I don't know the answer to this but I have a 18hp Cold water PW that I think also has a 20 amp charging system. I had a flojet pump hooked to it to help draw water out of the water tank when machine was in operation. The battery after a while (aprox 16hrs of use) would no longer have enough juice to start the Pw. So I disconnected the Flojet.
I forgot I have a Flojet hooked up to my battery also. One I rarely use. I wander if I could just connect the lights where the Flojet connection was? My guess is that the lights would have more of a draw. I was never really any good with electrical stuff.
The Hot water 12 volt systems use every bit of the amperage available to power the burner. I do not recommend adding lights to it. The cold water machine can run a couple of fog lights if the charging system is truely 20 amps. Better check first though. Get an engine shop to look up the serial # Type and Code to make sure.
Have you thought about adding a battery isolator to your truck's chaging system and adding a second battery to power your lights. The isolator will charge both batteries while the truck is running but will isolate the second battery while the truck isn't running so the lights won't run the truck battery down. A fully charged battery should power a couple of lights for a several hours and the second battery will charge while driving to and from the job or from job to job.
I already have two batteries in my Ford F250 deisel. I believe the reason for this is because of the glow plugs that are part of the starting system in the truck. Not sure if I could spare the power without risking having problems starting the truck.
I made one of those in shop class back in high school.
I ask my newphew about shop class.
His reply "what is shop class?"
They dont offer shop classes anymore!!!!!!
no auto,wood,metal,electronics,small engines,nothing hands on.
Even did away with builing trades.
If it wer'nt for those classes i would'nt have ever got out of there.
Then again if it were not for those classes maybe i could spell.
Have you ever made a BAR STOOL racer out of a starter motor and a battery? Man are they fast. 1 speed only.
I just added work lights as well, I used tractor type lights that can withstand the outdoors and everything that goes with it,then I purchased a generator the has regular outlets and 12 volt connections than I wired this to a box with a bank of switches that go to specific lights, since the 12 volt will not power more than two at a time, than I still have the regular outlets, if I need to run regular electric.