grab a test light or make a test light. your life will become better. they are easy to operate, ground the wire on the light and touch the pointy end to a power source-the test light will light up.
hi beam-to test the headlight socket first try the test light with the clip grounded to a good ground and test the socket for power-headlights on. try hi and lo beam. make a drawing of which wire does what. that should help you figure out which wire is supposed to be ground. then connect the test light wire ground clip to that ground terminal and then touch the pointy end to the hot wire in the plug. headlights on of course. if the test light doesn't light up then you have a bad ground in the system. if you have no ground the power will go through the element to the socket, around the socket to the other element and back feed through the system until it finds a ground somewhere in a connected circuit. sometimes it is a marker light or a dash light bulb that sullies a ground. usually the light will be less bright. for a headlight a lot of the time it is a bad ground on the rad support where the headlight ground wire screws on. try a jumper wire from the frame to the ground wire to see if the hi beam headlight works. if so fix the ground problem
dash light bulbs-yes they need to be inserted into the dash to work otherwise there is no ground. the bulb socket only has a single wire on it, right? it needs to plug in for a ground, assuming the dash has a good ground.
horn-the one wire with the barrel connector is likely the one that would go to the horn contact on the steering wheel. if that wire is grounded the horn should blow. it is the contact under the wheel that grounds the wire to make a circuit and blow the horn.
here is a link to a thread that has a wiring diagram in it
http://67-72chevytrucks.com/vboard/s...d.php?t=550576