Confusion on fuel and more.

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projectmidnight74

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Mississippi
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Eddie
Truck Year
1974
Truck Model
C10
Engine Size
V8
I am starting to understand that 1974 was a very odd year for these trucks. My issue is this. I have discovered that the shop did not install my new signal wire for my new tank and sending unit. I am going to do it myself but I am unsure where to route it to. In the past I have read where some say it plugs into the fuse block. Fory truck that location they mentioned says bat fused. I am unsure what that means. Where does this signal wire go once I get it installed is one question. Lastly. I have about 4 wires that are all carrying voltage that don't have a home under this hood. One green and somewhat insulated, one yellowish looking, one goldfish looking and another I can't figure out. Where could these possibly be going. Pics attached and any help would be great.
 

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dsteelejr

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First, get yourself a wiring diagram. From the main page on this forum go to Reference Library, then wiring manuals.

Are you running a single or dual tank system? You said the shop didn’t add the signal wire for your new tank. Is the new tank a replacement for the factory single tank or did you add a second tank?

In the wiring manuals the fuel sender circuit is # 30. For ‘74 the diagram says the wire is 20T-30, meaning 20 AWG wire, I presume the T is the color tan (later years it was pink), circuit # 30. Assuming you have a single tank, the fuel gauge wire starts at the instrument cluster plug. It runs to the bulkhead connector behind the fuse block where is passes through the fire wall. Under the hood to runs along the firewall to the passenger side then goes under the cab along the frame to the top of the fuel tank. Contrary to what you were told the wire doesn’t plug into the fuse block.

As for the other wires, I can’t tell from those pictures what those wires are for. I know there is a yellow wire that powers the ignition coil when the key is on. A dark green wire (circuit # 35) goes to the temp sender. It had insulation bc the sender was near the exhaust. Not sure about the goldfish color. Do all your gauges work? Could be for something not used anymore, like the idle stop solenoid. By now factory wires are so old that colors have faded. Reds look pink, etc. If those wires go to the bulkhead connector you could use the wiring diagram to figure out what they are for based on their position on the bulkhead connector.

It’s a blessing and a downfall that these older vehicles are simple and easy to work on. The downfall is that there is often an untold number of previous owners, many of whom hacked up factory wiring harnesses, made shoddy, half assed and full assed electrical repairs, plus added their own special projects to the mix. If everything else works and those wires don’t go anywhere then it’s anyone’s guess what someone was trying to do. If they have voltage then you should secure them so they can’t short.
 

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projectmidnight74

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yes this was a single-tank system. The gauges work, but again, untangling this has had its challenges. While attempting to remove the cluster once, all the old plastic started breaking around the cluster so I had to glue it all back and leave it be. Trying not to buy another one in other words. lol. I will research that guide once more and try to figure this brown wire out and get it installed. Thanks for the help.
 

projectmidnight74

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Update!
We dropped the tank. Found the fuel sending wire wasn't even run, just cut and connector sitting on a brand new tank smh. I am just no longer shocked at this point. We are changing the fuel lines to run outside the frame rail due to the 3 inch exhaust and electric holley pump sitting so close to the exhaust that its causing vapor lock. New line will come up by passenger side, into fuel pressure regulator and over and into carb. Will update with results. Vapor lock was causing severe issues after warm up due to exhaust pipe being so large. My dumb idea. But for now, in theory this should help. Pump will also be located away from the exaust and to outside frame rail. Wish me luck.
 

Radiohead

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Instead of mounting that fuel stuff on the outside of the frame rail, is there a chance to fab up a heatshield Instead? Hate to see a fuel related incident in the future.
 

Old Guy Bill

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Originally those trucks have a shield, but it was designed for 2 1/4” exhaust.
This pic from another thread shows it.


You must be registered for see images attach
 

projectmidnight74

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Instead of mounting that fuel stuff on the outside of the frame rail, is there a chance to fab up a heatshield Instead? Hate to see a fuel related incident in the future.
Tried that originally, I will post the pic when I find it. But yeah, summertime heat, and the large exhaust was a huge factor to make the change. Mississippi heat has no remorse. Also purchased heat shielding for the new fuel line that we're running. Was told that was overkill though lol.
 

projectmidnight74

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Originally those trucks have a shield, but it was designed for 2 1/4” exhaust.
This pic from another thread shows it.


You must be registered for see images attach
Yeah, I learned fast that what I felt was cool on paper, wasn't really the best idea. But by that point I was $600 bucks in on an exhaust system. May as well see what happens lol. He's a rowdy little small block but he wont hurt a fly. Widowmaker exhaust makes it sound pretty radical lol. But if this doest work, ITS GOING UP FOR SALE!
 

projectmidnight74

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Engine Size
V8
You must be registered for see images attach

In the red circle is the previous location of the components minus the heat shield. Somehow it was removed. Under the hood was also wonky. So we stripped it all.
 

Turbo4whl

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Why aren't you using the engine mounted fuel pump?
 

projectmidnight74

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Since everything was fresh from the motor to the suspension my bright idea was to just go electric for fuel. Again, I am new to building anything other than an audio system lol. This has taught me a LOT!
 

projectmidnight74

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Mississippi
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Eddie
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1974
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C10
Engine Size
V8
Update.
We are almost finished with repairs. New speedo cable installed.
Tank remounted.
Lines moved to the top of the rail away from the exhaust and the fuel pump was relocated. Tomorrow we plumb, pressure check, and fire em back up. Lastly, I finally found the dreaded fuel-sending wire. After getting pissed I was not finding it, dropping the tank, and seeing that they took no care to re-attach the dam thing if you go back to the original post, You can see that first picture with the blue tape on it, THATS THE WIRE I WAS LOOKING FOR THE ENTIRE TIME.
I couldn't find it until I got a new gadget for probing and applying voltage. SMH! Boy have I learned some stuff through this sequence of events.
 

projectmidnight74

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Mississippi
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Eddie
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1974
Truck Model
C10
Engine Size
V8
Update 2.
Had to replace fuel pressure regulator for one that was designed for carburated engines. We went with a holley style 12-803.
The install is complete and pressure adjusted but we cannot fire. I am having an issue with a slight leak on the inlet fitting for some reason. I have tightened the bejesus out of the thing and just applied some pipe sealant from permatex. Is there any way to avoid this from happening. we are ready to get this thing back in action.
 

projectmidnight74

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Mississippi
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Eddie
Truck Year
1974
Truck Model
C10
Engine Size
V8
Update 3: we have no leaks and fuel pressure. I want to say thank you to this community. I have been into automotive stuff my whole life but never had the guts to touch anything other than electrical work. Today we have successfully completed a fuel line rebuild and relocation of a fuel pump. We will fire today and dial it in. And we will finally see a fuel level with the gauge and have a working speedometer. You guys rock.
 

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