Packrat chewed wires--what was this?

[1985_C20]

1985 C20 Pickup. (resto project has not been started up in over a year) I had what I think was a packrat chew a wire. The wire that got chewed was a red wire coming off of some kind of terminal block on the firewall (up high between center and driver side) (see "A" in the photo). This red wire that got chewed went down and went into a little black square thing about half the size of a small matchbox and on the other side of the small black matchbox looking thing two other red wires came out of the bottom going down (see "B" in the photo) and went into a loom on the wiring harness. I made the assumption this minature black matchbox looking thing was just some kind of 3-way butt connector so I installed a new wire crimped on a ring terminal and soldered it to the other wires finishing the 3-way connection with heat shrink. I was showing a buddy and he asked me how I knew it was a 3-way butt connector? --and he said maybe it was a resistor/capacitor or diode of some kind. I hadn't even thought of it. The wire was chewed right down to little black square matchbox looking thing so it could not be re-used and I threw it away. Can anyone help me out with an explanation as to whether that thing was just a little black square 3-way butt connector--or was it something else?

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[CalSgt]

I believe the black plastic was just a factory crimp...

BUT, the section of wire you replaced should probably be a fusible link not just standard automotive wire. The terminal on the firewall is connected to the battery through the starter and possibly the alternator and is otherwise unfused. The fusible link should be replaced so you dont burn your wiring harness up in the event you get a direct short.