What is this?

[Sean Sills]

I have attached 2 pictures. I am not automotively inclined so dumb it down. One pic shows 2 posts. What are these for? Other pic shows a red wire with an end on it that has never been connected. What is it for?

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[Caman96]

The red NEW fused wire could be for who knows what hackery aftermarket installation. The relay next to the fuse looks aftermarket as well. Where do the wires go? Did you follow them out to see? The two posts are auxiliary power A and B.

 

[GoToGuy]

Those two posts are " hot power" if you look under there is wire that goes to the battery. What extra stuff is added for the silver C/B and the fender wall relay?

 

[Road Trip]

Re: Red Wire question. IF this red wire is the factory wire that pokes out of
the convoluted tubing right behind the Underhood Fuse Block on our GMT400s,
then it is documented to be the "Fuel Pump Prime Connector".

For what it's worth, here's how this 'stray' test connector is documented in the '98 C/K FSM electrical wiring schematics:

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In order to prove that your bare red wire (that's missing the connector) is this factory test lead shown
in the wiring diagram, all you have to do is remove the fuel pump relay from the Underhood Fuse Block
and check for continuity from the end of your wire to the Underhood Fuse Block pin (cavity) B2.

Here's a photo of an undamaged factory 'Fuel Pump Prime' test connector:

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(credit: Photo taken by @LostX in his post: "Help Me Identify Mystery Connectors")

By the way, although our view is partially obscured in your 2nd photo, IF the Red wire from the
aftermarket inline fuse connector is connected to the GRAY wire coming from underneath the Fuse Block, then
according to the schematic above this could actually be the output (feed) from the factory Fuel Pump Relay
that is supposed to be connected directly to your Fuel Pump? If so, what was the problem that they
were trying to solve?

Q: Are you currently having any issues with the operation of your fuel pump, or are you (correctly)
just trying to understand the mish-mash that the PO left behind?

Let us know what you find and we'll try to help you get this all sorted out.

Cheers --

 

[Sean Sills]

I will update everyone once I finish. This is mainly for my knowledge because I thought these should be hot but never checked. You guys are a wealth of knowledge.

 

[GoToGuy]

The red wire with ring terminal is a factory wire , has non insulated crimp on wire and insulation. In the convoluted tube is a bare wire , some other upgrade?

 

[Sean Sills]

So the red wire withe ring terminal, is it supposed to be connected? I was doing some led wiring and hadn't put terminals on the bare.

 

[Road Trip]

Other pic shows a red wire with an end on it that has never been connected. What is it for?

Today I was able to locate the "Fuel Pump Prime Connector" on my own '99 C2500. Here's
what I found:

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Notice how it is coming out of one of the 2 larger diameter convoluted tubing that's run
to the Underhood Fuse Block. When I compare this to your photo it looks like that mystery
red wire with the bare end is coming out of a newer/smaller diameter convoluted tubing,
suggesting it was done by the PO? The only was to figure that out would be to trace it
back to it's origin.

Given this, I don't think that your mystery wire is associated with the the factory test connector.
You actually might find that inside/alongside one of the 2 older/larger convoluted tubing going to
your Underhood fuse block.

For what it's worth --

 

[Caman96]

I don’t see a RED wire with a ring terminal in his pictures. I do see an orangish/salmon colored wire with a ring terminal disconnected. The RED wire with mini-fuse looks new to me.

 

[GoToGuy]

Think age, exposure to sunlight , heat. Salmon is not a wire color. But old and faded red is. And restate the obvious.