Hi all. I'm new to the forum and new to working on trucks, so I appreciate any help.
My 1983 F-250 (7.5L 460, two fuel tanks, manual, carb) has a couple of strange problems. I discovered that the battery had run down recently; when I recharged the battery, I connected the posts, and immediately noticed that my fuel pump was running (due to fuel leaking out of a carburetor gasket; I've since rebuilt the carb). I assumed that the fuel pump relay had failed, but checked it and it was fine. The constant fuel pump running problem has gone away, but it seems I am now getting no flow from the pump -- the vehicle won't start, although the starter reliably turns the engine over. The only thing I did in between was plug in a new fuel pump relay.
After playing with the fuel pump relay a bit and attempting to start the vehicle, I now have a new problem. In key off, all of the dashboard lights are active! Obviously, there is some sort of wiring mishmash, but I can't find any good wiring diagrams. Any ideas on the problem, or where I can find a good diagram to check the wiring? Anybody have a fuse box diagram?
Sounds like a problem similar to the one I have been working on. You should be able to unsnap the cover on the fuse panel on drivers side and the fuse size and description are molded into the cover. When you disconnect the starter at the solenoid (so you can hear what is going on) and turn the key on to the start position you should be able to hear the fuel pump you have selected (front or rear) Then you need to follow the wiring to the very back of the engine to find the oil pressure switch (you actually should find two and the one you are looking for is on the drivers side of the truck)which controls the power to the fuel pumps when the engine is running. You can unplug the connector to the oil pressure switch and jumper it out and the you should be able to hear the fuel pump running when the key in in the run position even when the engine is not running. If the fuel pumps are running in both situations you should be in business. As you probably know the excess fuel is routed back to the tank whenever the carb bowl fills up. Good Luck!!!!
Just an update...I discovered that I was getting no voltage at the inertial switch (or where the initial switch was, as it has been jumpered around). Fuse was intact in fuse box, but battery side of the fuse was only getting ~0.43 V; a couple of minutes later, 12.1 V (my battery is a little low right now), when the key is in start position, but after trying to start again, back to 0.43V. I am going to go through the tedious process of tracing lines to see if I have poor contact or another path to ground somewhere, but voltage should be the same as the battery if there is no current, so I am at a loss. Any ideas before I start pulling tape off wire bundles on the way to the battery?
It does sound like a poor connection somewhere. If it where to ground you would have smoke. You will get 12v through a poor connection until you put a load on it. Your meter is not enough load to pull the voltage down through the bad connection, but the fuel pump is. Try to keep a load on the circuit when you use your meter.
Check voltage at fuel pump cutout relay pin 4(yellow wire) should be connected to the inertia switch and should be 12v. Pin 3 on relay should be 12v when relay is activated through the oil pressure switch. Jumper that oil pressure switch out to remove any doubt as to whether it is working. It is kind of tough to change out, but you can unsnap the connector pretty easy and put a jumper across it. Then turn key to run position to pickup the relay and fuel pump. As I understand there are two versions of the 7.5 liter "hot fuel" systems on 1983 Fords. The only documentation I have is a Haynes Repair Manual No. 36058 which covers 1980-1996 pickups and broncos. If you look at the "please read" stuff on this forum I believe that there is something that shows the dual fuel pumps on our trucks.