Although my setup is going to be more complicated than this, I put this together to help elucidate my question.

- Traditionally, I see people running setups that typically include a mix of relay and non-relay (direct) circuits. My question is, the main feeder wire to switch panel needs to be able to handle the total load of all circuits, and the switches themselves need to be able to handle that load as well, correct?

So, I've got switches capable of handling 20 amps, thus, in the diagram scenario there are 3 x 5amp direct circuits and 4 relay circuits. I am assuming the draw to close the relays is well under 5 amps total, which would make the switch panel circuit under 20 amps total.

Are these assumptions correct? I ask because it seems like I see folks running much higher loads than 20 amps to their switch panels without sufficient relays.

Some examples of accessories I have or am looking at purchasing:

- LED Rock lights - 72 watts (6 amps) over a total of 8 Pods
- LED ditch lights - 40 watts each (80 watts total, 6.7 amps)
- LED backup lights - 20 watts each (40 watts total, 3.3 amps)

These are all of the lowest draw lights I'm planning, everything else is significantly higher. My conclusion is then, that I could run maybe 2 direct circuits max, and everything else is going to need to be on a relay. The other option I was considering is that I could provide a dedicated power wire to some switches (instead of piggybacking them) and that would allow me to approach the 20 amp limit rating of each switch. So, for example, in the above scenario, a single power circuit would provide power to all of the switches that controlled relays, and then dedicated hot wires would run to each of the circuits for lights 5, 6, and 7.

Is my math working out or am I missing something here?

That's up to you.. I would wire the switches to the relay contacts and run the light circuits current across the relay contacts for each of the light circuits.

This way the switches are low current and in groups.

Each circuit amp load should never go up to 80% of total current fuse capacity.

I would fuse the circuits in a group. So one relay powers the group of lights.

If the lights are individual then maybe a few on each relay.






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OK, thanks, so that gets to my real question, which is, isn't it just best to put all the lights on relays and run very little current through the actual switches. That's what I was planning to do but I wanted to make sure it wasn't overkill to run 12+ relays

...and subbed! This is what I'm talking about Doc3g. I hate wiring. For what it's worth my personal plan once I moved to a higher number of switches was to run a relay on each light. So yes I too was looking at 10 relays down the side of the engine bay. Electrically inclined folk might get their flame throwers out now...

Fellows. Its always best not to current across switch contacts because in time they will oxidize and fail. With relays, you let them take it on their contacts as they are designed to plus you can put all the same relay in for you entire projects and keep one for a spare.

Even if you are only pulling 5 amp across the current contacts put the 20 or 30 amp relays in.

What's really neat is that you can positive or negative switch the relays to activate and they dont care. So I mostly negative switch them to be different.

They are low current solenoids and will do a good job for you as long as you dont buy Chinese junk. They do take a little current to work but its mostly in the ma and you can buy the pigtails so if one would happen to go you just change it like a fuse


I have faith you can build these circuits and fuse both the switch side and the loads sides for safety.



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Also watch if you guys want this circuit to be alive when the ignition is off. You want to wire it so the relay isnt energize when everything is off so you dont create a parasitic drain in your rig. I would tie the power for the relay feed to switched power source .

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Thanks, I picked up these fastronix relays, which are probably way overkill but they had stellar reviews. I also got a couple of 100 amp relays that I'm going to run to a tap-a-fuse in the fuse box so that the power distribution modules are only energized when the key is on.




On a related note, my dash mod for switches 11-15 came out pretty good

I guess the only problem with using Ground to control the relays is that you can't light up your switches, since they rely on the power from the input to light up....

You could always tap the relay power contact when the switch is on it loops back a lights the illuminated switch that way you know the relay is functioning properly too.

Several ways to accomplish the same task.

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Ground side switching is 'safer' electrically. If the wire running into the cab to the switch grounds, all you get is your load turning on, not a blown fuse or burned wire.

Appropriately fused, either way works though...

-Charlie