No head or tail lights

I've got a 01 and the other night everything seemed fine as I drove to pick up my girl.but then the high beam indicator light dimmed and my head and tail lights went out as well as most of the dash lights except the hi beam indicator stay on but very dim. I checked the bulbs,fuses, relays and the light switch itself and they're all good. My friend told me I'm going to have to check the power and ground connections and I'm not sure where they are located or the percedure to do so.

 

Alternator rectifier or diodes bad?
Belt loose/slipping?

 

No I checked the alternator and it's fine. Belts are all snug no shipping

 

What was the voltage under load at the battery ?

Here you go your EWD every thing you need to trouble shoot your truck

 

Thank you for the wiring diagram.much appreciated.
The load is at 12.4v at the battery with the key off and the light switch on. And with the key off when I just turn the running lights on the tail light relay starts clicking like a turn signal then when i turn the light switch all the way on it makes a low humming kind of sound but still on and off like a turn signal.
With the engine running and lights off the voltage at the battery is 14.47v. The hi beam indicator light is very dimly lit. Then with just the running lights on Voltage is the same but the indicator light is slightly brighter. And with the light switch completely on the indicator light is bright no matter if the switch is on hi beams or low and the voltage is 14.47v the whole time. But I did just find that both front running lights are blown. I. Going to check the rear ones now