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Old 03-10-2017, 08:09 PM   #8
71CHEVYSHORTBED402
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Re: 12 AWG red in cab - What are these?

Quote:
Originally Posted by ray_mcavoy View Post
That is correct. Although these wires do not actually connect to any fuses in the fuse panel ... they simply go through the bulkhead connector assembly (which is sort of part of the fuse panel assembly). The 4 amp inline fuses are located out in the engine compartment (close to the battery/alternator ends of these wires) so they can protect the full length of these wires.

The way the black/white and black wires are connected to the junction block and 12 awg red wires serves to place the ammeter (battery gauge) in parallel with the 12 awg red wire that runs from the soldered splice over to the junction block. So in addition to serving as the battery charge wire, it also serves as a shunt for the ammeter. The majority of the battery charge or discharge current flows through that red shunt wire with only a small fraction taking the parallel path through the meter assembly (and it's black/white & black connecting wires). One can also think of it in terms of the meter responding to the small voltage drop that is present across the red shunt wire due to current flowing through that wire which (like all wires) has some resistance.

In any case, the current that flows through the battery gauge (and it's black/white & black wires) is quite small ... it only takes about 1.5 Amps for the meter to read full scale. So this circuit can safely be protected with those little 4 Amp fuses in the rubber holders.
Shunt, I had to look that one up. Great information. Other than that, I read where the "black" wire from #12 on the cluster to the junction block may also be brown and black. Apparently you've seen plenty of black. I'm color challenged, but my wife says it's black so I say black.
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71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assm. guide "kit" for restoring it from ground up. With assys, the guide accts for 1000s of OEM identifications and part numbers, all written in short order. 700+ images include assm, illust., charts, and points of interest. Much of the info. applies to all 67-72 GM trucks, and to a lessor degree all 67-72 GM vehicles. My build thread, and more on the guide https://67-72chevytrucks.com/vboard/...d.php?t=730025
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