i found my relay shutoff switch on the left drivers side under the dash. its a small gray/white box and has 4/5 "tags" on it..it also has a ton of holes in it. if u have the fuse panel in the drivers side dash that flips down u can see it barely from there...take a flashlight and look better.
On a 1991 Honda Prelude 2.1SI, the Oil Sensor is located slightly above the Oil Filter.
yes
does a 1990 honda prelude 2.0 s.i have a pilot bearing
http://www.modifiedlife.com/1990-honda-prelude-car-radio-stereo-wiring-diagram/
No, the third and fourth generation are a different Chassis.
no
6.5"
NO, they have two completely different motors.
show me picture of where the water pump is located on 1991 Honda prelude si
the fuel rail
It's hard to say, as the question didn't specify what kind of solenoid are you attempting to fit, and the 1990 Prelude had a mid-cycle refresh which included an improved motor.
1990-91 Honda Prelude Si, not the 2.0si