1985 F150 won't start, no power to lights, etc
 

So a followup to a previous post where I thought the issue was linked to an attempt at wiring a new ignition switch: my truck, a 1985 F150 4.9L 4x4 manual with the T19 trans, won't get power past the ignition switch to the headlights, marker lights, etc, and won't even try to turn over when the start circuit is completed. Just until the other day this was working fine, and after trying to wire the switch it stopped working. I metered everything out and it was getting voltage to the ignition switch as intended, but still no start. So then to be sure, I wired it all back the way it was originally, but still nothing. At the ignition coil there is 12V, and when jumping the starter solenoid the truck will turn over and spark, However, when I turn the key, nothing. Again, I metered it out and every wire at the ignition switch has 12V, so something must have created an open circuit.

And upon further inspection I had strengthened that theory when I found this jumper wire on the ground under the truck:
https://cimg0.ibsrv.net/gimg/www.f15...92b3659f6a.jpg

It was found underneath the truck, however there is a possibility it fell through the floor of the truck, as the transmission tunnel was cut out and replaced, but the P.O. did not weld it in but just bolted it in a few places causing a gap around the edges. (That'll get fixed don't worry)

Any ideas of where this could go and if it could be the cause of the problem? What circuit could this wire go to that causes everything to lose power (if this is the cause at all)? It is a pretty beefy wire, if that gives anyone a clue as to what it was used for. Thanks in advance!

EDIT:

Upon metering out the headlights, the driver side headlight is grounded on all three wires, where the passenger side is not. Since they should be directly connected something seems messed up with that. Since the driver side headlight plug is grounded on all three pins there must be a short circuit to ground. Would a short circuit cause this issue?

Lol, that's electrical wire for housing, not for vehicles. Whatever the wire went to, you can rest assured that it was a hack job. That's not too unexpected on an older vehicle. We used to use wires, paperclips, or even nails to jump power between places on the fuse box.

My suggestion is to examine the fuse box and make sure everything is like it came from the factory, including checking the fuses to see if they're blown. If the box is melted, charred, taped-up, not mounted, etc, these are indicators that something went wrong and the owner bypassed some stuff to get it working again. My 1985 has all these problems. You can find fuse box diagrams on the internet if the fuse box cover is missing. Next, trace the wires from the battery. The negative side should go to the engine block or somewhere on the frame. The positive side should go to the starter solenoid and then to the starter. There's usually a jumper that goes between the starter solenoid and a distribution block to share power to multiple locations, one of which should be the fuse box by way of the ignition switch. You turn the switch on and the fuse box receives power too.

Good luck!

You are probably right there, the fuse box is kind of just...dangling... I checked the fuses that are on there and none were blown, but I'll have to look up the fuse diagram because the cover is missing like you said. And thanks for the info, I'll check to make sure the fuse box is getting the proper voltage after work today, thank you!

Click this, read the caption, & follow the links in the caption:

https://www.supermotors.net/getfile/...rwiringold.jpg
(phone app link)

This is close (or identical) to your fuses:

https://www.supermotors.net/getfile/...useblock86.jpg
(phone app link)

But you should invest in a Haynes manual:

https://www.supermotors.net/getfile/...l/hayneses.jpg
(phone app link)

Thank you! That will come in very handy, I appreciate it. I have a Hayne's manual that's been helping me figure out this wiring but that doesn't get too detailed with the ignition switch unfortunately, so these ought to help immensely. The manual has helped with straightening out a lot of this wiring situation so far though, it was (and still is for the most part) a mess. Hopefully I'll be able to undo all the jumper wires and splices the P.O. made and at least keep some of these wires separated like they're meant to be.

After getting back from work I metered out the fuse box, checking voltage on every fuse. Some had the 12V and some had almost none, maxing at around 300mV for others. All of the fuses linked directly to the ignition switch are fine, and get 12V, the ones that don't are powered through other switches, such as the headlight switch. I tried testing them with the headlight switch on and off, but no change in results. To be exact, using the numbering system from Steve's " '86 Fuse Block Diagram" : Fuses #4, 5, 8, 9, 16, 17, and the turn signal flasher all had between 0-300mV. I don't have any clue if this is normal when the car is set to 'RUN'. The power window and doors circuit breakers are not present on this truck. I'm going to go back and start checking the potential between every wire going to and from the other switches in every position right now and see how they are acting.

If the switches being off are causing no voltage at the fuses, and that's normal, what could be wrong? And if that is abnormal, why would the fuses connected to switches be causing a no-start condition? Thanks in advance!

Update 2.0 - Headlights are now working. After testing the wires at the headlight switch I noticed the Blk/Org wire that is supposed to supply the 12V was not doing that, so I checked the alternator regulator wires and noticed a broken splice, and after testing for continuity - BINGO

But apparently that issue was 100% separate and the truck still won't try turning over. I'm going to now test continuity between the starter solenoid wires and the ignition switch. Any other ideas? Thanks!

Update 3.0 - Wiring is fixed! Although it seemingly arose due to me wiring the ignition switch, it appears that 2 independent issues arose coincidentally at that exact time. On the starter solenoid, the start wire had corroded at the connector. It was hidden under the insulation, however the wire had gotten bad enough to break free, leaving a spot along the wire that was looser than wire should be, I noticed it when checking continuity between the starter wire and noticed there was no longer any. Very strange that this all happened at once, talk about bad luck.

Yep: coincidental failures are frustrating & confusing. Good job pinpointing them both so quickly.

But you should still read the caption of that Haynes manual pic - it sounds like you have the wrong (newest) edition for your truck. A red-cover would serve you better than the newest blue-cover.

Yeah I think that's probably the case. My copy of the blue cover edition has nearly reached the end of its life and the binding is next to nonexistent anymore, so I think I will invest in that earlier version, thanks for the suggestion