I have a 1983 F250 w/460. I am changing out my Rear pump/sending unit. I got the the tank back up and connected but when I went to put the NEG cable back on the battery the pump started running without the key in the ignition. A previous owner had snipped the rear tank harness. Now I know why.
Any ideas on this?

Thanks,
Eric

 

You have a bad oil pressure switch or somebody has bypassed it or the Starter Relay.
OR
Somebody has rewired the system that did not understand it.

Could also be a bad Fuel Pump Relay.

 

I forgot to say that my front tank pump turns on when the the key is turned to the RUN/START positions and the tank selector switch is on the front tank. Yesterday the tank selector switch was still on the Front tank when I tried to hook up my NEG battery cable.

 

Could the fuel pump relay be bad for 1 tank and not the other?

 

Does the rear tank quit when you turn on the key and the front tank runs?
Does the Front tank run with the engine not running?
Does the front tank stop and rear tank start running with key on when you switch the switch to rear tank?

 

Question 1 answer: I did not try to put the key in, I will try that tonight.

Question 2 answer: The front tank pump runs as soon as I turn the key to the run position. Is that how it is supposed to work?

Question 3 answer: Refer to question # 1 answer.

 

No but I said that about the Relay before you gave more information.

 

NO, the pumps are not supposed to start until you turn the key to the start position and the starter relay (solenoid) comes in.

Here is an updated diagram showing that.

 

If the pumps are only supposed to kick in in the START position then my front tank is wired wrong also. Could it be wired on the wrong post on the starter relay?

 

No, it is more likely that the oil pressure switch has been bypassed.

 

Was there a 1 wire pressure switch and a 2 wire pressure switch made for these trucks based on if you had a engine mounted pump or an electric (tank) fuel pump? My truck has a 1 wire oil pressure switch.

 

You should have two oil pressure switches. One for the gauge and another for your fuel pump system.

It's obvious to me(I think to subford as well) that a previous owner has rigged this whole system to make the truck run. We are giving you diagrams and troubleshooting info on the assumption you have a stock system, and it has had a failure somewhere.

Now it seems nothing is wired like it's supposed to be originally. I think this is what is causing some of the confusion in troubleshooting.

The way I see it you have two choices.

1. Go through the whole system, wire by wire. Print off the above diagram and check off every part that exists, and replace anything that is missing, trying to get it wired back up like it was. This may call for a trip to the junkyard to find another truck with a 460 and dual tanks.

2. Wire it up your own way to make it work. This will probably require more work than you think, especially when you throw in the sending unit and switching it from front to rear. But a couple of switches and lots of wire, you could make it work.

 

The diagrams seem to show that it has both, an Oil Pressure Sender for the gauge (one wire) and an Oil Pressure Switch for the Fuel System (two wires).

There were two posters about two months ago that had a problems with a set up like yours. You may be able to talk to them also with the PM system.
Here is the URLS:
https://www.ford-trucks.com/forums/s...d.php?t=502369
https://www.ford-trucks.com/forums/s...d.php?t=498154

Are you finding all of the rest of the Fuel system devices that are in the drawing or has someone removed all of them?

 

Where is the oil pressure switch (2 wire) located? I have a 2 wire harness near the 1 wire sender on the back of the engine, behind the carb. The harness does not hook to anything near there.
Everything else in the diagram is there.

 

My 460 does not have this system but I would think that they had a "T" with both the sender and switch screwed into it.
Also I have never seen a system like yours but I do have all of the 83 Manuals and wiring drawings.
I can only go by what you tell me and then I try to help you by looking at the information I have and give you a suggestion.