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I built my fuseblock using a Bussman dual bussed box. I'm trying to determine what size fuse to use in each slot. I've read that in theory the fuse in the holder should only be as large as the smallest wire used in that circuit. Is this true? Because this will be a daily driver I did not combine as many of my wires as some do because I wanted to make diagnostic easier in the future. Because my fuse box has two busses I divided them into Battery Hot (hot all times) and Ignition Hot (hot when key is on). My fusebox is laid out as below:
Ignition - L1
1. Injectors Bank 1
2. Injectors Bank 2
3. Coils Bank 1
4. Coils Bank 2
5. Bank 1 Sensor 1 (O2 sensor)
6. Bank 2 Sensor 2 (02 sensor)
7. TAC (Pin C2 A9)
8. MAF Sensor
9. Ign/Crank (Pin Blue 75)
10. Neutral Safety Switch (2 wires)
11. Neutral Safety Switch (3 wires)
12. Dakota Digital Dash Controller
13. AC compressor relay
Batt + - L2
1. AC compressor relay
2. Electric Fan Relays triggers (3 relays 10a)
3. Fan Relay Power 1 (40a)
4. Fan Relay Power 2 (40a)
5. Pin Blue 20
6. Pin Blue 57
7. Dakota Digital Box
8. Fuel Pump (25a)
9. OBD 2
Even though I've combined the wires for all the injectors on bank 1, is it OK to use the same size fuse as was used on one of the original injector wires? I think since the original harness used 40 amp fuses for the fan relays then I'll do the same, and 10 amp fuses. Where I've combined several wires for the neutral safety switch, what size fuse should I use for those?
Below is a fusebox similar in appearance to the one I've used
It's going to be hard to say for sure without calculating exactly what every circuit needs, but I generally keep them closer to factory so I use the factory specs for fuses. If you have 22 fuses, then you have almost twice what the factory did. For example, the left bank coils and injectors are all run off one fuse the way GM did it and it was a 15A, so if you've cut that circuit in half, you may want to cut the fuse size also, so I would probably run 10A on them. Same goes for the two PCM constants, they are factory ran off one 20A fuse, you have that circuit cut in two also. The O2 sensors are ran in pairs, front and rear off 15A fuses, so you will probably be safe with two 10A. When in doubt, its best to err on the low side rather than high on fuse ratings.
What are you using the NSS for? Actual neutral safety and back up lights?
Go to the junk yard and find a truck with the fuse block under the hood. Pop the fuse cover and see what the factory fuses are for those locations. This will at least get you started in the right direction.
Aw man, I thought I actually had less than the original factory fuseblock. When I first started this harness project I had zero knowledge of this so I couldn't really retain what was what. If I'd known that I would have combined mine back like the factory had it. If I were to search for the original fusebox amps and what they were hooked to, what would you call that (I don't think a pinout would give the amps, would it?).
The harness I used had 4x4, so I had to eliminate some things. When it came to the neutral safety switch I didn't know what was needed and was wasn't needed. I knew the dakota digital dash would use the NSS for some information, but I didn't know what wires did what, so I just kept them all. I think the backup lights will still work as they were, though I couldn't really explain how the system works. I assumed it has to do with something on the column shifter switch.
Aw man, I thought I actually had less than the original factory fuseblock. When I first started this harness project I had zero knowledge of this so I couldn't really retain what was what. If I'd known that I would have combined mine back like the factory had it. If I were to search for the original fusebox amps and what they were hooked to, what would you call that (I don't think a pinout would give the amps, would it?).
The harness I used had 4x4, so I had to eliminate some things. When it came to the neutral safety switch I didn't know what was needed and was wasn't needed. I knew the dakota digital dash would use the NSS for some information, but I didn't know what wires did what, so I just kept them all. I think the backup lights will still work as they were, though I couldn't really explain how the system works. I assumed it has to do with something on the column shifter switch.
These are the fuses used by BP Automotive for their standalone fuse boxes:
As you can see, not a whole lot. Ignition power, battery power, the sensors, fuel pump, and each bank of injectors and coils. You should be able to figure out most of the fuse values from this, the fuse box lid for the donor engine may also list some of the fuse values.
OK, I've looked into every circuit and here is my best assessment of what size each fuse should be. If I could go back and do it again I would combine more of the circuits into one, but I didn't know any better when I started and now it's all finished. Please let me know your opinions or if you think I've done anything that may cause damage. There were a few I was somewhat unsure of, but in particular the OBD2 port and the AC relay. I thought the AC compressor didn't pull that many amps. I thought a 10a would work for the compressor, but the boxes I looked up on the site seemed to all have 20a for the compressor. Have I gone too high or too low on anything?
Ignition - L1
1. Injectors Bank 1 (10a)
2. Injectors Bank 2 (10a)
3. Coils Bank 1 (10a)
4. Coils Bank 2 (10a)
5. Bank 1 Sensor 1 (O2 sensor) (10a)
6. Bank 2 Sensor 2 (02 sensor) (10a)
7. TAC (Pin C2 A9) (10a)
8. MAF Sensor (5a)
9. Ign/Crank (Pin Blue 75) (10a)
10. Neutral Safety Switch (2 wires) (10a)
11. Neutral Safety Switch (3 wires) (10a)
12. Dakota Digital Dash Controller (5a)
13. AC compressor relay (Pin86) (10a)
Batt + - L2
1. AC compressor relay (20a)
2. Electric Fan Relays triggers (3 relays, pins 86) (10a)
3. Fan Relay Power 1 (40a)
4. Fan Relay Power 2 (40a)
5. Pin Blue 20 (pcm power) (10a)
6. Pin Blue 57 (pcm power) (10a)
7. Dakota Digital Box (5a)
8. Fuel Pump (25a)
9. OBD 2 (5a)
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Fuse sizes on custom fuseblock 
