Fuel and fuses

[CA Big Red]

So, last weekend I was towed home by a Ford.  I have a 78 K10 Stepside. The engine was starved of fuel and with gas in the tank, I figured it was a bad fuel pump or filter. 

When I got back home I jumped on this board and saw that people were suggesting to check fuses, so I did and sure enough my 15A for windshield wipers and blower motor was blown.

As soon as I replaced it, pimped the pedal, she fires up.

So, my guess is that I ran out if gas and when I switched tanks, without that fuse, she never really switched over.  So, right when I put that fuse in, it made the switch and I was able to draw fuel from the other tank.

That's my theory that I am hoping someone can confirm so that I know that I don't have to go replacing the switch, the sensors, etc. 

I also can't seem to keep that fuse from blowing, so ideas on that would be appreciated as well.


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[Captkaos]

The wipers should have nothing to do with the fuel selector wiring.  Are you saying if you pull the wiper fuse out you cannot switch tanks?

[CA Big Red]

Yes, I'm asking if there is a connection between the wipers fuse and how the tanks actually switch. 


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[CA Big Red]

In two instance, it seems when I replace that fuse, I'm able to draw fuel again.

Of course, I need to find out why that fuse keeps blowing.


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[Captkaos]

You didn't answer the question.  If you remove the fuse, can you switch tanks?  Are both filled with good gas?  The only think the switch does it move from one side to another.  I has nothing to do with pumping gas.

[bd]

Chris, I think he's saying the tank selector quits working and defaults back to the empty tank when the WIPER fuse blows.  His 78 truck uses the spring-return solenoid type valve. 

CA Big Red, the tank selector should power from the B/U TURN SIG fuse, unless someone moved the power tap.  The WIPER fuse is adjacent.

[CA Big Red]

I do lose my wipers, my heater blower and my signals. 

So, what are you saying is happening?


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[Captkaos]

Ah, thanks bd..
If it is blowing fuses you potentially have a short somewhere. 

[CA Big Red]

Why is it causing the starving of fuel?


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[bd]

Why is it causing the starving of fuel?

The 1978 factory tank selector valve is spring loaded.  The valve requires 12 volts to force it to the "auxiliary" fuel tank.  If you lose power to the valve because of a blown fuse (or other cause), the selector valve defaults back to the "primary" tank.  If the primary tank is empty, there's no fuel available to the engine.  Get the idea? 

As you acknowledged, the real issue is to determine why you keep blowing fuses.  Download and familiarize yourself with the 1978 Wiring Manual.  You'll probably need a PC to view it. 

The heater blower motor, turn signal/fuel tank selector, and w/wiper motor are each protected by separate fuses.  EXACTLY WHICH FUSE IS BLOWING?  And, do all of the mentioned appliances cease to function at the same time?

Also, do you have an electric fuel pump, or an engine-mounted mechanical fuel pump?

[CA Big Red]

Thanks bd!

 

This is the fuse I keep blowing. However, I picked up a new box of 15A this afternoon and so far so good. Threw on the wipers , heater blower and my turn signal and made it home. A good trip.

I think I do have a short somewhere, I just want to I make sure I don't also have a fuel switch of pr fuel pump issue too.


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[bd]

That's the back-up/turn signal/tank selector fuse.  As previously explained and as you've experienced, it could cause the loss of fuel supply. 

The red wire that plugs into the fuse block directly above the turn signal fuse doesn't appear to have a factory style connector.  Do you know what that red wire feeds?  Does it go to the tank selector switch on the dash?  What happens if you unplug it? 

But, the most troubling symptom you mentioned... the issue of the wipers and blower stalling when the turn signal fuse blows is inconsistent with how the cab was wired from the factory.  To clarify, are you claiming that when the turn signal fuse is removed from the fuse box the wipers and heater blower cease to function and when you reinstall the fuse e/g works?  Have you noticed any consistent pattern to the fuse blowing?

[CA Big Red]

Correct bd.  When that fuse blows, I don't have my heater blower, wipers or the turn signals. 

I pulled that fuse block above the turn signal this afternoon, but couldn't tell what it was for.  I will keep playing with it.  I think its stereo related, but I'll know more tomorrow when I have more time to keep figuring this out. 

Thanks for all of your help.  I think you nailed it.  That fuse controls the tank selector and as soon as I put a new fuse back in, it switched to the alternate tank and I was back in business.

So, now I need to find out what is causing that fuse to blow and possibly clean up why the wipers and blower motor on that fuse too...

Thanks again bd!

[bd]

Bear with me...

Answer each question, in turn:

What happens when you remove the "W/S WIPER" fuse?  Do the wipers quit?  Does anything else stop working?

What happens when you remove the "HTR - A/C" fuse?  Does the heater blower quit?  Anything else?

Using a test light, with the ignition switched ON, remove the wiper, heater and turn signal fuses then probe the fuse clips in the fuse block.  Are all three fuses receiving power?

Reinstall only the turn signal fuse.  Probe the fuse block clips for the wiper and heater fuses.  Which fuse clips are hot?

Connect a voltmeter, negative lead to the battery negative post and positive lead to clean bare metal of the cab.  Switch on all of the electrical accessories (e.g., blower, wipers, dome lamp, radio, etc.) and measure the voltage.  What is it?

[CA Big Red]

bd, with the big game today, I don't think I'll be able to get back to this.  I'll let you know if I do.