Working fine as in you replaced it with a 12V pump? Or working fine as in you just hooked the stock in tank pump up to 12V and its barely pumping fuel if any?
I don't mean to be rude but you do know you now have way under 220A for your lights and siren now that the ENTIRE truck is 12V now right? Instead of adding a 2nd 200A alternator and a 3rd battery to run just the lights and leaving the truck 24V, ALL of your load is now drawing from the 12V alternator; starter, headlights/taillights, turn signals, heater, gauges, it all adds up!
The reason I'm saying that is I'm going to become a volunteer firefighter next year and am going to do the same thing to my deuce when I get one. Without having to convert the truck to 12V!
Tm-america makes a really nice 2nd alternator bracket for the multifuel. A 200A delco 10si alternator plus a 1000 CCA group 31 battery will be more than enough capacity for lights and a siren. Plus everything else on the truck is stock for ease of parts availability, who's going to have a 12V multifuel starter on the shelf?