While adding a light inside my cap I discovered that the fuse block by the driver's side kick panel is negative feed. I ended up having to run a line from the + bat terminal and the second line from the fuse tap (-).

Can someone explain the logic of this as opposed to having the fuses on the positive side?

 

Uh, no its not.

 

How is it then that I have a one wire from the positive battery cable (actually spliced into the red cable 2 inches from the (+) post and one wire from the cab fuse block, center fuse (I think #15) and those 2 wire connected to the 2 wires from migh new light, make light. I am accessing the fuse power by using a fuse tap, It plugs into the fuse slot and has 2 of its own slots, 1 for the original accessory fuse and one for the new accessory.

 

http://www.buildabox.net/99fusebox.htm

there is the fuse box. If you have the thing grounded at fuse 15 then its gonna have power on that wire with the key on, and of course it will show a ground with the key off. You do know that a fuse that is connected to a load, and is not being supplied by power will read a ground on it through the load. But whether or not you are getting a ground off a fuse in that box, Whenever or whatever powers that circuit up will turn your new litttle light off, since there will be power on both sides.

Check again and tell me exactly what fuse you have it in, and i will tell you what to do or what to turn on to show you that your new light will go out.

 

OK, here's is all the poop I have. For background and at the risk of drawing abuse, I am an Electrical Engineer in AC power circuits. Everything I am about to describe here has been verified by another EE that I work with.

I am using a fuse tap which I described previously, It connects into the fuse slot. I have it plugged into slot 18 in the cab fuse panel. The wire from this tap runs back to my fiberglass cap where I have a light with 2 wires. The light is otherwise entirely isolated from the frame. The other wire from the light runs back to the battery red wire going to the + terminal and is spliced in there. The light has a pushbutton switch built into it. Wired as described here, the light works normally regardless of whether the ignition is on or not. Works without key in ignition.

Originally I spliced into the negative battery wire to run to the light while using the fuse tap for what I thought was +. This would not work key on or not didn't matter. I did not change the fuse tap wiring but just switched from the battery neg wire to pos wire and voila. I now have a light on in the cap. So it works fine, I am just curious as to why I am getting a negative in the fuse block.

This is very simple wiring, frankly we see no other answer than a negative fed fuse block. Again one wire from pos batteryat battery. One wire from fuse tap. One working light, no other metalic connections.

 

Well im not a EE, but i did help a EE friend of mine with his college work, and he still calls me from his job from time to time.

Let me get out the guns. I dont post answers on here unless i can back myself up with proof.

Ok, here is where you are wrong. Look at this diagram
http://www.buildabox.net/fuse18.htm

Ok, you are hooked to fuse 18, so as long as the headlight switch is off, then you are getting a ground through the filaments of all of your parking lamps. You see, when you have a load connected to a circuit that is not being powered, then you will read a path to ground through the power side of the circuit, minus the resistance of the load. Look at the fuse 18 in the top right of the first diagram. Follow circuit 14 over to splice 224, then notice that that goes to all your parking lamps, therefore allowing your new camper light to ground through them (although not at full brightness due to the resistance of the filaments). Now look at the other wire from that splice to where it goes to point M. Look at the bottom diagram to see where point M picks up. That wire is connected to the park and head terminals inside the headlight switch, which is fed by the always powered fuse#6. Ok, now the purpose of the fuse#18 that you have tapped into's pupose is to carry POWER, not ground, to circuit 1045, through point L to point L on the second diagram, to the GEM module trigger and to POWER up the internal pulse width modulated instrument cluster bulb dimmer.

So now, tell me another fuse in that truck is on the ground side and i will show you why it's not.

BTW, turn your new camper shell light on and then turn the parking lights on. What happened to your ground???

 

Aha!

So, the park lamp relay connects junction 224 to the + side of the battery. Regardless, I understand now.

However, the light is not dim ti is quite bright. Prolly because there are several lamps paralleled to gnd yielding a very low resistance. Anyway, the cap light does go off when the parking lamps get turned on. So looks like I need to move the tap to a different fuse, maybe the cig lighter, and then move the battery connection from + to - which would be better anyway.

Thanks, now I'll be able to sleep at night, there is balance in the universe.

 

Actually, its opposite, the splice 224 connects power to the parklamp relay (thats just for the trailer parking lamps). The fuse#6 in the bottom diagram connects the power to splice 224 when the headlamp switch is turned on, therefore lighting the parking lamps, turning on the trailer parking lamp relay, and supplying power to the fuse#18 that supplies power to the PWMdimmer module.

Anyhow, what i would do is not use that fuse tap thingy and since your wire is right there, pull off the kick panel cover and ground that wire to a 8mm bolt that you should see with the kick panel off.

Hope i explained all that without seeming like a a-hole, but ford truck wiring is what i do for a living and i can guarantee you that they havent ever fused a ground side of a load, because while it would still protect the load, it wouldnt protect the wiring from a short to the body.

 

Good point, I already mounted a toggle to the kick panel and ended up buying a separate inline fuse that I installed at the battery because as you already pointed out when I thought I needed a + wire from the battery, I then needed a fuse at the bat to protect that line from damage and grounding to the chassis.
Thanks