i understand you found a relay that is not meant to be there.
im asusming this is a standard automotive 12v 20 or 40amp relay (same as the ones for the window motors) and it has 12v always which would be the expected voltage from the wire that connects to the temperature switch at the top of the thermostat housing.
the question is, what else is connected to that relay ? because a relay is just a high amperage switch that triggers using a small current (certainly a strange decision for a fan override but not necessarily a "wrong" or dangerous approach)
my point is, you may find that the relay is connected to a hidden switch inside the cabin which is used as a override.
my fan override is just a switch to ground inside the cabin next to the side mirrors control. but that instalation is fully mechanical. and if you were going to install it using a 555 timer circuit, a relay (although personally i'd use a mosfet) would be the "standard" approach for someone to ground (aka short) the temperature switch line.
my point before forwarding the information that you asked for is that the description you given does fit in with a instalation that would be acceptable IMO (sure others may disagree)
i can help with very little information as far as harness connectors.
BUT i can tell that theres one on each side behind the wheel arch.
from my recolection they included all the lights wires + the boost signal, O2 sensor, reverse swtich from gearbox and some spare connectors which i always assumed would be used by FED/ROW/JDM cars.
there is a bunch of wires that
i assume run through the bulk head somewhere for the injectors, MAP, TPS and other engine related sensors which i would assume include the one you seek.
from memory there should be
2 harness connectors below the water tank which i would espect you would find one of their wires going into sensor your refering to. but i cannot remmebr ever finding where these connectors follow through in order to get inside the cabin.
unfortunately for you. my car is all back together (so is RonR's) and i cannot think of anyone at the moment with their clam shell out that would be able to easily check what you seek.
only further advice i can give is to use your phone, set it to record video and turn the flash on before starting to record, and follow the wires from the relay to figure out where they go and what they may be connected to.
you can always come to Durham on Monday 28th see the classic car show, id have a look at that relay and would be in a better position to advise... for whatever my knowledge is worth...
