Oil Pressure gage help?

hey, im new to my 1991 Celica SX, sorry, ummm, i dont know what its called in the states, ST184 5SFE right hand drive anyway, i think its what you call a GTR, anyway, just a quicky, can i run an aftermarket oil pressure switch from my standard sender switch?i mean,can i just cut the wires and solder them 2gather to the corrosponding wires on the gauge,and another quick question, i have some friends with 1991 celicas aswell(all 5SFE) and they all use Air-Flow metre's near the air filter element, except mine, mine uses a Map-Sensor near the throttle body, does anyone elses celica have this? or has mine undergone a camry or MR2 engine swap at some stage of its life?I have a manual, and it doesnt say anything about a map sensor, and all the ones in the pics have Air flow metres??its a good thing either way, it makes it much easier to put some attractive chrome inlet pipes on....until it comes to some sort of electrical fault i spose.