OFF the BENCH, CAMO
There is not a lot of workable option IMO and the little I understand
All things being said factory M998, dash wiring is NOT some M1165 special ECV harness.
I think
the fishing for wire numbers and looking for the letters is throwing a wrench into it. ADD the fact not enough "Y" s to tap in.
Here goes. Ground is ground.
ANY 40x wires are panel lights.
ANY 27x wires are power.
You need power any 27x. Need to go to the panel or speedo light 40x. There are three 27. Fuel, oil, temp and even the Voltmeter, but that is a 567.
Only two 40x wires available for the panel lights at the sockets.
Can't really go wrong. Now if you grab say a "Y" connector to TEE off 27x to feed tach or speedo power, NO problem. Same for panel lights. "Y" connector to 40x to TEE and feed the light circuits.
If the kit you didn't get, didn't have the "Y"s to couple in, then same thing... do your own "Y" thing. A proper peel insulation, wrap wire, solder, tape and note. DONE. Once you close it up, one will forget and still working a long long long time.
My post #39 has print of Speedo. Plug it in, ground and power 27x and light 40x.
Same for tach, power 27x and light 40x .
I charge $150 PER HOUR. "Y" connectors extra. TAPE cheap. This advice FREE, CAMO