I really hesitated to post this but ive wasted enough time on this. 77 f150 4x4.
4spd trans. 3g alternator upgrade. I replaced the clutch and the reverse lights quit working shortly after. Pulled the plug off the trans, tested the switch for continuity when shifter is in reverse-failed. Jumped the terminals of the reverse light plug, all wiring passes continuity tests. The fuse is good, power to both sides of it, i have power to the back of the fuse box. The washer pump works which is on the same fuse as the backup lights. I have key on power to the accessory plug (?) behind the dash that looks like a flat trailer plug at the black/red stripe wire (backup light wire color). I have no power at the black/red stripe wire going out to under hood. I can put power to either spade terminal under the hood and get the backup lights on.
Ive searched the schematics and it doesnt show backup light power going anywhere other then the lights but there is a junction under the dash somewhere. Im about to cut the shrouding off the wiring under the dash but i honestly cant believe its bad in there. Every other electrical component works fine.
I hope someone on here can help me out, this has been the most frusterating wiring problem ive had on a dent yet

 

<TABLE id=post9504897 class=tborder border=0 cellSpacing=1 cellPadding=6 width="100%" align=center><TBODY><TR><TD style="PADDING-BOTTOM: 0px; PADDING-LEFT: 0px; PADDING-RIGHT: 0px; PADDING-TOP: 0px" class=alt2><TABLE border=0 cellSpacing=6 cellPadding=0 width="100%"><TBODY><TR><TD noWrap>******** type=text/javascript> vbmenu_register("postmenu_9504897", true); *********>
Moderator

</TD><TD width="100%"></TD><TD vAlign=top noWrap>Join Date: Jan 2006
Location: Waterloo IL
Posts: 1,706




</TD></TR></TBODY></TABLE><!-- / user info --></TD></TR><TR><TD id=td_post_9504897 class=alt1><!-- message, attachments, sig --><!-- message -->The connector I'm holding with my finger goes down to the back up light switch on the transmission. There is some extra wiring there but you can see it goes into the harness that comes out of the firewall. Just start at the firewall and come out about 8 inches or so and you should find it.
The connector I'm holding is really odd as well. The transmission side is sort of like a 90 degree male spade clip. Unfortunately I'm at work right now so I dont have the colors of the wires handy. Hopefully this helps.



<!-- / message --><!-- sig -->__________________



</TD></TR></TBODY></TABLE>

 

I might be mistaken but I swear that's the NSS plug.

 

Ive tested all the wiring to that plug, continuity checks out good, i can put 12v to either one of the spade terminals there and get the backup lights on. My issue is before that plug. The backup light wiring must split off after the fuse box. My issue is between the fuse box and the firewall plug i think

 

1973/79 F100/350 Warner T-18/T-19 & NP435 4 M/T backup lamp switch (15520 in pic) threads into the shift tower.

With A/T, the backup lamps are controlled thru the NSS. 1967/77: NSS located on steering column; 1978/79: NSS located on transmission.

 

Thanks for the info number dummy im working with a np 435 but in my first post i said i tested the switch which failed but since its a normally open switch i just jumped the 2 wires together to mimic a closed position (shifter in reverse) . I can make the lights work by powering up the circuit from the engine compartment. Confirmed that the black/red stripe wire has no voltage coming out of the firewall plug, that only leaves the wire from after the fuse box to the firewall on the interior side. Im still having a hard time believing there is a broken wire though

 

Well i got it "fixed". Said screw it and pulled power from the trailer plug looking thing under the dash and hooked it up, capped off the old "dead" black/red wire that has lost its connection, and ran a new wire to the original black/red wire about 2" ahead of the body plug and spliced together. All is well. May not be 100% correct but its still protected by the #11 fuse like normal plus this is just a pos beater but i hate when things dont work as they should!

 

HIO Silver....yes and it is tied into the back up lights, according to mikeo0o0o0...

"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. 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. Here's the little jumper in the engine compartment.
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."