Ok, so I'm mostly posting this as a question to Bob Rwenzing, but I figured everyone else could benefit from reading his reply, and any other suggestions.

I'm looking to add a new constant and a new switched ("delayed accessory") circuit inside my dash, running through the fusebox, since I'm certain I'm overtaxing my audio harness. (Oh, lets see.. XM, cB, OHC, and probably one or two other things I've forgotten about.) I'm basically wanting to add my own beefy junction box behind the radio for my accessories, but I don't know where to start, esp. for a switched circuit. (More obvious is the constant power, although I'm sure theres a better way than starting at the battery.)

Suggestions?

 

Elaborate on what you want delayed?

 

for constant power behind the fire wall I put a fuse panel in my center console
I also fused it at the battery and ran a dedicated ground

 

When working on the electrical system, it is always good shop practice to disconnect the battery. In many cases, it is critical for your own safety.

I'm sure that there are a lot of unauthorized ways to find power for extra circuits. Here are a few I have used:

1) For minor additions, the usual mod method is to steal power from another circuit. The original designer incorporated a safety factor that will often tolerate another smaller load to be added in parallel. There is clearly a limit to how much reserve there is and, if you try to exceed it, the fuse will let you know.

2) If you have no need for the cigarette lighter socket, it is on a 20A fused circuit (shared with the Data Link Connector) that could be diverted for other uses. It is hot all of the time. A relay could be used to change it to keyed B+ if desired.

3) On 2003-back, there are about a dozen unused fuse positions in the dash fuse box. The various fused circuits in the dash box are grouped on bus bars that are each protected by a larger "parent" fuse in the Underhood Fuse/Relay Box. Adding another circuit would require that the fuse panel be disassembled and the new pins be inserted in the vacant slots. The stumbling block here is finding the special fuse panel pins which are not available separately from the dealer - I managed to get some at a salvage yard. To isolate my remote CD changer on its own 5A fuse, I just added pins to the unused fuse position #36 and jumped power from the B+ group of pins. Obviously, the size and number of circuits you can add is ultimately limited by the capacity of the parent fuse serving that group of fuses. And you must choose the correct power source for the desired function such as keyed B+, always hot, etc.





4) Adding a heavy duty circuit would necessitate going to the battery. Connecting right at the battery post is a bit awkward and exposes the terminals and wires to long term corrosion. An alternative that some people use is on the front of the Underhood Fuse/Relay box. After removing a small snap cover, you will see two nuts holding the end of the battery positive cable to a pair of studs. I have my larger add-on circuits connected here using ring terminals.

Here is the front of the Underhood Box with the small plastic cover removed. Note the use of heavy gauge wire and inline fuse holders.


The above arrangement is obviously going to be hot at all times. To easiest way to convert to keyed battery voltage would be by using a relay triggered by a keyed B+ circuit.

Any circuit connected directly to battery power MUST be fused as close to the source as possible. The wire gauge MUST be adequate for the load and the fuse MUST be sized to protect the wire. Full battery amperage is more than enough to do arc welding - needless to say, improper wiring is asking for a serious fire and/or personal injury. If you don't know how to do the calculations or how to make reliable electrical connections, be sure to get some experienced help. This is NOT the place to experiment.

http://www.kb1fpd.com/Wire-Gauge.pdf

 

it didn't occur to me that a relay would be the easiest way to get a "switched" circuit. Oddly, about 10 minutes ago I was at my truck, looking at those studs on the fusebox, thinking "boy, I bet thats what Bob is going to recommend."

Theres my project for tonight.. I'm rewiring all my accessories. I guess it will be easiest to stop by an aftermarket audio shop and buy some heavier-duty wire with inline fuses to attach right there at the fusebox. I guess I'll bypass the interior fusebox, and probably hit radioshack for some method of power distribution.

Bob, whats your feeling on grounding to the chassis vs. running a dedicated ground to the battery?

 

"delayed accessory" is Ford-Speak for circuits that are only powered with the key on, like the radio. Thats different from "Power Saver" circuits which are constant-on, but then time out after the key is taken out of the ignition, like dome-lights.

 

If you bring a fused, constant power wire back to the radio cavity, you can use the yellow/black in the audio harness to switch it using a SPST or SPDT relay. Then, if you want, you could set up a group of individual fuses in parallel to protect each of your accessories individually.


Chassis ground is a giant, low resistance conductor. As long as your connections are sound, there's no reason not to use it for general power.

Exception: very sensitive, low power circuits like those for engine sensors usually have a dedicated ground tied directly to the source (PCM) to avoid ground level errors and noise.

And, as I'm sure you know, you'll never see properly installed speaker or preamp wiring using chassis ground.

 

Right, I don't think anything I'm using is noise-sensitive enough to worry about ground noise. Most of my accessories (at least the sensitive ones, like the XM brain and the CB,) have their own in-line fuses, so I *should* be ok with running a new junction box in the dash, provided it offers some measure of protection against shorting out. I just hope my radio harness isn't so hacked up that I need to replace the wiring on it. I'm weighing the benefits of actually soldering connections in the dash against the possibility of melting interior parts or setting the truck on fire. I wish I'd have ordered that "cold heat" soldering pen!

 

I was told that those cold heat soldering guns are cool but you have to put more than average pressure on the tip to get em to work. If someone has personal experience here is a good time to chime in.....lol

As far as running constant power to a relay behind the dash, whats the biggest gauge wire you can run into a 30 amp relay then out to a fuse block. I wanna do basically the same thing as Wowak. It sounds like a really good idea. I too have a CB, OHC, and a few lighted switches that I wanna power. Thanks for all the help Bob.

 

You can use the link I posted above for a chart where you can determine the gauge you need based on anticipated maximum current draw and wire length. I tend to be a bit more conservative and would up the gauge to the next larger size (smaller gauge number).

 

i have the cold heat pen.... I prefer the wired up pen ( not the gun) The cold heat is too thick for me. and you have to use the tip and only the tip center. I like being able to use the side of the wired up pen solder tool.

 

Wanna sell it cheap? Shipping can't be much in-state.

 

here is how i went about adding circuits.

i took a male crimp connector, the blue ones(18-24gauge i think), take some dikes(wire cutters) and trim the male end a little, OUCH LOL :D
next place it into an empty fuse spot, use a tester to find the switched and constatant powers, i attached an 18 guage wire to it and ran it to my center console(you could run it wherever you want) and add an in-line fuse, i think i used a 20amp.

good luck

 

heres a quick and crappy diagram of what I'm going to build:



edit: BJB is Battery Junction Box, or more specifically one of the two studs that Bob pointed out earlier.

Considering that right now everything is running through a 15amp fuse without trouble, I think 12gauge wire should be adequate for the main power run.

 

Brian, the only thing I would add to that diagram is an inline fuse (30A, perhaps?) in the 12ga feed wire immediately after it leaves the BJB stud. Without it, you would have unfused battery voltage all the way to those individual fuses - kinda risky.

 

Oh, yeah, I already have the fuse, just forgot to draw it in.