Assuming the 12 volt setup and you have a voltmeter, I'd start like this with a totally assembled electrical system.
Measure and record the voltage between the battery's positive and negative posts with the key off.
Measure and record the voltage between the battery's positive and negative posts with the key off and the headlights on.
Measure and record the voltage between the battery's positive and negative posts with the key on and the headlights on.
If all 3 measurements above are not at least 12.5 volts the battery is either defective or not charged. Solve that problem before continuing.
Once you've posted those results we can proceed to the next steps.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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