I am having problems with my '86 F250 (two fuel tanks and dash switch) draining the battery with ignition off...seems like one of the fuel pumps is running after I shut her off and the fuel gauge is intermittently not reading the correct level...anyone have any advice? Thanks,

 

Another 460 equipped truck with electric fuel pumps. I wonder how many of these things are out there? All of them eventually give trouble. You didn't say anything, but if you just bought this truck, someone probably had problems with it, and incorrectly hot wired the pump to get it to run.

If you have owned this truck and it's stock and not modified, I would suspect the pump relay is stuck. Look over in the driver's side fender area for a relay and unplug it.

 

I have only owned the truck for a year. Within this time my mechanic has installed a fuel pump under the hood to address some problems with the truck starting and running, which appeared to help until the past month or so. Back in August I had some mice take up residence during a camping trip and suspected that they cause the recent problems, removed the dash and inspected the wiring and fuel tank switch...no obvious damage from them. I talked to the mechanic recently and they suggested that I install a primary switch to main power to solve the problem, but I wanted to investigate myself before turning over the truck for electrical problems$$$. Thanks for your response it is appreciated greatly. I will look for this relay and tinker with that before moving forward with a new switch. While working on the truck today I did notice a fuel pump "reset" type switch on the passenger side floor board up underneath the heater ducting. Interesting is the fact that the fuel level indicator for the front tank was not working properly until I fiddled with the switch after I loosened it from the dash mounts, but it did not permanently solve the problem of the battery drain.

So this fuel pump relay is under the hood on the driver's side?

 

Who knows what you have now if they added a fuel pump under the hood. Your fuel pumps are inside the tanks. I am assuming they abandoned them, and are trying to pull fuel through them with the add-on pump.

If they are trying to make the factory pumps run, and the add-on pump also, then that seems a little complex.

What you need to do is figure out which pump is running all the time. If it's one of the in tank pumps, I am going to assume it's not needed anymore. If it were my truck, I would pull the tanks down, pull the sending units out, and get new ones but don't buy the pumps. Then put a piece of hose where the fuel pump goes, and put it back in. This should also fix your fuel guage problem, since 99% of the time the sending unit is the problem with the gauge not reading.

Put it all back together, and just use the new add-on pump under the hood to pull the fuel forward to the engine.

 

Is the relay a small grey control box sitting on the driver side fender?

 

No, i think you're talking about the DSII ignition module there - small, gray box about the size of a sandwich mounted on the plastic wheel cover.

 

alright because i replaced that and it didnt fix the problem. so what exactly does the relay look like?

 

My understanding from others here is this:

 

I dont know if you tried to post a picture but it didnt work

 

Let's try this:

 

thanks i will look for it when i get home

 

The factory fuel pumps on these are fed by a fusible link on the starter solenoid when cranking, then through a resistance wire fed through a fuel pump relay actuated by an oil pressure switch on the back of the engine. Depending on when and possibly where it was built there are either one or two relays. 85 and early 86 seem to have used two relays, later 86 did away with one and used the tank selector valve to do all the switching. On the gauge, it could be the selector valve or the sender itself.

Yes, Franklin, there are a lot of 460s with the hot fuel handling package, also some 351W equipt ones.