only when the shifter is in park or neutral.

Doesn’t matter which one has power. It will only be one, and you simply use the voltmeter to find out which one. In your case you found out it was both, so you knew something was amiss immediately.
There should only be power on both when it’s connected to the NSS and it is in the reverse position.

 

So I disconnected the switch and cleaned all the grounds and the lights stay on. I took out the fuse and the lights shut off. I disconnected one of the wires out of a 3 wire socket and only connected it to the black/red and ground wires and they stayed on whenever I turned the ignition in the ON or ACC position. Am I still missing something?

 

Which 3-wire socket, where?
Which wire did you disconnect?
Which ground wire did you connect it to?

Paul