'77 F-100 starter problems, neeeed help

So right now i have a 1977 F-100 with a 302 in it that wont start. I've replaced the solenoid, i replaced the starter today, i replaced the old battery connectors bc they were full of rust. The only problem is, the truck still wont start. It's weird bc i can just turn the truck on and the starter revs up and makes a loud hissing sound but i havent even started up the truck yet. I've been working on this thing for weeks bc im trying to sell it. Does anyone have any idea as to what is wrong with this truck? I've try troubleshooting everything i just dont know what it is except maybe a bad connection from the starter to the ignition. Any help would be greatly appreciated.

Thanks,
Brennan  

Brennan This does not sound like an easy one since you’ve already done the easy stuff. The way to get through this is to keep posting until you get it fixed and then let us all know what it took.
My first question is when did this problem begin? What kind of work if any did you do before this happened, to get to this point? I like your choices for this last round of attempts but I don’t think you tested enough before you started replacing parts.
      I would start with the starter motor running by itself with the key in the on position. This could correct the other problems you mentioned. One of the next steps/tests would be to remove any small wires from the starter solenoid and then turn the key on. If the starter motor keeps running then you have a short or crossed connection between the ignition wire and the starter solenoid wire that signals the solenoid to crank the engine. (I’m sorry but I cannot help you with colors without a wiring diagram or a look see) If this is the case I would look at the ignition switch. At this age, (30+ years) the switch could be bad and may be where the faulty connection between the ignition wire and the cranking wire is taking place. If the starter solenoid only has one wire the color “should” be the same at the ignition switch. If it has 2 wires the rest of this procedure still applies as long as you can identify the “crank” wire. If you do not find the same colored wire at the ignition switch you will need to figure out which wire it is some other way. Hopefully the ignition switch connector has some type of marking or letters to indicate what the wires are for. If you can test the ignition switch with an Ohm meter you could test for continuity between the two wires for run and crank. As a reminder since an Ohm meter is checking for resistance in a circuit you will need to disconnect the battery ground cable at the battery. It should be an open circuit until the key is moved to the crank position. If there is little or no resistance between these connections in the key on position, then I would replace the ignition switch – not the lock- but the electrical part next.
    This can get pretty involved when writing about it and not knowing your level of expertise, you can let me know if I lose you.
    So for this post I will stop here. See if you can find where the solenoid wire is getting its power from with the key on and we will take it from there.
As always Good Luck and keep posting. It’s the only way we can help.