Another way I used to find out the alternator wasnt working without having a multimeter or common 12 volt testlight. .Because I made many road rescue breakdown calls for alot of years.And I had barely no tools except for screwdriver or jumper cables.Or did who I was stopping to help out broke down .Carefully touching a screw driver to back center of alternator case.Feeling for the elctromagnetic pulling effect gave you a idea what alternator was doing .And if I had a bad regulator Id bypass it and full field it .And turn on alot of things headlights etc to compensate the load .Off subject when I use to diagnose how bad a timing chain was on scene .Was with pair of gloves grabbing fan belt to move crank pulley.Or socket turning motor if I had the socket. But with distributor cap off observing rotor movement in relation to rotation of the engine.Lets you know it time to replace timing chain by very little lack of rotor movement .And you wont find this in those books.refered to.You will NOT find this "procedure" in ANY recognized shop manual, "Haynes" type, "Motors" or any other automotive text

Its up to the individual and what diagnosing tools/equipment they have or know how to use
what works for you might be this
CHECKING FOR A DRAIN. With EVERYTHING in the car off, and verify that any glovebox/ trunk/ etc lamps are out, unhook one battery cable WITH THE ENGINE OFF and hook your test lamp in series between the cable and it's terminal, see if it lights. A double check is to THEN hook your multimeter in the same connection IN AMPERAGE measurement and see if you can measure any drain. Be careful to start in the highest amps scale.

With a meter or a testlight depends what your using.Starting with testlight .You want to pull one fuse at a time to isolate the problem area when hunting down a short with a testlight.Make sure all connections all clean and tight and you have good grounds.And I make sure every switch is off and doors closed .So not to get a false reading.If you had a compass available to you.It can trace current

And checking - grounds This is how I always checked my grounds.I hook up a 12 volt testlight with the clip on the + pos on the battery.Or whatever source of+ power you have available to access in your working area.And when you touch the pointed end.To what your checking to see if its well grounded it lights the light.If not theres a problem.Its the opposite hook up of testing for voltage.And having alot of mopar for 30 + years with the usuall wiring issues.And done about 35 and counting mopar related wiring jobs on others cars .Number 1 mopar Issue grounds noumber 2.Amp gauge and its connections it housed in metal dash frame insulated by paper thin cardboard. fuse box connections and bulkhead terminal connections and condition and continiuty of the wires .Ignition switch terminal connections Ive seen alot of burnt terminals on the 70s cars especially in this area. Also at the starter relay where the fuseable link is often bypassed .Are all areas prone to issues.And this electrical system from day 1 wasnt state of the art.And now the cars being much older these electrical sysyems and known trouble prone areas.These issues surface

Electricity is lazy and will choose another easier path and cross circuit.And make wierd things happen.

And anything that carries + positive battery voltage.And is coroded or loose .Then you get high resistance .Wires getting warm connections hot and that familar plastic burning smell

And if your adding optional equpment.I go by the old school if you want to flow more water you need larger pipe .Heavier wire for load devices