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I'm working on a 1979 C-65 chevy truck. It has a gas tank on

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I'm working on a 1979...
I'm working on a 1979 C-65 chevy truck. It has a gas tank on each side with electric fuel pumps. Sometimes the pumps run, sometimes they don't. I need help diagnosing.
Submitted: 3 months ago.Category: Classic Car
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Answered in 1 minute by:
9/13/2017
Classic Car Mechanic: rpmdiag, Tech and Instructor replied 3 months ago
rpmdiag
rpmdiag, Tech and Instructor
Category: Classic Car
Satisfied Customers: 8,306
Experience: Since 1975
Verified

Hi, I'm Ron and I will be helping you today.
Stand by for a moment while I prepare your answer.

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Classic Car Mechanic: rpmdiag, Tech and Instructor replied 3 months ago

Okay, then we already established that they do work and run sometimes which means the wiring and pumps are good at the tanks.

We need to check relays under the hood in the power distribution box and also check for power from the ignition switch as well.

Please understand that I don't know your skill level or tools
you have to assist us. Also understand that I can't see, smell,
hear, or touch the vehicle either, so your patience is
appreciated. JA is a great Q/A site, but it does not replace a
repair shop. So please don’t shoot the messenger if I have to
deliver bad news:)
If you are satisfied with my answer, I would greatly
appreciate a 5 star rating now before you leave the site and I
will still assist you after you have rated me too if another
question pops up. I don’t get credit for helping you until
you rate me

Thanks, Ron

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Customer reply replied 3 months ago
No problem. The truck has a engine primer switch. When pushed the pump will run on either side using the selector switch. I'm guessing it's a relay someplace, I need a detailed description of where it is.
Classic Car Mechanic: rpmdiag, Tech and Instructor replied 3 months ago

I said that it was inside the power distribution box under the hood near he battery. All the relays are marked on the cover of the relay box. If the relay is good, then there is an ignition switch issue. most of those relays are interchangeable too.

No diagrams available on that due to the age.

Thanks again and please remember to rate me 5 stars now
and keep this link in case you need me again later on.
I don’t get credit for assisting you until you rate me

Ron

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Customer reply replied 3 months ago
These old trucks don't have a power distribution box. They have a few fuses under the dash, and a wire connectors on the firewall. I can't find the relay. Without a wiring diagram we are shooting in the dark.
Classic Car Mechanic: rpmdiag, Tech and Instructor replied 3 months ago

Then that relay has to be on the fuse box. If push comes to shove, we can follow the wiring back from the tank to the relay. The only other place that may have a diagram of something that old would be the library. There's always more than one way to do this:)

Thanks again and please remember to rate me 5 stars now
and keep this link in case you need me again later on.
I don’t get credit for assisting you until you rate me

Ron

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Customer reply replied 3 months ago
You're not helping me one bit. I don't want to tear the wiring harness apart. If you don't have access to a wiring diagram, why would I give you any stars?
Classic Car Mechanic: rpmdiag, Tech and Instructor replied 3 months ago

The wires are in color codes to follow them back and do voltage drops on them. There's no magic here, you do have to work with me here a bit. It's not that hard to follow a circuit.

Ron

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Classic Car Mechanic: rpmdiag, Tech and Instructor replied 3 months ago

Thanks again and please remember to rate me 5 stars now
and keep this link in case you need me again later on.
I don’t get credit for assisting you until you rate me
My goal is to assist you in the repair of your vehicle by
supplying you with well educated information. I may not
always have the exact fix you wanted to hear, but my job is
to get you on the right track, which I always do. I can’t hear,
see, smell or touch your vehicle from where I’m at, so your
understanding of that is greatly appreciated. There are no
magical answers, but I do my best to guide you in the right
direction.

Ask Your Own Classic Car Question
Classic Car Mechanic: rpmdiag, Tech and Instructor replied 2 months ago

Please understand that I don't know your skill level or tools
you have to assist us. Also understand that I can't see, smell,
hear, or touch the vehicle either, so your patience is
appreciated. JA is a great Q/A site, but it does not replace a
repair shop. So please don’t shoot the messenger if I have to
deliver bad news:)
If you are satisfied with my answer, I would greatly
appreciate a 5 star rating now before you leave the site and I
will still assist you after you have rated me too if another
question pops up. I don’t get credit for helping you until
you rate me

Ask Your Own Classic Car Question
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rpmdiag
rpmdiag
rpmdiag, Tech and Instructor
Category: Classic Car
Satisfied Customers: 8,306
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Experience: Since 1975

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