aux relay fuse board - triggering

[resto_d1]

Hi All, I'm not the best with wiring/electrics but slowly learning.

My 90 currently has just a rear work light as an accessory. I wired this via a relay and understand how the relay works. Relay is using 12v cig lighter source as the trigger wire and has direct fused connection to battery.

I want to add a couple more bits to the car. This will be a 12v usb on my rear toolbox for torch charging, some kind of roof mounted fan/s for summer, my aux diesel heater. I'd also like to add a slimline sub with amp when my tool/heater box is complete.

I plan to do this via an external fuse box & relays. When looking at doing it the correct way, it seems I should have a relay per accessory.

This obviously means I'd need say 6 triggers from that one switched 12v source.

Is the correct way of doing this running my 12v trigger to a bus bar and then running a trigger from that to each relay?

Also, not sure what gauge wire I should use for the fuse box input/earth... I understand the power from battery + should have its own fuse/breaker also in-between the battery and the new fuse box.

Thanks!

 

[FlyingPete]

If they're all coming on with the ignition, you can do it with one relay if the current capacity is high enough. A 70A relay should be more than sufficient.
I would take a supply from the battery with a 60A fuse to the relay. Then from there, individual fuses of appropriate ratings to each of your circuits.

Otherwise, you need a relay for any circuit which draws more power than the switch is rated for. Proceed as above with the master fuse, then take supplies from there to each circuit fuse, then the relays.

 

[resto_d1]

Thanks Pete, I both understand and don’t at same time!
If I were to fit front spots for winter, and had my heater running at same time it would overdo the relay no?
I get what your saying - the whole accessory fuse box is dead until ignition is on and my high current side of relay is on feed from battery right after my big fuse/breaker.
I was going to go 6awg wire - which is capable of 100a, then 80a breaker, then fuse box which is rated to 100a also. I keep 20a safety in main feed. I was then going to run a relay off each acc. Which as you say would mean I need say 5 relays... I obviously want to do it safest way I can. I found structural mechanics easier to understand than electrics lol

 

[FlyingPete]

If you have lots of individual circuits, I would switch any high-current loads separately with individual relays. For example the front spots, they can take a direct fused feed into the relay, with a trigger from the main beam lights.
Having individual relays gives the most flexibility- such as your amp which logically should be triggered by the radio unit, so allow a distinct wire for that.
It's not cheap, but there is a modular fuse and relay system available which will do what you need. You build it up with whichever modules you need- in your case, probably a megafuse block, mini fuse module and then a couple of relay modules.