Chassis electrical system

Which wires and what has you worried? If you sent an image it didn't make it.

Okay, the wires where there are multiples of the same color with the colored cap over them are factory splice points. They look strange but they are OE. Normally they would either be taped up or run inside the loom. The first image is what the schematic shows but what you found is what they actually look like. All the wires run back, get crimped together and capped. P0110 is intake air temperature sensor. The common failure with them is in the connector or in the harness where the wire gets chaffed through. The fastest way to test it would be using a scan tool that can show you the intake air temperature. If the IAT reads -40 (40 below zero) the circuit is open, broken wire or bad connection. If it reads +284 degrees or more the wires are shorted together.
To test it without a scan tool set your meter to volts and unplug the connector. With the key on check the voltage at pin 3(Yellow with green stripe), you should have 5 volts. If you do then switch the meter to ohms, connect one lead to a good ground, then touch the other to pin 4 (brown w Black stripe) in the harness connector. You should see zero ohms or close to it if the circuit is okay. If either wire tests wrong you found the problem.
As for the DLC issue, please ask that as a different question, we try to keep topics limited to one problem to make searching the site easier. Oh, and what sites are you referring to? Just so people might get a heads up.

Hmm, I sent a reply, but the system must have eaten it. The DLC wiring you have is correct for your vehicle. That is because the standards at the time were only applicable to vehicles made in the US and only required engine ECU access for imports and that is all that is in your under-dash connector. The rest of the systems are accessed through the under-hood connector I see in your 2nd video. In the third video there are a number of non-factory quick taps. Those are used by people trying to add things like remote start or alarms or replacement radios. They are well known to cause electrical issues because of the way they damage the wires as they are installed but places like Best Buy and others still use them because they are faster than doing things correctly. Does it have remote start, or an aftermarket installation of lights, radio or something else?
The last video where you think those are the O2 wiring, you are likely correct. They use a shielded wire for the signal feed that then gets coupled to the system ground once it gets into the vehicle, it looks like someone removed those from the protective tape and loom they should be in, but they look normal for a 97 if they are out in the open.

Those trucks were built in both Japan and the US, and they sort of interchanged some parts. So that sticker was probably printed as needed and they didn't change the connector graphics. I go by the actual wiring diagrams. In this case the wiring diagrams do match with the connector pin counts.

That is the internal number for that version of the board. They use the same board in multiple applications and then print on it the different options based on the silk screening. So, one version might show a position as R4 but the version for another use shows as R6. Same board, different parts. The ID number shows which it is.