Add-a-Fuse Setup for Multiple Signal Wires

Hey everyone,

I'm looking to add more to my add-a-fuse setup, specifically everything I want to turn on once my key is turned. My question is: can I add multiple devices to a single add-a-fuse, or will that be too much for one circuit?




The add-a-fuse won’t be directly powering most of these devices. For example, it will only power the Raptor lights. The other devices, like my switch panel and headlights, are using the add-a-fuse as a signal wire — basically letting them know to power up when the key is on.


I have two scenarios in mind if this might be too much for one add-a-fuse:

1. Using a Relay: Could I add a relay with a fuse, using power directly from the battery? The add-a-fuse would just trip the relay and send power to the devices. My concern is if that would send too much power to the signal wires. Is this setup the same as wiring the relay trigger directly to the battery? (
   $12 Gebildet 12V Fuse Relay Switch Harness Set - 30A ATO/ATC Blade Fuse, 4-Pin SPST Automotive Electrical Relays with Heavy Duty 12 AWG Wires (Pack of 3)
   $12 Gebildet 12V Fuse Relay Switch Harness Set - 30A ATO/ATC Blade Fuse, 4-Pin SPST Automotive Electrical Relays with Heavy Duty 12 AWG Wires (Pack of 3)
   Amazon.com: Gebildet 12V Fuse Relay Switch Harness Set - 30A ATO/ATC Blade Fuse, 4-Pin SPST Automotive Electrical Relays with Heavy Duty 12 AWG Wires (Pack of 3) : Automotive)
   
   
   
   
   
   
2. Splitting the Load: Finding other fuses that are also ignition-switched and using them to distribute the load. I want to avoid this, though, to minimize the number of wires going through the firewall.

Would appreciate any advice or recommendations on whether the add-a-fuse alone is sufficient or if a relay setup is necessary here. Thanks!

 

If the current demand of all your accessories combined does not exceed 10A or so, you should be OK tying them together onto one Add-A-Fuse.

Having that circuit trigger a relay however would provide less worry (more-stable source of power/less chance of upsetting your truck's electronics), and also gives you ability to add even more accessories up to whatever the relay is rated to.

Also FWIW, the power wire going to the relay (the one connected to terminal #30 in your diagram) should be fused immediately right where it comes off the battery (using a fuse block for it is also fine). I don't like relays w/built-in fuses unless you can mount the relay right next to the battery (it adds another potential point of failure in the line since any wire more than a few inches long is already supposed to be fused).

 

most official wiring specifications generally agree to fuse within 12-18" of the battery, not directly at it.

but understanding the theory behind the specification is just as important. a 22-16ga wire coming off the battery is generally going to be it's own fusible link-- it's unsuitable for carrying full battery power, so will burn itself apart rather quickly in a dead short situation. but an 8ga or larger wire represents a larger heat load, which means a greater longer term heat/fire risk, where a 22 gauge wire represents almost no fire risk... ohms law at work.

 

Was speaking in a practical sense.
But yes, the longer the unfused part of the wire, the higher the potential for a short (and subsequent fire) becomes.