Yesterday evening, moving the '77 from the back yard out to the drive before the rains and snow today, it was dark and as I backed up, I noticed I had no back up lights at all. Was checking them, noticed the front marker bulbs were not lit with other lights either. Spent an hour plus trying to find in charts where they are related, they aren't. Went back to check again, found if I put just a little pressure on the front side marker light bulb holders while they are on, they light up. I guess the housing supplies the squeeze when bulb in holder is twisted into place.
One fix.
Those back up lights, I'll catch a warmer (i.e.: not a 27 degree and dropping windy like) day to track it down. I tried messing with the NSS, reaching underneath the dash and manually moving it while truck run in neutral. No dice. Fuses all good too. In one book it references a fuse link in a wire behind the left side of dash in the engine compartment. Maybe I just traced wrong lines in the book? This was sudden.

 

I think those 194 marker light sockets should grip the bulb contact blade as tightly out of the lens, as when it's engaged in the lens.
You can try running a small file (like a nail file) against the contacts, and then using a small prying implement to try to bend the contacts meaningfully, in a manner which leaves them gripping the bulb tightly, creating good electrical contact. Another available trick is pulling the contact wire loops away from the glass of the contact blade. If necessary, you can put something between the wire and the glass, to shim the wire outward, in the interest of a better contact.

Backup lights, I'd probably check for power at the sockets, and work my way forward till I found power - but it might make more sense to start at the switch and work backward.

 

At least the front lights got fixed. For the backup lights, you already did ck the movement of the NSS by hand to see if they came on. Of course did you check the bulbs themselves? Then fuse #11 (back u lights and w/s washer)? Here is some talk about the NSS and the back lights, maybe in here is some help?

"When the trucks came with a manual trans, there was a dummy plug used to bypass the NSS switch. I've never been able to come up with a part number for the dummy plug. To bypass the automatic set up: Unplug the switch and discard or ignore. There are four wires in the harness plug, two each, red w/ blue trace and black w/ red trace. Run a jumper between the red/blue and red/blue, do the same for the black/red. That completely bypasses the NSS switch. Your truck will now start and the back-up lights will be permanently on. Now on to the backup lights.

In the engine compartment is a little U shaped jumper wire. It'll be located on the drivers side splash pan, just in front of the firewall where the wiring harness comes through. Unplug the little jumper, this will shut off the back up lights. (4 spd) There should be a back up light switch on the trans cover. Run two wires from the switch to the two wires that were jumped. This will get your back up lights working again. Just a note, you could make a jumper plug out of the NSS. Cut the switch off the harness and splice the two pairs of wires. I just hate to cut these switches up. New, they're getting pricey. EDIT: If you don't care about the back up lights, just jumper the red w/ blue trace wires. This will by pass the NSS but the back up lights won't work."

 

I WOULD NOT BYPASS THE NSS SIDE OF THE SWITCH!

I would pull the fuse and check it with a meter not just look at it and call it good.
Sometime the fuse holders get a film on them and cleaning the fuse & holder it will start working.
I would also start out back to see if there is power at the sockets and work forward.
Dave ----

 

No, I am not gonna :"bypass" the NSS, I like the "automatic come on in reverse" function. I might would wire in a hidden, tagged (for future ID) toggle switch parallel to the NSS for back up lights, as I've already done for the start side ... but I'll fix the automatic on function too.
What threw me was after backing up and seeing NO backup lights which have always worked, getting out and finding front marker lights out too. I simply could not find a common denominator other than they were all 4 on the same truck. After thinking about those rubbery marker light sockets, I figured them out, was a huge leap there.
Guess I'll just wait for better weather now.

 

Oh NO I was NOT suggestion to bypass the NSS at all. I just included all the saved text from a fellow FTE member. Yes ck that power is getting to the correct places.

 

I wonder if you have a ground connection somewhere going bad, and the result is that the backup lamps and marker light malfunctions actually are correlated.

You squeezed both front marker light sockets and caused the bulbs to come on that way? Look past the sockets for a few minutes, and turn on the lights and reach up under the front of the truck (or from under the hood) and do a wiggle test on the harness which supplies the marker lights. Maybe there is a problem 'downstream' from the sockets, far enough down to affect both lights, and merely handling the socket ends is enough to jiggle the harness several inches away, toggling the bad connection. Did you verify that only the one side was lighting up when you squeezed the socket?

 

Thank you for the suggestions though. Truck has been out back near my basement's enclosed "trike room" big double doors, I was just moving it so no predicted snow would fall off the metal roof from some 15-20 feet above onto it ... and to get it out of the yard before it got so wet and mushy. I had been doing my front fenders, and I just need to check for power at the sockets next. As I read the schematics, BU lights ground with the taillights.

 

I pulled the truck around to my "work area" outside those big doors determined to find the fault. I pulled the lights out, removed bulb holders for back up bulbs, pulled the bulbs that are pretty new, I checked bulbs, both work. I checked my sockets ground contact, they are grounded. I rigged a set of jumpers so I could clip one on the hot terminal, and another to a ground as two do not fit in a bulb socket. I hooked up a test light, nothing as I pulled the gear lever through reverse with key on. I checked my test lights, they both work off the battery perfect.

I checked all my fuses, they are good.

I wormed my way under the dash to inspect the NSS, found a mess of wires added in last 45 years and a switch I could not recall. I traced it to a relay under the hood over near the battery, thought must have been for old fog lights, so I removed the wire and that switch, then was pulling the relay when I realized what it was. It was a switched relay for running power only to a trailer's running lights. I rewired my booboo, solder, shrink, etc. I then neatened up the other wiring, clipped a few zip ties, and then I could see to the NSS. I looked over the wires running from the start wires (sort of red with blue tracers) over to a emergency bypass switch I put in a few years ago, and tomorrow I'm gonna drop the switch to inspect contacts. It started getting too dark. I can see where the two reverse (black with red tracers) wires attach, I can probe it from below I think.

I'm suspecting the switch, maybe contacts loose or dirty. The tab is there too. I did run my hand up the wire group to see how far to the flat 4 pin plug, but it went through a hole before I found C-1015.

But I did get my trailer running light lead fixed where I messed it up, also marked it ... and I also inspected all my harness under the truck for rodent damage.

 

Well, I got back up lights now.

Spent the day working on it, crawling, opening up harness after pulling, inspecting the NSS. NSS works perfectly, it was a hair out of adjustment. To adjust it I put a very small allen wrench in that hole with the switch tab pushed against the spring. My books told me was neutral, but on my '77 it was park on the lever. Shift lever in neutral and the tang was a long ways from the tab. When placed where it was, it was close, so I adjusted it so the plastic tab was against the tang sticking out the collumn, tightened the bolts there, pulled the allen wrench out, then tried it out. I's better aligned than I ever recall it, no more pushing up in park or neutral to start, just put it in neutral or park, and once I rigged a light, I found reverse was perfect in reverse position, but still no BU lights. After many harnes checks, the break is beside the gas tank someplace, so I spliced in a bypass from the rear plug to just over the rear axle, lots of soldering looking up, tape, shrink tube over tape, rewrapping harness sections etc.

But they work.