Rewire And Fuses Help

Hello all,

A quick question...I am totally rewiring my jeep for lots of reasons....Mostly a very creative PO. I'm comfortable with wiring but what i seem to be overthinking is, do the fuses go in line BEFORE the variety of switches, etc. or more after but before the accessories (ie Radio, lights, turn signals, etc.)? I am looking at several diagrams from the site but many do not show fuses.

Also, and to be clear the ignition does not have any fuses correct? Meaning hot power to the ignition switch is not fused until after?

Thanks.

 

The closer to the battery, the better the protection.

 

Thats what i was thinking but not seeing on the old wiring.

So should there be a fuse before the ignition switch too?

 

Dunno, none of my CJ5s or Willys Jeep pickups came with OEM fuses. Just a relay/breaker at back of the ignition switch, feeding the lights.

Might be a road hazard to lose your ignition unexpectedly.

 

If the jeep your working on is the 63 in your sig then you are far from original. The Ignition has no fuses and the circuit breaker feeds the head light switch and other stuff comes off there as well. the heater has inline fuse (can be any place in power line) same as turnsig flasher power is inline fuse (any where along the wire behind dash) no fuse for horn. It gets power from the CB on the headlight switch.

 

Yes far from original and not trying to go there really. Just want the best I can make it. I don’t have any circuit breaker as it’s just a after market generic 30amp ignition switch from FLAPS.

So is it safe to say that ignition is without fuse but anything after or wired right from battery should be?

 

Well, again speaking of hazards, it would suck if your headlights went out suddenly on a fast mountain road... many later vehicles continued to use a circuit breaker for the lights.

 

I guess I’m not sure of the actual difference between circuit breaker and fuse except for the resetting of it vs replacement. Guess I need to research.

 

Whether your restoring or not the goal is to make the Jeep safer and more reliable. A good place to start is the service manual from a later year jeep or other simple vehicle. Study the schematics where circuit breakers, fuses and fusable links are located. Stray from there with an aftermarket harness. Often times they are more cost affective to purchasing items separately.

 

There are obviously many different ways one can engineer a wiring system when starting from scratch. On my 3B, in addition to the cutoff switch at the battery and a 750 amp fuse there, I use a waterproof 120 amp breaker (EATON's Bussmann Series 187120F-03-1 Circuit Breaker | Waytek) for the main electrical supply for everything except the winch and starter (which are both wired direct to that cutoff switch). From there everything is protected by individual ATM style fuses and breakers. Probably overkill, but I now have 3 Bussmann 15300 series fuse/relay blocks installed with 15 relays, 40 fuse/breakers (EATON's Bussmann Series 15303-6-2-4 Mini Fuse Panel | Waytek, EATON's Bussmann Series 15305-1-2-3 Mini Fuse Panel | Waytek Wire). And all those slots are full-------

 

I just went through this, well sort-of, on my '66
The PO had added a ton of stuff but luckily hadn't chopped up the factory harness, so I was restoring it to close to factory.
The original harness had one thermal breaker pretty much everything ran off of and then a fuse for the turn signals.
Not the safest and not the easiest to troubleshoot. I compromised by adding a 6-fuse block on the firewall just in front of where the cluster lives. This allowed me to use the factory harness without modification. I added a heavy feed from the battery and ran two fuses switched and four unswitched. I continued to use the inline fuse for the turn signals and tied to the ACC position of the ignition switch, per the factory manual.
While I'm sympathetic to the point of view that a fuse blowing and suddenly loosing ignition would be bad, if there isn't any fuse then you could have an electrical fire instead and still have a sudden failure. Not better. I run pretty heavy fuses, 15-20A for the critical systems or whatever it takes to basically just protect the wire so if I have a dead short the fuse goes rather than the wire.
FWIW:
Switched: ignition, instrument cluster
Unswitched:Alternator, headlights, brake lights, horn

The thermal breaker on the headlight can suddenly turn things off like a fuse, but as soon as it cools down the bimetallic strip re-establishes the connection. If the short was brief enough you get your lights and whatever back pretty soon, hopefully before you drive off the road.

 

Fuse protects wire from fire.
You can go heavy on the fuse only if the wire guage allows it.
An auxiliary plug would have a fuse to protect the wire then the fan or phone charger might have an internal fuse to protect itself.
Be careful not to tie a bunch of fused circuits to a feeder wire that isn't big enough.
Also use a heavier ground wire than power where dedicated grounds are needed.

That's all I've learned from my 1lb halon fire extinguisher.

 

This is true, but I would not overthink it.

The purpose of the fuse is to interrupt the circuit if there is a short circuit. It might also protect from overload, but ideally you should design your wiring to handle the load under all conditions. I wrote some about fusing to the load in this thread: Headlights Relays In Absurd Detail

As mentioned, you want the protection of a fuse or fusible link as close to the current source as possible, thus protecting as much of the circuit as possible. In an automobile, we use the body shell as a ground path, and there are many ground paths offered to any one circuit. We can't interrupt the ground, and instead we focus on the hot side (positive on our Jeeps).

I would say that the fuse panel in a car has two functions; first, the branching power feed uses smaller and smaller wire, to economically adapt to the reduced power demand as the power reaches the devices. We could wire the whole Jeep with 4 ga wire, and place one big fuse back at the battery. Then a short anywhere would pop the single fuse and not burn up the wiring harness. This has obvious economic and space issues. Second, we don't want to disable the whole car if there's a short to the cigarette lighter (BTDT!) or radio or whatever. The system isolates a failure in the less-essential systems.

In summary, put the fuses where they will protect the most wire (close to the positive post of the battery), and use wire and fuses appropriate to the load.

 

When I first bought my Jeep earlier this year, none of the lights worked. There was also about 200 feet of random wires that had been added over the years that weren’t serving any purpose. I ended up pulling out every inch of wire and starting from scratch. I used a blue sea 12 position fuse block, although in hindsight a 6 position would have worked fine as my Jeep is pretty bare bones.

I looked into the “painless” wiring harnesses and the various knockoffs available on amazon, but at the end of the day it seemed like they would actually be more painful than just buying a fuse block and some good wire and doing it myself.

 

Funny, I went with a "Blue Sea" block (thanks West Marine) as well at first (6-position) but when I re-did things a couple years later went back to the old-style block for that vintage look.

East bay, so you're sucking a lot of smoke when outdoors too right now I imagine.

 

Have a pic of the old style block and where you got it? I already have mine in but not totally sure i like it fully....yet...Still wiring...

 

I just happened to have something nice on-hand, but digging in I notice Digi-Key sells them. Littlefuse brand is a classic and .25"x1.26" fuse size is the old-style standard glass fuse. The 6- position example would be part 03560006Z-ND for $21.50 but there are a dizzying array of fuse blocks available.
This is one I happened to have on-hand that looks a lot like the Littlefuse product. Boring and humble, but period-correct. Mounted askew because I found two existing holes that were the right distance apart and didn't want to drill another out of pride my fuse black was level. Later came different tie-strips to make it a 2-4 rather than a 3-3 split so I could break out alternator/headlights.