On my 72 f250 4wd, I plan on using the original harness for everything it came with, except the radio. I want to start going through and cleaning it up and fixing what needs fixing. Is it better to just retape everything or do some use the wiring covers. Not sure what they are called. I have a partial extra harness that I was thinking of trying to keep wiring with factory colors or is there new wire that comes in smaller amounts if need be. Off hand, I dont think I am missing any plugs. I plan on doing the two relays for the headlights. Is it ok to run that on the main harness or would it be better to add that to the new harness that I plan on running the stereo, EPAS, and A/C. Forgot electric fan as well. Also have the 130A 3G swap going in.

 

Throw the original harness away. Wires are all old and brittle.

You can replace with a generic 28 circuit kit with add ons like firewall junction for about $470.

You can get a brand new OEM style harness for about $750. The OEM style would swap right in.

 

While not the easiest path I ended up using a power distribution box from a late 90's Explorer. There are multiple vehicles that use a similar setup so you are not restricted to just the Explorer. I grabbed it at a local u-pull for about $10 with as much wire as I could pull with it. I had several needs that led me to this. These included A/C, EFI, 3G, 7 pin trailer/brake controller, headlight relays, and more. My goal was to remove as much load on the ignition switch and the lighting circuits. I was able to do this without replacing any of the factory wiring under the dash. It all stared with a burned up circuit board behind the instrument cluster. The ammeter circuit had fried so I replaced the ammeter with a converted voltmeter. By doing this I was able to remove all of the shunt wiring near the battery and at the same time I did the 3G conversion which got rid of the regulator. I used one wire from the ignition switch that previously went to the regulator to provide the switched source to the 3G. I continued to add circuits to the factory starter relay but it got pretty ugly. That is when I went to the power module from the Explorer. It contains fuses and relays for nearly every load I had. If you plan it first, it also supports the 3G along with a factory mega fuse. By modifying the Explorer bracket I was able to mount it to the inner fender. I has switched and un-switched circuits and I run the AC, horn relay, EFI trigger, headlights, starter relay (for mini starter), trailer brakes and 12 volt supply, and more. Where needed I ran wires from under the dash to provide positive triggers for the relays in the Explorer box. The only full load that I have on the ignition switch are the wipers. If you are interested in going this route I can post pictures and describe in more detail how I incorporated the fuse/relay box. When I read that you were going 3G, AC, and fans (which you can power through the Explorer box) it seemed like a good fit and you won't have 10 separate wires coming off of the starter relay.

To complete the wiring, I used the factory low and high beam wires to trigger a separate small relay box mounted to the radiator support for the headlights using a fuse in the Explorer box. I used the factory marker and brake light wiring but replaced all of the lights in front and back with LED's and used LED capable flashers. This gives me a lot more light with much lower loads on the old wiring.

With EFI, a 4R70W conversion for the FE, aftermarket AC I gave up and ideas of keeping things factory/original and have a functional system that I feel is much better and safer than the factory wiring.

 

So far I have a very loose plan. I was just starting to draw out some of the individual wiring diagrams for some of the add-ons. I planned on some type of 12v key on terminal bay on a separate relay, like one of the continuous duty relay like a starter solenoid. I already have the parts for 3g swap, 2 speed mark 8 fan, EPAS, and Mark V dealer add-on A/C that was in a parts truck. After that, stereo and possibly headlight to the new set-up. Your system sounds a lot cleaner. I would definitely like to see what you have on how you did your fuse/relay box. Thanks for the feedback. I have been dreading this part of the build.

 

I would like to see what you did...Tony.

 

This is what I did for power distribution. I kept adding wires to the battery or starter relay and it became a mess. A number of vehicles from Ford and GM have under-hood power distribution boxes and the Explorer unit seemed to have what I needed but there are a number of Ford cars/trucks that have similar setups. This is the basic Explorer arrangement. Some may be a little different depending on the engine and accessories.



This is another view. Note that the 175 amp megafuse can be used for the 3G alternator. I had already wired mine with factory cables from an earlier Taurus that used fusible links. I may use the megafuse in the future The main wire from the battery comes in on the left lug and this feeds all the fuse and relay busses in the box. So, one large wire will feed the entire truck.




Starting at the positive terminal of the battery I have the starter cable (mini starter), 3G alternator main cable, the distribution box feed, and the Holley terminator and ignition box main feeds. In the distribution box with combinations of switched and unswitched circuits I have a main feed to the ignition switch, horn relay, headlight power to high/low relays, trailer brakes, trailer 12V, a feed for a trailer lighting relay arrangement, alternator trigger, EFI and ignition triggers, starter relay feeding the solenoid on the mini starter, and the power for the heater/AC. There are a few more but my memory fades. The box will easily support fused power to a separate fan relay setup or even fan relays if desired. The EPAS can also be fed. Many of the circuits I run through the box eliminated loads on the ignition switch. I used the green/red (have to double check that) wire that used to run to the regulator as a trigger that is hot in ignition and start. I used the old starter trigger as the trigger for the new relay. You can use the output of the relay to trigger a conventional starter relay if needed. All of my ignition is 12 volts so I don't use the resistor wire. If you are running a pertronix you can power the pertronix with one of the relays to eliminate another wire or two from the ignition switch. If any of you decide to do something like this I can help you layout the fuse and relay arrangement. I had to run a mini starter in mine because I am running a transmission adapter for the 4R70W mated to my FE. That kit includes the mini starter since the factory starter will no longer work.

This is the box mounted on my inner fender. I bent up the factory bracket to mount the unit. It can be unclipped and turned upside down to make changes if needed in the future. You'll see a few wired that aren't loomed and that is because I made a few changes when I swapped the Holley Sniper over to the Terminator X Max.









This is the back side of the distribution box. Note the cover for the main feed and the 3G alternator connection.



Front side of fuse/relay box

This shows the the megafuse. If I hadn't already wired my 3G I would have used this connection. It is probably a little safer than the fusible links. Make sure you use a cable suitable for this amperage.

Back side showing main feed

Main feed coming in. 175 amp fused side is for 3G connection - currently not used

This shows the inside of the fuse/relay panel. The only obvious change is that I replaced some of the maxi fuses with circuit breakers for the trailer wiring.


Fuses and relays

This is the relay setup I used for the headlights. I think the Superduty diesels have these so I snagged one at the pick and pull

Headlight relays

At the pick and pull, grab as much of the factory wiring as you can to get some wire length to work with. Several of the circuits for windows and wipers are daisy chained together. The separate the relays, you'll have to snip wires and in come cases move the connectors (easy to de-pin and re-pin) for NO or NC operation. The easiest way to get all the wires you need is to grab two of the boxes. I had spare relay lugs from some other projects but I was running low at the end. I believe some of the mini relays use connectors that are unique to Ford. To wire it all up, make a diagram of everything you intend to run through the box and note the relay and fuses for each of those circuits. Note that if you want to add more circuits the empty fuse or relay sockets by adding wires and connectors. I had about 5 circuits left over that are mostly unswitched and fused that I can use in the future. I just ran the wires out in a pigtail.

If you don't like wiring may not be something that you want to tackle. I found it kind of fun and it took me roughly a day to reconfigure the fuses and relays and another day to make the wiring connections. Most of the wiring in and out of the cab runs through some holes in the firewall just above the inner fender

Hope this is somewhat clear. Post questions here or contact me through the messenger if you have more detailed questions.

 

Thanks for all the info in the post. I will be reading and re-reading. I am leaning towards this route heavily now. I just happen to be making a JY run on Sunday anyway. Looks like list is getting longer. I am hopefully going to find a rear fuel tank set-up out of a 1990 f350 with the narrow frame rails, then some explorer electrical with lots of wiring, and headlight relays from not sure yet. I already had the 175A mega fuse with the 3g from a 1995 Taurus but I like how that is also incorporated into the box as well. I am not a wiring fan but not scared either. Just need to get this truck under my belt and done. Thanks again and will definitely have questions.

 

Ended up getting a 1998 explorer power distribution block today at the JY. 20$ and with a wad of wiring.


I was separating out the wires that were not connected to anything from other Y'd off sections of the harness.
GPatrick, did you find a wiring diagram for the bottom side of the box? That way you could just go by the color of wiring. I have literally been searching for over an hour. Or, did you open it up and start over. I opened the box up and was going to start labeling the wiring but closed it up thinking I would find some wiring diagrams of it.

 

I'll look for a diagram but If I recall I ultimately opened it up and started my own wire color table. Some, like the blower or the fuel pump relays are pretty easy to identify. On the relays that work windows or wipers I ended up pulling a lot of that and either replacing some of the wires with spares that I had or I would snip the leads that I still wanted to use and soldered a new longer wire and covered with heat shrink. I have a box of relays and wires that might have my color chart. You may want to create a list of what systems/loads you want to run through the box first and then use one of the diagrams I uploaded to label where you want them to reside. From that list, you can then identify the wires that go to the fuses or relays. You can be pretty creative when you look at your layout first and then worry about what wires you need to run underneath. A number of the circuits with low amp fuses have fairly good wires so you can up the amperage safely. The fuses where wire size matters more are the maxi fuses. You'll notice that the wire gauges vary depending on the factory fuses.

If you have any questions about specific circuits drop me a message and I'll send you my contact information.

 

I re-wired the entire thing. All of the wiring is bad at this point, no matter how well kept the truck is. Painless has a kit, but i went with American AutoWire. All new switches/plugs were included. wiring is similar to factory. and it's designed for modern lighting, horn, EFI, etc using built-in relays. I also upgraded to a 3G alternator, but after dealing with sizing issues I would probably do a 1-wire conversion if i had to do it again.

If you just replace a little here and there, you're going to have issues. If you splice everything together from a 20-year old salvage harness you're going to have issues although maybe not right away.

 

https://us.search.yahoo.com/yhs/sear...A2JXG_set_bfrq
Would something like this most likely work for the connectors in the power distribution box? Auto stores dont have the smaller multi tools for the connectors around here anyway. I traced all the existing wiring in the box and all wiring colors. I think I know what all I will remove from the box for now. I tried some small screwdrivers but couldnt get the wires to release. Napa is about all that I havent checked yet.

 

The relay socket connectors come out easy but you have to remove the red retainers first. They are a little tricky to remove. There are holes from the top that you can poke through to pull back the clips. Once you get the red retainer removed the connectors come out with just a little pressure on the clip. I think I used a small screw driver. I have a smaller relay box in the garage and I'll look tomorrow AM to verify and I'll try to take a picture. Took me a while to figure out the red retainers...

 

I too got all the wiring I needed from the 1994 donor truck the engine came from. But...I also wanted to replace in cab wiring, which was from 1967.

So, it made no sense to combine brand new wiring with 1994 wiring. So, I got one of these. Smoky_Diesel used this on his 2wd to 4wd conversion.

Combined with a new harness from Painless, it seems like the simplest thing. No going from one color to another and back to a 3rd. Easy crimp wires on box with waterproof bottom.

That's what I am doing and throwing both the 1994 and 1967 harnesses when done.

My $0.02

 

See post 12 in this link - https://www.fullsizebronco.com/threa...ay-box.186640/

 

In the pic, I will remove the headlight relays from the box and relocate to core support. Gaining the the two relays for choke and HEI. The fuel relay is just for future and wont be in use immediately. The #4 mega fuse slot will use a 30A circuit breaker like in factory ford diagram.