Ambulance electrical problem

So this past weekend I was participating in a "lights & sirens" fire company parade with my 1973 Superior ambulance, and while driving with all lights and sirens operating, the car kept stalling. It would restart but with all equipment operating, it shuts off. Any ideas, alternator, generator, batteries, something else?
 
Check your battery connections, and also have the batteries checked for weak cells. If you are moving slow, and you are putting a heavy demand on the electrical system, the alternator will not be able to produce enough electrical current to keep the batteries charged. If you have a battery switch, I suggest using only one battery, so should you deplete all the current in that battery, you can shut it off and get the car started on the other battery. Also carry a good quality heavy duty jumper cables with you, because you are going to need them one day. I will bet that your car has a very large siren on it, like a Federal C6 or a Q? They are definitely energy hogs, unlike a Super Chief.
 
Even with modern rescue trucks and ambulances, I keep the unit in first gear while moving and in neutral with the engine revs up when the parade stopped. High ampacity alternators need a certain rpm before they will deliver their rated charge. Older trucks had a manual throttle to handle this and modern units often have an automatic version applied when the truck is in park.

Paul's comment about a Q coaster is very true.

My 1976 has a generator and 2 batteries, but as I replace PAR emergency lamps, I give consideration to more expensive (and energy efficient) LEDs although I realize this may upset some.
 
Generator in 1976? Unless you are using the generic term "generator", your car should have an alternator. The difference is that a generator produces DC (direct current), and an alternator produces AC (alternating current), which is then converted to DC to charge the battery. When GM originally started installing alternators in the early 1960's, they continued the term "generator" in the parts books. Later on, after the alternator had become a more popular term in automotive literature, they changed the term from generator to alternator.
 
defiantly time for a system tune up. with duel batteries always change them in pairs. for some reason a new and old charge differently. but cable ends and connections need to be looked at. cleaned and on that car bigger is better for them. the #4 you get down to the auto store is not carry to carry the load. a number one will but if it worked last year and doesn't now it's most like corroded cable or a bad battery. the advice of keeping it in a lower gear and when stopped neutral and faster idle is sound. also work the siren, wind up short let it coast repeat
 
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