relay/fuse blocks (2 Viewers)

[coldtaco]

It helps to think through your circuits ahead of time so you order the right one. They come with one, two, or no internal buses.

The diagram on page 2 is helpful.

If I wanted no buses I might try the littlefuse as I do like that form factor.

I think I want at least a hot bus so I only have to run one wire through the firewall. Interesting about the thought of having a ground bus too.

 

[TreadingLight]

If you look at the diagrams I linked you'll see:

• 15305-2 has dual buses. One for the fuse connections and the other for pin 86 on the relays. If you want to power your devices from one source (I.e. your main battery) and you want to ground switch the relays, this is very handy and cuts down on wiring. Note you can insert the relays backwards and run a ground to the relay bus, in which case you can switch the positive side of the relays. I think you'd need to use resistor vs diode relays in that case.
• 15305-4 has no buses. If you have a mix of power sources (ex: main vs aux battery) and a mix of switch and power inputs to the relays (ex: ground switched headlight relays plus hot switched offroad lights) this is the way to go. This one is closest to how the littlefuse works but requires the most wire to make all those connections.
• 15305-5 has one bus on the fuse side. Use if you have one power source (ex: your main battery) and a mix of switch inputs to the relays (ground and hot switched). The bus will save some cabling.

I usually run an 8g cable to the bus and protect the fuse box with a 50a breaker as that is more than sufficient for my loads. The rtmr can handle up to 80a in total.

 

[cruisermatt]

Buss bars are pointless and just add additional failure points in my opinion. Just run your main feed wire into the fuse/relay box, and feed your other fuses/relays off it. Just like how all OEM manufacturers do it.

 

[TreadingLight]

OEM fuse boxes use internal buses like the RTMRs. I think you're talking about external bus bars for the hot side?

I do use external bus bars for ground connections. It is a handy way to collect and organize connections for pin 85 on the relays.

 

[cruisermatt]

Using the vehicle body for ground is and has been industry standard across all OEM manufacturers. Good rule of thumb to follow is if it has a motor you want it directly wired off the tree of battery grounds. Wiper motor, fuel pump, HVAC blower motor, radiator fan etc

 

[TreadingLight]

Using the vehicle body for ground is and has been industry standard across all OEM manufacturers. Good rule of thumb to follow is if it has a motor you want it directly wired off the tree of battery grounds. Wiper motor, fuel pump, HVAC blower motor, radiator fan etc

I connect the ground bus to a good chassis ground. It is just convenient collection point so you don't have a dozen 18g ring terminals all over the place.