Wiring Work lights to 12 battery box

Does the wiring harness include a fuse holder? If so, is there a fuse in it?

Check ... Does the harness allow you to feed reverse-polarity to the lights? LEDs require correct polarity, and it wouldn't even be the first time I have seen a factory harness cross-wired.

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Hi Nick,
I have just watched a video (here) on installation using a supplied harness. Have you watched this for procedure?

As, presumably, both lights are not working then it unlikely to be a faulty light itself so proceed to troubleshooting the wiring as follows.

There are a number off places where you could have made a mistake and suggesting a list of them may add even more confusion. However, a likely one could be the switch, assuming you installed one. The connections on a switch can be confusing. Try bridging (e.g. with a small screwdriver) across the switch terminals (with the wires connected) or removing the wires and touching them together. If the light works then it is either incorrect connections to the switch or a faulty switch. If the light does not work then the problem lies elsewhere.

If you have a voltmeter, use it to trace the progress of the positive supply progress through the harness. Connect the NEG prod of the meter to the NEG terminal of the battery then use the POS prod of the meter to follow the voltage. Start with the POS terminal of the battery and work logically along the POS wire. Do not jump all over the place.... trace progressively and logically. If you reach the last connection before the light itself and the meter is still showing a full voltage, this confirms that the POS circuit is good. So then repeat the test on the NEG wire by putting the meter POS prod on the battery POS terminal and use the NEG prod along the NEG wire in the same manner as before.