Neutral Safety Switch 904 reverse lights not working.

[Bruceynz]

Hi Guys,

Ok I am stuck, my back up lights (reverse) don't work, I know the 2 outside pins are suppose to short together when in reverse to turn the lights on, with the car in reverse the switch does not close (I have been under there with my meter) So the trans is an early 1970s non lock up. It has been rebuilt and the NSS was replace with new.

The car cranks over in Neutral and Park and in any other gear will not crank.

Now there is something odd going on the 3 pins on the old switch are slightly bigger diameter. Also there appears to be 2 different NSS, I will call them short hex and long hex.

See attached photos. What's the difference in the NSS?

If I short out the loom 2 outside pins the back up lights work. The back up lights have never worked on the car since I have owned it, even when it had the old 904 lock up trans, the switch in the old trans looked quite new when I replaced it, I wonder if its been replaced with the wrong one?

Long Hex

Short Hex

Can anyone shed any light what is going on, are the parts of the switches that go into the gear boxes different lengths?

My current set up

this is my old switch I think from my lockup trans. It seems to test ok but the reverse lights did not work with it, hence it was replaced.

 

[Mikes5thAve]

When I had problems years ago both styles of switches worked in the transmission but the plug only fit the proper style of switch that went with the car.

 

[80mirada]

You may have a bad plug. Wasn't uncommon for one of the contacts to be damaged if the person installing it wasn't careful

 

[Bruceynz]

The problem is in 2 different trans the reverse lights did not work. The 2 outside pins of the NSS are not shorting together when in reverse. It seems the 2 types of switch interchange (short hex/long hex) are the switches sensetive to how far they are screwed into the trans?

 

[Bruceynz]

Just found this on a jeep forum


Short story. Recently transmission was rebuilt. NSS lasted two weeks then the jeep wouldn't start. I replaced the solenoid but that didn't fix the problem and I was getting 12 volts from the ignition switch to the solenoid. On an automatic like the TF999 the black wire from the NSS grounds the start solenoid and allows it to function. I replaced the NSS and it starts fine now. No reverse lights though. Don't know if I had them before the second switch was installed or not.
So, I removed the switch and checked continuity of the switch with it removed. Installed, there's no continuity. I bypassed the NSS at the connector coming up from the transmission and I get reverse lights. So it is the switch.....or.......whatever presses on the switch in the transmission. So what I did was remove the switch. You should have continuity with the switch out on the outer posts. The central post is the ground leading to the solenoid. On the end of the switch is a plastic piece that when depressed, sends ground to the solenoid. In the central aspect of the plastic piece is a silver bullet like switch. When pressed, it breaks continuity. This silver piece rides in a groove when the transmission is in reverse and doesn't get pressed. Otherwise, in park and all other positions, it is pressed in and reverse break lights are off. So now that I know the switch works, I started to screw it back into the transmission while it was in reverse (engine off, parking brake on, key in the on position and shifter in reverse). I checked continuity as I screwed it in every half turn until it broke the continuity. Evidently, even the slightest pressure on the silver piece will break continuity. I don't think this should happen with a new switch but it did. So, I started grinding that silver piece down ever so slightly (a thousand of an inch at a time) until I could fully screw it into the transmission, the switch be tight, and still have continuity. Plugged in the switch and the reverse lights lit up! So, if you have to replace the NSS on the tf999, and don't have reverse lights when done, it's because the silver bullet switch is being depressed and breaking continuity while in reverse. I did a search on this and there where a few posts where this was the case but no resolution to the problem https://www.jeepforum.com/forum/f8/th...witch-1070836/
Then I found this link........only after my write up. https://www.jeepforum.com/forum/f8/ne...blems-1365249/
I see we came to the same conclusion though. Evidently, there are a couple of switches out there and if you get the one with a longer central silver switch, you grind it down or take it back for a different switch. This guy got his at Oreilly, mine came from autozone.

 

[Bruceynz]

Ok looking at this I see how it works, the problem is NSS is screwed in to far, at the top you can see metal point, that's park contact,then comes down and that's reverse, everything fully depressed reverse lights on,then next metal point is netural and center pin earth's out again. I will loosen off 1/4 turn and see if that helps. Will keep you posted.

 

[Bruceynz]

Well loosing off a little and then adjusting when car in reverse didn't work.

 

[Bruceynz]

It is possible the new switch is faulty. But it's messy to get it out but that's the next step I think.

 

[Bruceynz]

Found this

 

[LSM360]

I have non working reverse lights too. My trans is a TCI 727 non lockup small block trans. "Streetfighter"

 

[LSM360]

It is possible the new switch is faulty. But it's messy to get it out but that's the next step I think.

I have forgotten, but isn't it in location such as the speedometer cable adapter so that you can jack the car (front or back) so less fluid runs out during removal?

 

[Bruceynz]

I have non working reverse lights too. My trans is a TCI 727 non lockup small block trans. "Streetfighter"

lets see if we can sort this out together

 

[LSM360]

I emailed TCI Tech support and asked them for a part number hoping they might have an answer. Next I'll pull mine and see which one I have. It's been awhile, and I can't remember which one I have in it. I know I replaced it with new one, and it didn't solve my problem.

 

[Mikes5thAve]

I wonder if it's something wrong with the shoe inside the transmission that presses the button.
You can also try disconnecting the shift linkage at the transmission and moving the lever by hand to see if it might be the linkage that's out of adjustment a bit. Make sure you've got the wheels blocked first or someone in the car on the brakes.
Other then that pull the switch and test it. Like I said on mine both swithces interchanged and worked but if there is a difference on the button side of the switch maybe some years of transmissions were more pickier then others.

 

[Bruceynz]

My issue is a 1983 trans didn't work, complete different trans from the early 1970s (one in car now) and still doesn't work, I have checked the lights work. I know the switch is not switching whether its the Chinese switch or the rooster comb is worn but if it was a major issue it would be full of people talking about worn rooster combs or Chinese switches faulty. It is unlikely 2 different trans have worn rooster comb. I know electrics good, I have multi meter hooked to switch and can see it's not switching. It must be some sort of alignment issue, I know going forward I should of checked all of this before trans was in car would of been sooooo much easier! I just thought screw in job done, in NZ we have a 6 monthly inspection, law states all lights must work on car, so I can't get my car to pass with reverse lights not working.

 

[Mr C]

I had this issue on my half ton. Jiggled the shift lever while in reverse and the lights began working. I presume you've done this.

 

[Bruceynz]

Ok got it working!! I had an old switch and it seemed to test all ok. See below I call this short hex. With a bit of trans fluid getting out, my finger in the hole I managed to swap over! Plug didn't fit now but my side cutters fixed that. We now have reverse lights!!!!

this is the culprit, brand new long hex $20 ebay special is faulty, I tested it with my meter. So there you go, mystery solved!

In the 1970s we had a prime minister like your president and he said this "ya pays ya money and ya gets what's ya pay for" old bugger was right you know!

 

[Bruceynz]

So my advice to all is check the 2 outside pins of the plug short together when you push the we center metal pin in.

There is only one switch in it, the other part just earth's the starter relay inside the trans so car can crank. Well it's kinda of a switch I guess.

Don't trust cheap switches, oh my Chinese airgap sucks air too, bitten again, found out the machining of the faces is not always parallel.

 

[Duke5A]

Make any headway on the 6.1L?

 

[volare 77]

I had two NAPA NSS fail and one was in a weeks time. I put in a NOS mopar switch 2932820 and it worked fine ever since. The China crap is junk. It looks good in the box as long as you don`t install it. LOL