Correct Wiring Harness

What is the Watt rating of the LED's and the Halogen lights?
Each LED draws a lot less than a halogen light, but there are generally a lot of them in a light assembly and it adds up.

Most Halogen lights are around the 100W mark, my bit of research shows that a round ARB LED comes in at 90W, but a lot more light for your 90W, so something like that could probably be a straight swap

If you are going for a light bar where you have a lot more LED's packed in, it isn't hard to crack the 400W mark, in that case then your current loom might not be up to the task.

Will be no major differences except the fuse size and the plugs for the lights. If they are rated at 400w it would be pushing the rating of the relay.

If running two Halogen 100w lamps already, the loom is constantly supplying/ passing, at least 16 amps when switched on. More than 50 amps at instantaneous startup current.

The LED bar should have an amp usage rating. As mentioned already, if there are lots of LEDs then the total may be quite a bit more than 16 amps.

If you have 1 or two lightbars the total should not be more than the loom can supply. So knowing it's capability is required to ensure the LED bar/s are catered for.

Let us know the amps requirement of the LED bar and it can be worked out from there.

Not being compatible may mean the loom requires cutting and connecting to the LED bar wires simply because the plugs are different. Easily fixed by a competent electrical person.

Many light bars come with their own complete loom, so that shouldn't be an issue.