Fuel Pump Won't Prime

Hello Everyone My Name is Justin I am new to the forum here! I have a 1985 F-250 with a 460 and dual tanks. I am having a bit of a problem with the old girl, the fuel pumps wont prime! I am most concerned about getting it to run on the front tank, The front tank pump does prime when I jump it from the pink and black wire at the solenoid. However I does not when I go in the cab to start the vehicle. I will give a short run down of what I have done to the truck thus far. I also do have a homemade iphone video I can post if thats ok showing what I have going on so its easier to see what I am talking about, I am new to wrenching and definitely learning as I go here lol. Anyways back to the truck so, to start I have replace the fuel tank the pump sending unit and everything to do with the front tank, that even includes lines vent and filler neck. After doing that I figured it is not a mechanical issue and that I need to start learning some electrical. (which on a side note is pretty fun, but challenging I may add) So first thing I had to do was replace the solenoid because when I was trying to crank it to see if it would start it was sparking and welding one of the connections to the solenoid. So with the new one that was fixed, from there I replace the pigtail on the pink and black wire at the solenoid and a new 20 amp fusible link in that wire. When I jump this wire (pink and black) I do hear the new pump priming but still nothing when I go to start it. after that I replaced the two relays. when that didn't give me anything I went in side the cab and checked the inertia switch and tried to jump it still nothing. So now I am wondering If there could be a problem with one of the wires going to the inertia switch, I am going to check them later today. Other than that I am kinda lost. I appreciate any help or information anyone can give me on this truck. thank you all for your time and have a nice day!  


Video- https://www.youtube.com/watch?v=kXxt1UEm2_Q&t=3s

Justin - I'm not 100% sure I followed everything in the video, but I think I caught enough for us to start wading through this.

First, you said that if you put 12v to the Pk/Bk wire that the pump will run.  That tells us that the right half of the circuitry in the schematic below is working.

However, you don't hear the pump run when you are cranking the engine?  That should put power to the Pk/Bk wire just the same as when you put the jumper on it.  So if you are sure that the pump doesn't run then let's discuss why that can be.

But if you aren't sure then I'd suggest that you pull the cable going down to the starter, which should be the big one on the rear lug of the starter relay, and then turn the key to Start.  That should send power to the fuel pump w/o spinning the starter so you can be sure the pump is coming on.

And if the pump isn't coming on then that says your starter relay is either bad or wired incorrectly.

Ok thank you Gary this was very helpful! I am going to give that trick a shot that you mentioned. Taking the lug off and seeing if I can hear the pump prime. Thank you very much for your help, I will report bad later with what information I find.

Ok so I disconnected the rear lug on the starter relay and went to crank the truck and I did here the fuel pump prime! I was ecstatic lol! but then kinda distraught because now I am really not sure where to look. Do you have any idea of where I could begin to look next. Thank you so much for your help!

So your fuel pump is running when the engine is cranking.  But the engine doesn't start?  Do you know for sure that it is a fuel problem?

What I would do next is to pull the fuel line off the carb, put it in a container, and jumper the Pk/Bk line to 12v.  You should see fuel come out of the line into the container.  If not, then you need to find out why.

If fuel does come out into the container, proving that you are getting fuel to the carb, then you need to figure out why the engine won't start.  I'd pull the air cleaner, prop the choke open, and look down the carb while opening the throttle briskly.  Do you see two streams of gas squirt into the carb?  If not then you have a carb problem.

If you do see two streams squirt in then check to see if the choke is closing.  It should close almost all the way in order to get the engine to start.  If it does and the engine still won't start then maybe you have an ignition problem.

Ok sorry for getting back to you so late Gary, it has been a crazy week. I am not sure it is a fuel problem that was just my best uneducated guess lol. Tomorrow I am going to pull the line off the carb and see if I am getting fuel as well as check the coke and carb.I did find out from the PO this week that when they had the truck apparently it need a new carb then! so I will definitely check hopefully this is my issue I will run the test before I go charging up my credit card just to be sure.  Thank you for your help and I will report back with what I find!