Evening all, got a 84 D-150, w/ 318, went to start it today and had nothing, threw charger on it, nothing, jumper cables, nothing, looked at battery cables and they are nice and clean, have power through the firewall with test light but under the dash, I cannot get the test light to "light up" on any of the fuses, wire harness' or anywhere. no lights, fan, wipers, absolutely nothing works, I did have a glimmer of hope when the dome light lit up, but as soon as I turned the key, all is dead again, that only happened once, can someone please advise if they ran into this before? talked with dad on the phone and I have all power to the right places under the hood, but once it goes through the firewall, it seams to go dead, all wires under dash look good, nothing burnt or corroded.....HELP please!!

Pull the bulkhead connector (firewall) apart and clean all the contacts first, and make sure none of the contacts are pushing back thru the plastic block. You may find a burned connector. Afrer it is bolted back together after cleaning, It helps to have a friend there to push on each wire from one side, while you push from the other with a small screwdriver.
I have had this trouble on my 84 and 83, but it was lighting circuits. Use dielectric grease before bolting the connector block back together. Check for hot to the ignition switch also. If you have hot in, but not out, bingo. I had a switch go bad and had the same symptoms.
I hope this helps.