you haven't provided enough information to understand your proposed setup. Certainly it is possible to connect all three modules in parallel, but you have to know the actual current draw of each module, and the current ratings of the relay, switch and fuse.

Questions:
1. Does each LED harness have its own switch, fuse and relay?
2. Does the LED module documentation have a current rating? The KoC page you linked to states "LED power 40 watts", but since the input voltage range is 10-30V, there is probably a voltage regulator in each module that will draw a little current itself..

The total current draw for 3 modules is probably around 10A, so you definitely are going to have to use a relay. If the relay you have is rated for 20A or more, just parallel the three modules at the switched side of the relay, paying attention to polarity. Fuse should be 15A, located as close to the battery (or wherever you are picking up the 12V supply) as possible.

 

Each harness has two relays (JD1912 12V 40A), there's also a fuse box in the harness containing two fuses (32V and 15A). The switch box has two switches (1 for flood light, 1 for the halo rings). None of the light bars came with any sort of documentation for specifications so all the information I could find is online.
The thing that is confusing me is that the there's 3 wires going through the harness: Positive (red), Negative (black) and white (trigger?). I believe the white wire is due to having a 2 separate switches on the same switch block? Either way, if I connect all 3 cords into the one harness it shouldn't blow the 2 relays and 2 fuses correct?
Thanks

 

Halo rings?
You didn't mention anything about halo rings ... do you intend to be installing and controlling halo rings with this system in addition to the flood lamps?
The 40A relays sound like standard automotive relays, and one of them should be easily capable of switching the ~10A load current of the parallel-connected LED flood lamps.

 

OK I've had a look at the site, and it's unclear what the 40w refers to - each LED or the entire bar (I'll assume the whole bar).
There are halo rings around each light, so that's where your two relays come from.

A pair of 40A relays should be fine (one for halo, one for the main LED), paired with 15A fuses to drive all 3 bars.

I'd be very wary of the claimed light output & wattage of the system. They seem overststed which is common with Chinesium LED products.

For reference - https://www.diodedynamics.com/stage-series-6-sae-dot-white-light-bar-one.html - not as pretty though, but the light output will be far superior (and likely cheaper).

 

amaclach -

Thanks for paying more attention to the KoC advert than I did.

Looking again, the light bars do appear to provide both primary LED lighting as well as "halo" lighting. But, if four LEDs provide the primary lighting, where does the light for the "halo" effect come from? There must be some additional LEDs for the halo effect, hence the dual relays and dual switches.

But, there should be no difficulty in paralleling the primary LEDs on all three units and switching them with one relay, and paralleling the halo LEDs on all three units and switching them with the second relay. One pair of control switches, two relays, and three parallel-connected light bars.

 

From the Ops original question....
Yes, one relay will do it all

I know it’s been answered but I’m going for the low hanging fruit

 

spend the money get a SwitchPro