backup lights not working

[mb70Coronet]

Hey guys...new to the site...My 70 Coronet has a 68 727. I purchased the car already restored. My reverse lights do not work in any gear. I checked the neutral safety switch...it's a 3 wire (which would be correct for the car but possibly not for the tranny). The car will not start in gear so the switch seems to be working as far as that is concerned. Does that mean the 3 wire switch is working and the lights problem is elsewhere?

 

[70BEE&500]

Not being a wise guy but you only want the reverse lights to work while in reverse. It could be the neutral safety switch itself. Here's why. There is a contact on the tip of the switch for Park/Neutral for the car to start. While in reverse gear, the plunger moves out on the switch, thus closing a circuit and turning the reverse lights on. Any other gear and the plunger is pushed in and the circuit is open. I had a brand new one bad from the get go. Somehow the plunger rotated within the housing and the contacts were misaligned and NO LIGHTS! I found this frustrating as I had just got my tranny together and full of fluids. My solution was to jack the car up with two floor jacks on drivers side. This put most of the fluid to the other side of tranny and I had a buddy plug the hole with his finger. This stopped/eleminated very little spillage. New switch and it works great. Hope this helps and it could be a wiring/ground issue but I would start with a new switch.

 

[mb70Coronet]

You're right, of course, about the when the lights should come on. I guess I was not as clear as I should have been. I have read on some other threads that if you use the wrong NSS (3 wire vs 1 wire) that the reverse lights will come on both in reverse and drive. I know that the tranny is from 68 which, depending on when it was manufactured, could have used either a 3 wire or 1 wire and the car is a 70 which is looking for a 3 wire NSS. So will a 3 wire switch work (as far as not starting in gear) in a tranny that should have had a 1 wire switch? Also, if the contacts did somehow get misaligned, would it be possible for it to still work as far as starting in gear?

Sorry to be so long. I want to make sure that I am explaining myself a little better.

 

[70BEE&500]

I'm not real familiar with 1 wire NSS's as I have 3 wire. What is the wiring harness like that plugs onto the NSS? Does it accept 3 prongs or 1? What are the wire colors? Maybe I can learn something as we go as well. Secondly, contacts? There is a single contact point on the plunger part of the NSS. This silver tipped point is what contacts the valve body arm within the tranny. When you initially set you valvebody in, it's always good to check the alignment/fitment of the valvebody to the NSS. It all has to contact in the right places and then you torque it down. The contact should only hit in two places on the valve body arm - park & neutral. This contact is the grounding point for the circuit and allows starting. The other contact is withing the plunger and you can't see it. I found that my plunger had rotated by doing a simple test with ohmmeter. The plunger should not spin/turn in the housing. The plunger should just go in/out. The contacts within are for the backup lights. Silly question, did you verify the bulbs are good? Check the wiring? Do you have a factory service manual? This manual is priceless and I always refer to it when doing something.

 

[74sundance]

If you over tighten the switch it can/will damage it and it will not work.....

Automatic trans car's have two spayed connectors on the starter relay, one go's to the Neutral safety switch (The center pin) it grounds the wire in neutral or park.Thats why if you unhook the harness to the switch it shouldn't start.If it do's start you might have a short some where.
The other two prongs on the neutral safety switch operate the backup lights.

Test Procedure:

Disconnect the wiring connector at the switch
Using a test light or volt-meter test for power at the wiring harness with the key in the "engine crank" or the gear shifter in the "reverse" position. (do not start the engine)
If power exists reconnect the neutral safety switch and probe outgoing wires at the connector.
If no outgoing power is present the switch has failed and needs to be replaced.

 

[70BEE&500]

Any luck? Put the gear selector in reverse, put an ohmmeter on the two outer pins. You should get continuity as the circuit is now (should be) closed. If not, the switch is bad. In park & neutral, center pin to frame should read continuity as well. Hope this helps.

 

[mb70Coronet]

As a matter of fact, I am working on some transmission leaks today (lunch right now). Once we took off the pan we saw that it has the wrong rooster-comb. We're going to try changing it to the correct one and see what happens. Thanks for all of the great help and information.

 

[Propwash]

How about your back up light switch? Just going off an issue my 68 had....

 

[mb70Coronet]

Well, we were not able to install the correct rooster-comb for the car because of trans build differences. We'll have to stick with the comb that is in the tranny. I did discover why the backup lights don't come on at all in any gear (which I keep reading they should be doing with the 3 prong NSS)...no bulbs! DUH! I'll have to try to figure out some way to "rig" a switch to work when car is put into reverse. More later...

 

[mb70Coronet]

Finally solved this issue (for anybody that may have something similar). Found 2-wire plug inside of engine bay for reverse lights. Jumped one set of connectors, then took a piece of electrical wire (2 wires), split it and connected one wire to one side of male plug and the other wire to other side of female plug. Ran electrical wire through firewall and connected to 12V relay from Radio Shack. Ran another wire from fuse box (radio fuse) to one wire of small, pill-sized burglar alarm contact which I mounted under steering column. The other wire from contact goes to ground. I mounted the magnet on the bottom of the gear shift collar on the column...even with contact at "R" position. When magnet lines up with contact, lights come on. When magnet moves away from contact, lights go out. Seems to be working so far...

 

[scottlanes]

does anyone have a diagram of how the switch is *supposed* to be set up at the base of the steering column?