NV4500 reverse lights

[1967KaiserM715]

Have an issue on my truck, 1985 GMC K1500, I put a NV4500 in from a 1995 GMC, reverse lights have been working fine for a while, but last 2 or 3 months I noticed they seemed to have stopped working. I check for voltage at rear bulbs(transmission in reverse, and ignition on.) Had nothing, so I disconnected at switch on transmission. Jumping pigtail allowed voltage and gave me lights. I assumed a bad switch, so I got a new one and tested before install. It worked fine uninstalled. But still nothing when in the reverse gear when new switch was installed. I'm not too familiar with how the switch and reverse gear work together.

What should I look for? (I can hold the shift lever all the way over and down and still no lights, so it seems like no switch contact at all.) Thanks.

[mongocanfly]

As the shift rod moves forward and back, there is a notch on the rod that the button rides in..when you go into reverse the notch moves past the switch so that the button is pressed in..if you replaced the switch did the old gasket come off?..I had a similar issue with mine..went thru several switches...then figured out my pigtail plug was bad..

[SunSoaked]

Mongo,

I just swapped a 400 for a 4500 this weekend. Where did you get the pigtail for the B/U lights? Is it a common GM part?

[1967KaiserM715]

Originally Posted by mongocanfly

As the shift rod moves forward and back, there is a notch on the rod that the button rides in..when you go into reverse the notch moves past the switch so that the button is pressed in..if you replaced the switch did the old gasket come off?..I had a similar issue with mine..went thru several switches...then figured out my pigtail plug was bad..

I hand tested the switch before I put it in, plugged the harness in and depressed the switch. Lights worked. I used permatex thread sealnt on install, old gasket came off and was ripped. I guess it's still possible the harness could have a wire break. But I'm wondering if for some reason the shift rail has a groove in it now? It looked fine when I rebuilt the transmission 2 years ago, have a good 20,000 miles on it now. And it goes in and out of gear fine. I dont know if there are other issues that can cause the rail to shift, but not depress the switch?

[1967KaiserM715]

Originally Posted by SunSoaked

Mongo,

I just swapped a 400 for a 4500 this weekend. Where did you get the pigtail for the B/U lights? Is it a common GM part?

The newer style reverse switch uses a Male 2 wire Weatherpack connector. If your get the early style SM465(pre 83 I think) you can just use 2 female space connectors.

Alot of places sell the wired 2 wire weatherpack for a lot cheaper then the GM part. Or if you have the crimp tool,also get sold as unassembled. I like to do a lot of my own wiring so I've gotten 10 packs for as much as a single wired connector before.

[SunSoaked]

Originally Posted by 1967KaiserM715

The newer style reverse switch uses a Male 2 wire Weatherpack connector. If your get the early style SM465(pre 83 I think) you can just use 2 female space connectors.

Alot of places sell the wired 2 wire weatherpack for a lot cheaper then the GM part. Or if you have the crimp tool,also get sold as unassembled. I like to do a lot of my own wiring so I've gotten 10 packs for as much as a single wired connector before.

Thanks. I didn't realize it was a weatherpack connector. I'll probably break down and buy a kit as well. I could use it in other places.

[mongocanfly]

I got my pigtail at gm..they're made of gold I think..
According to oreillys the sm465 and nv4500 use the same switch.
I tested mine to...but when I put it in it wouldnt work...so I put the truck in reverse with he switch on , and started wiggling wires...that's how I found my issue...

[AussieinNC]

Suggestion...

Have the trans in Neutral and use a depth gauge to measure from outside of the case down thru the switch mount hole to the reverse shift rail...write down the measurement....

Now put the trans in reverse and check the depth measurement again...it should be greater....

If its the same measurement, sorry its bad news...you may have the shift shaft itself in 180 degrees out of phase, placing the reverse detent on wrong side of shaft to allow switch to operate....

The shaft will still operate,,,the detent ball and spring will compress enough for shaft to operate.

It doesnt happen very often, but I have seen it about five times over the years...