What car you looking at fitting it to ? Lcr engine code ?
There's a thread on fitting an oil temp gauge if you use the search but pretty much route the wiring from the engine bay up behind the air box and though a rubber grommit behind the pollen filter then to where ever you want it in the cabin ( I took the wiring feed off my headlight switch )
As far as the sender on the lcr at least above the oil filter is a plate it screws onto, on that plate is the space to add a temp gauge sender. Just undo the bolt acting as blanking plate thread the sender I wanna saw its a m10 and attach to everything else.
Hardest bit is routing the wiring behind the dash, the rest is straight forward. Just time consuming I did in 2/3 hours.....