Anybody have a wiring diagram for a 1986 c800. It has twin tanks and can't get fuel pumps to run or switching to happen. Please help.

 

 

The electrically actuated fuel selector valve is spring loaded to feed the main tank to pump outlet operating mode when activated by a min. of 9.5 volts DC. make sure both tanks have fuel when using the flowchart.
The fuse for electric fuel pump and low air buzzer is a 7.5 sfe. Its located on the left side driver side. Looking at the bottom row of fuses. It is one row up and is the middle one located next to the longest fuse on that row.

 

 

Thank you so much. This does prompt a question though...if the fuel sending unit detects fuel empty does the system prevent the pumps from running? The reason I ask is because both floats no longer float. Thank you

 

So at this point, I could use some data from you. Would you state the year make model and any modifications you have made to the truck? Also, what events lead up to this issue. Has this always been a problem? Are you sure you have an electric pump vs a mechanical? Did you check the fuse? Why does the senders not work? Are they rusted and crusted?


On your sender, Duel tanks on the left (driver) side have a green wire to it. The other passenger tank has a green with red stripe.

At some point, you will need to use a multimeter to trace the issue down.

 

So it looks like there are 2 systems bimetal resistance type and electromagnetic system. The only truck that uses the electromagnetic is the L series.
Depending on what you have will dictate the test procedure.

 

This truck is a 1986 c800 ford. It was sitting for about 15 years. All systems came around to get it running with the exception of the fuel system. I flushed the passenger tank and sent power to the fuel pump to get it out of the woods. Both sending units are junk and laying on the bottom of the tanks. The fuse is good and harness visually appears to be great. The truck ran when it was parked. I figure if I have the schematic it will be easily resolved but maybe not. Please advise

 

Boy it sounds like you pulled a jewel out! I would love to see a pic of it. Where are you located? how much fuel did you put inside the tanks? Did you happen to change the fuel filter? When its day light, see if some of that rust slipped up to the carb and is clogging it. If you used the a clear fuel filter you will see rust particles in it. If its the metal canister open it to see if rust is in there as well. I had to use 2 fuel filters till I got consistent results. That happened to me even after I cleaned the tank one time.

You should have a primer switch in your truck. If that's the case, this is the way you should test your fuel system. Make sure your battery is strong and operate the primer until you expell some fuel into the a suitable container. I would disconnect at the carb. If you expell 1 pint in 20 seconds that's means your fuel pump is working but at the min flow. It will have 2 psi. 20 seconds is for the 370 and 429 motor. if you have the big girls 477 and 534 its a quart in 36 seconds.

Now your fuel pump is a dry motor. So it doesn't have a need to "shut down" if the senders show low fuel.

However, an oil pressure safety switch shuts off the fuel pump when the engine stops or whenever engine oil pressure drops to low level.

 

 

 

I cleaned the water separator and replaced the fuel filter after I cleaned the tank. Once I pulled plugs and freed the engine the only thing I was missing was fuel. I sent 12v to the passenger pump and the truck runs perfect. Oil pressure is killer and the truck runs right down the road. I just have to figure why I am missing power to the pumps and switchover Valve. I do not have a primer button but I will test the oil pressure switch. I'll keep you posted. Thank you for the help

 

THATS AWESOME!!! Great job!

 

May I ask a favor would you take a picture of the shifter linkage and let met know what transmission you have in it please.

 

Wow That think looks GREAT! I love it.