Neutral Safety Switch

[7212Mopar]

I have an 904 automatic trans that was professionally rebuilt with zero miles and had been battling with the neutral safety switch to make it work the last few days. At first, I could not get engine cranking and no reverse light. Thanks for the advise from a member here, I got engine cranking in P and in N, but no reverse light. I tried a number of NSS, different gasket thickness, no gasket etc and could not get it to work probably with both engine cranking and reverse light working. I finally got it resolved tonight and typing this up so someone else facing the same issue as me for the first time might have an easier time.

From a lot of reading here, CC and the web, for the three pins NSS, the center pin is internally grounded. When the metal part of the plunger touches the P and N positions of the rooster comb inside the trans, it forms the ground to the starter relay to allow the starter to crank over. The left and right pins complete the power circuit to the reverse light. When the metal pin of the plunger is released, the circuit is made and when the pin is depressed, it opens the circuit. The rooster comb inside the trans has a plastic insulator that leaves the P and N positions metal part exposed, allowing the pin of the switch to make contact to make the ground. The insulator at the reverse position has a recess slot to allow the metal pin of the NSS to extend fully completing the power circuit. The metal pin can go up and down with the white plastic plunger and also independently. The white plastic plunger is merely for position the switch against the rooster comb and provide a little force so that the switch rides along the insulator part.

I gone through three brand new NSS for my lesson (first time). Switch one was purchased from CI. Switch two was purchased from YO and third switch from a local NAPA Auto. All three were made slightly different. Switch one and switch three are almost identical except the hex part of the body. Switch one is slightly shorter and is cad plated. Switch three is yellow zinc finished . Switch two is also cad plated. Switch one and three has a longer pins and switch two has a very short pin, about half as long. The picture shows switch one on the left with switch two on the right. I grind down the white plastic on switch two as part of my trail and error so the pins appears longer than originally. As you can see, the thread counts varies a little and the shoulder where the gasket goes is different. Switch two can get deeper into the trans.

I got switch three working tonight after I drop the pan and look inside the transmission. Rooster comb positions were spot on with the NSS but only engine cranking and no reverse light. The pin at the reverse position was extended almost fully but may be just a hair shy for the internal of the switch to fully release to form the circuit. Instead of modifying the NSS further, I use a Dremel bit to shave off more plastic from the rooster comb insulator at the reverse position. The final picture after the modification shows a very small gap between the pin and the insulator. Also note how much the white plastic plunger is depressed. Check your new NSS with your old one and test the switch first before installing as it might save you some pain. Sorry for the long post. Hope this help others.

[RUNCHARGER]

Great photos and explanation! I'm sure this will help others, glad you got it working.

[Cuda Cody]

   Nicely done.  Thanks for sharing.   

[Dakota]

Sorry for the long post. Hope this help others.

Absolutely no need for "sorry" - the detail is terrific as it helps others understand what you tried and eventually succeeded in doing.   Thanks for taking the time to write it all out.

[Poacher]

Ok,nube here but I'm glad I found this site. I have 72 Cuda with 727(don't know the yr yet have not pulled pan) but my reverse light are on thru drive gears. I pulled NSS sensor 3pin and looked inside there is no rooster comb plastic part and the comb looks different than my complete 1978 727 I have it's rooster comb w/plastic part in there. I assume this is a 1967 or earlier 727. How do I install a one wire NSS sensor that will allow my reverse lights to turn off. I'm not for sure how they grounded the R-lights so they work correctly. I was also thinkin' can I removed the 1978 valve body and put it in the 60's? transmission so that I will have the proper Rooster comb plastic parts. Will that work?  Thks for any help

[dodj]

Sorry for the long post. Hope this help others.

Posts like this are what make the site great. There are, I think, very few people who even know about that rooster comb and how it works. Now there will be a lot more that understand how their NSS works.
Great job!!

PS..There was once a member on cc.c called Tactransman that posted up pics like that to explain the rooster comb. It was only after his posts that I really knew how the system worked.

[7212Mopar]

Ok,nube here but I'm glad I found this site. I have 72 Cuda with 727(don't know the yr yet have not pulled pan) but my reverse light are on thru drive gears. I pulled NSS sensor 3pin and looked inside there is no rooster comb plastic part and the comb looks different than my complete 1978 727 I have it's rooster comb w/plastic part in there. I assume this is a 1967 or earlier 727. How do I install a one wire NSS sensor that will allow my reverse lights to turn off. I'm not for sure how they grounded the R-lights so they work correctly. I was also thinkin' can I removed the 1978 valve body and put it in the 60's? transmission so that I will have the proper Rooster comb plastic parts. Will that work?  Thks for any help

I just responded to your PM. I am not familiar with the one wire NSS. As far as the various years on the trans, try reaching out to A and A Transmission or Cope Racing transmission. Both vendors are great to deal with.

[Bullitt-]

  seems '69 is the break point for a single wire switch according to these guys. last post in this thread says the reverse lights were not from this switch.
https://www.forcbodiesonly.com/mopar-forum/threads/1966-727-neutral-safety-switch-replacement.79532/

[Poacher]

Anybody tell me how to fix my 727 NSS issue. I pulled the switch and when I looked inside there is no plastic rooster comb part so that's why my reverse lights are not turning off while in drive 2nd & 1st gear. I have not pulled the pan but I'm thinkin' it's a pre 1968 727 tranny. How can I make this work and turn my R-lights off. Can I find a single wire NSS and some how ground it some how so my R-lights will turn off? or can I take the rooster comb plastic part from my extra 1978 727 transmission and put it in the pre-68' tranny then will the R-lights turn off? If it will fit? Thks