Reverse Lights only work with Neutral saftey switch is out of the tranny

[idrivemopar]

A bit puzzled as my reverse lights only work when I remove the neutral safety switch from my 727 transmission. I tested with two new switches and same result. When its installed in the car and hooked up, the neutral safety part works, but no reverse lights. I'm beginning to wonder if the tranny shop overlooked something here.

Any thoughts?

 

[68GTX440]

Do you have a single wire or 3 wire switch?
Floor shift or column shift?

 

[idrivemopar]

Floor shift, 3 wire.

 

[68GTX440]

What year and model is your car?
If you have a console the reverse light switch should be in the console.
And
Your car should have a single wire switch for park/neutral only.

Is it possible that the car is wired wrong and the trans switch is also connected to the console reverse light switch? And backwards?
If memory serves me the center is your constant ground and depending on the position of the shifter it will deliver a ground to the correct circuit. ie:starter or back up lights on either side of the ground pole.

Do a continuity test between the console switch and each wire on the trans switch and see which wire feeds and what location they go on the trans switch. (Right middle left) You might be able to disconnect 1 wire from the trans switch and all will work correctly.

Floor shift, 3 wire.

 

[A383Wing]

looking at his avatar, I doubt he has a console reverse light switch

 

[68GTX440]

Good eye. I never did look at his avatar.
So if that is the car he is referring he has another problem.
Even now looking at the bottom of his post I see
"1973 Roadrunner - Nearing restoration completion!!!"

looking at his avatar, I doubt he has a console reverse light switch

- - - Updated - - -

Lets go another route.
When you say you have the switch out of the trans and it works, are you pushing in on the switch?
Can you move the shifter very slowly and see if the lights come on or flicker?
Maybe the switch is not in far enough?

The pan may have to come off and make sure the slide on the valve body lever is not broke or worn out.

 

[A383Wing]

was trans worked on? Maybe wrong lever installed inside?

 

[bigmanjbmopar]

All I can say is on my 69 RR the wires that come from the NSS are routed through the starter relay, and provide a negative (ground) connection. the third pin or wire is for the reverse lights, if you can start you car normally have you tried it in gear?

This will tell us if the trans and new switches are working together, if they are then have you checked the fuse for the lights and are you sure there is no break in the wire heading to the rear? In my car the wire gets a positive from the NSS once in reverse and sends that + 12v to the lights which are grounded in the bumper.

The wire in my car travels from the NSS into the cab on the drivers side and runs down the side to the rear trunk area were it exits through a grommet then to the lights.

You can test for voltage at the lights with the car off, just turn the key to on and meter or voltage check probe the feed + 12v wire to the lights. No voltage means a break in the wire, working backwards form there trace and find the break. If it is good all the way to the NSS than you may have the wrong one for you trans.

 

[rebootej]

I had this same problem when i swapped a 727 for the 904 that came with my 74 Satellite. Turns out the 727 was an old model and had the lever that only operated the neutral safety switch. Maybe they did forget something?

 

[idrivemopar]

It has to be something in the trans. I have moved the shifter back and forth, and no flicker, nothing, this means the switch when installed in the trans is depressed, keeping the lights off, as when its fully extended, the lights come on. I can only make it work when the switch is not installed in the trans. So, the wiring is good throughout, and it did work before I pulled the trans and had work done. Now, the neutral safety feature on the switch works, so my guess is that something on the internal switch plunger is not functioning right to allow the switch to depress and turn on the reverse lights.

 

[68GTX440]

I would talk to the shop that did your transmission and see if they did a valve body swap. As said in a previous post you might have an older valve body that only works for the NSS. Either that or there is a problem with the main shift lever inside the trans. In the previous pic I posted the red arrow shows where I am referring to. You might be able to pull the NSS out and look inside and see if it is broken or missing a step for reverse.

Here is a picture of the old style lever.


This is what you should have the newer style

 

[idrivemopar]

I have the older style, however, after inspecting the old switch and the new switch more carefully, I found the newer switch has a longer reach inside the trans, and therefore, may be the culprit never allowing the button to fully extend and turn on the reverse lights.

Here is what I mean, new one is the brass housing, and you can see its longer then the original.

 

[68GTX440]

Can you put the old one back in?
Does it leak or is it bad?

 

[idrivemopar]

Can you put the old one back in?
Does it leak or is it bad?

No, it has a broken off pin.

 

[A383Wing]

looks like your problem has been found....install correct lever inside trans or find correct switch and lights should work like they should again

 

[idrivemopar]

Not all parts are created equal!!!!!!!!!!!!!!

What an exercise in futility because not all parts are created equal.

I did find the correct switch, from Autozone, the silver one on the left. Orielly, AdvanceAuto, and NAPA all have the incorrect one(the brass color one).

Thanks cheap Chinese crap and no product oversight on quality and accuracy for 2 hours of my life I will never get back!

 

[bigmanjbmopar]

So it was switch? not lever in trans?

 

[idrivemopar]

Yep it was the switch! You can see in the photo, the brass colored one is just a bit longer then the original and the correct replacement. Because of that, the switch never can fully let the plunger out, which activates the reverse lights. So the original and silver replacement are slightly shorter and it allows it to work properly.

 

[bm02tj]

The worst part is when you find their screw up they tell you you cannot be right
I am like you I save all the old parts till I am complete and happy then only save the good spares

 

[bigmanjbmopar]

Did the lock out work? could you start it in gear?