I found it. F17 powers every marker light on the truck, and the VSM. That VSM is highly suspect, but you can narrow it down before spending the money on a new VSM: Pull all of your park and clearance lamps out of the sockets (including the license plate lamp), or pull the connectors - then turn on your headlamps. If the fuse holds, then you have a shorted lamp. If not, that VSM is very likely the problem, but that's not to say you don't have a chaffed or shorted wire someplace. I found the information in the wiring diagram on a 2002.

 

If it powers every marker light I find it odd that it is only the running lights that have failed.

My brake and signal lights still work on the entire truck.

In any case, after class I will do that and see what happens. Need to go get some more fuses first though.

As an aside, the tail lights are led.

 

Before you spend any more money, check your ground cables. 12VDC is rarely enough current to short circuit through water, HOWEVER, water is most definitely able to throw enough gunk into a loose ground to cause issues. Start with your battery ground cables at the frame. Take them off and clean them up with a wire brush. I bet this helps a few things, but maybe not all. The ones that don't come back right away might need their individual ground cables checked, cleaned, or replaced. Any corrosion you find will certainly cause you headaches.

With a 12VDC system, all grounds for many different systems are essentially connected together. If your ground for part A can't connect to the battery directly, it might try to connect by "taking the long way" around the frame to another grounding point. Example would be your radio actually grounding through the radiator strap instead of the battery lead due to loose connection(s). The power has to get back to the negative battery terminal somehow, and it will find a way. Electricity will use whatever route it can find, including through the body of accessories or any of those direct wired accessories you might have. If a ground can't be found at all, the component won't work. When this kind of stuff happens, you will get electricity that bypasses switches, and/or components that will come on only when something else is on.

Long story short, I've been here before. Weirdest electrical gremlin is a bad ground. I've been replacing components and testing others. Same conditions would cause a huge headache for me with the new parts. Many dollars later, I found a loose ground bolt on the frame, a dirty connection from arcing. Cleaned them up and all was well again.

 

Oh I'm with you there. I've checked all the grounds I can find. I'm sure there are some I've missed though.

I've done the batteries. A few grounds attached to the fender and the one on the frame near the tail lights by where the spare tire goes.

I found one yesterday under the dash hiding that I'll clean up when I get a chance.

 

Hm... Now I can't seem to get the fuse to blow and I haven't done a thing yet.

This is a real odd one...

Never mind there it goes. It appears to have nothing to do with the highbeams. It just takes a few minutes to get hot enough to blow the fuse.

 

I think I recall some kind of malfunction that occurs with LED tail lights. I could be mistaken... you might try a search.

 

So far I have found a random 2 foot section of red 14ga wire attached to the minor wire at the plug for the tail lights. The other end was exposed with 1/4" of copper sticking out of the insulation and just jammed inside the housing in the box. If that was my problem (so far the fuse seems to hold) I don't know how I owned this truck For 2 1/2 years and this only became an issue now...

Oh the dumb wiring people do... Blows my mind.

It must have been wired like that for a topper and the person just cut it and left it instead of remove it completely.

Doesn't hold out much hope for me for my other wiring issues.

 

Now, on to my 4lo issue.

I want to test the brake switch wire and the neutral safety at the 4wd module.

What am I testing for for each of those? Are they grounded with the brake depressed/truck in neutral or do they give 12v?

And I'm fairly certain my trailer brakes have a bad ground. Is there a ground specific to my trailer brake system?

My trailer brakes do all kinds of fun this when they are plugged in to a trailer.

 

I was just studying the 4wd system posted by tugly on page 1. If I'm reading that right, the BPP sw should give a 12v signal to the 4wd module. So I think that question is answered.

I'm a little confused on the neu saf. switch though. It shows neutral sensor wire going from the 4wd module directly to the DTR sensor. That's all fine but the way it shows the reverse wire it makes me think they all conplete a circuit with reverse. I don't get what's with the reverse wire going from the DTR sensor and branching to both the transfer case assy and the 4wd module.

One other thing is the ABS module which I would like to check, but I don't know how to. Wouldn't surprise me if there was something wrong there because I get the ABS light coming on and going off at random times.

The VSS out of the ABS module goes in to the VSS in on the 4wd module. What is that signal? a ground? and since we are on the topic. Where is the abs module. I haven't been able to find mine.

EDIT:

I know I've just asked a lot of questions, but if I had even a couple answers it would be of great benefit to me.

 

Ok 4wd stuff. All items were checked at the 4wd module plug unless otherwise specified.

Reverse light gives no signal
IGN (start/run) gives 12v
ISO BUS gives 3-4v or so at all times. I assume this is intended

Ground, functioning properly

B+ wire gives 12v constant
VSS in gives 10-11v when truck is not moving. Seems a little low but should still be within parameters met in the 4wd module.
B+ 12v constant
IGN (run/acc) forgot to check. Should be Ok.

Neutral sens gives no signal
Switch works so wires also check out
Esof solenoid works and has proper 12v to LT blue/pnk wire
4wd indicators work when shift motors shifts into appropriate gear
Lo to hi shifts motor when it is grounded
Hi to lo shifts motor when it is grounded
Bpp sw gives 12v when brake is depressed

Motors 2-5 work when lo to hi and hi to lo are jumpered/grounded so they check out.

Basically I've narrowed it down to either the range sensor/neutral sensor wire/reverse wire or the module itself.

 

Reverse. Won't shift into 4hi if in reverse. I assume that means it functions.

I'll just have to check continuity through the wire from the date sensor to the 4wd module. If that checks out I think I'll need a new module.

This sound like I'm on the right track?

 

I may be WAAAAAAYYYYYY off base here, but some of these issues sound like a bad Transmission Position Sensor on the driver's side of the tranny itself. On eBay, a used one can be had for about $15.

 

Could be. I'm going to run a jumper wire from the range sensor neutral safety to the 4wd module. See if it will shift. I didn't get any continuity when I tested it but it was kinda ghetto rigged. The connections might have been crappy to begin with for the test.

 

my suggestion was going to be to Check the rear trailer plug for bare wires.

Also i read that you have problems when it rains.

There is a write up here somewhere on leaky windshields.. some windshields tend to leak just above the fuse box and drip water on to the back side of the box it's self. over time, the water cause's corrosion on the wires inside the fuse box it's self.

there are posts about trucks doing some crazy things like starting on there own and massive electrical gremlins like light's not working exc.

some people could not see any water stain's on the box, but after taking it apart they found corrosion on the wires just behind where the fuse's connect..
Its worth a look...

EDIT... FOUND one of the post's for ya
check this post out.. scroll down to reply #9 that's where it gets good..
https://www.ford-trucks.com/forums/8...l-gremlin.html

 

I did find out my 4lo issue. Ran a jumper wire from the range sensor to the 4wd module and now 4lo works.

So somewhere along the line that wire is broken. I'm tempted to just run a new wire. We'll see. I'd rather find the break but that might be tough to track down.

As for my other problems. That's entirely possible. I'll have a look at that thread right now