CLEAN the battery terminals and posts. Then learn some troubleshooting. For this kind of problem you, really, can get by with a 12V test lamp
WHAT EVERY classic car owner should have.
1 Factory shop manual. You can download a whole bunch of 'em here and at MyMopar:
http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617
http://www.mymopar.com/index.php?pid=31
2....A 12V test lamp
3...A multimeter. Sears, auto parts, hardware stores all sell em. You can buy one that works great for less than 40 bucks. Even Horrid Freight has 'em
4....Three or 4 clip leads, test leads, alligator clip leads.
Next, AFTER you have cleaned the battery terminals, "get it to" fail. Then turn on the headlights. No lights? LEAVE the switch on Get out open the hood, 12V test lamp in hand
Ground the lamp clip and probe:
A....The big battery post RIGHT ON TOP of the battery post. Power? OK
B....Move the probe to the positive battery cable clamp right next to the post. Power? OK
C....Move the probe to the "big stud" on the starter relay. Power? OK
D....Look for the fuse link, going from that same terminal into one of the bulkhead connector terminals. Wiggle it. Feel it for heat. Take your probe and stick into that terminal. Power? OK
E....Still no headlights? But power in the fuse link/ bulkhead connection? WIGGLE the bulkhead connector, look for anything out of the headlights. Anything? Yes? You have found the problem
F.....If none of the above, get your hand up under the dash and wiggle the harness in the area of the ammeter and light switch. Anything? If not, it's time to get serious, time to garage the car and "get into" it.
Post back with results
READ THE ARTICLE below. This points up common problems, and also has a basic diagram of the main power:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
Follow along. From the battery, power ends up at the "big stud" of the starter relay. This is one contact of the relay, and also acts as a junction block.
From the stud notice "fusible link." THIS CAN FAIL. Then goes directly through the bulkhead connector. THAT CAN FAIL
Notice it then goes to the ammeter. More rare, but CAN fail. From the ammeter it turns to BLACK and goes to the WELDED SPLICE. Very rare, but this can fail. This is a few inches away from the ammeter in the black wire, under the dash. This taps off and feeds HEADLIGHT switch, accessory HOT BUSS in the fuse panel, power into the IGNITION SWITCH and a couple of other things. THIS IS NOT FUSED except for the fuse link