How many multicores you got coming out the throttle box?
If the second loom is PT related it's either going to be for a second station or as Pol says, you have 2 variations of age between engine & controls - I think
the older ones had a separate PT loom, because it was an expensive optional extra so the loom came with the PT. Your engine looks a bit newer than the controls, so you may find that pevious owner has spliced the new "everything" cable form the engine into the remotes, and not bothered to remove the old "extra" PT cable?
Mine has a spare Grey for the optional temp switch for what it's worth.
If they all go back to the engine, you have lots of free wires for gauges! If not, I see a weight saving opportunity!
Oh, and for checking the "send" to the tacho, any needle meter with an "AC volts" will work - It will give slightly random, but constant readings. (Send" is basically connected to the alternator coils, and the tacho counts the pulses).