Have you got a link to the lights?
Many LED lights will run on 12 or 24 V, and they often achieve that with a buck converter.
https://en.wikipedia.org/wiki/Buck_converter
One problem with buck converters is that the current they take from the supply isn't steady, and it turns on and off all the time, at 20 kHz or more. That switching can cause interference with the rest of the vehicle, because the current is varying all the time.
There are various things that you could try:-
- connecting capacitors in parallel with the supply as close to the light as possible
- insert a filter in series with the supply to the light.
- have wires for both the +ve and the -ve of the light going all the way back to the battery, and twist those wires together along their entire length
Other LED lights work with a simple resistor or with a current regulator. Those are less efficient, so produce more heat, than buck converters, and often have to be specified for either 12 V or 24 V, but there is virtually no electrical noise from circuits like that.
I have seen LED lights that work from either 12 V or 24 V without using a high frequency converter. The assembly was basically two 12 V lights run in parallel, and there was an electronic switch to put them in parallel if the voltage was over about 18 V.