will the motor of a 86 honda hatchback 15s fit in a 89 CRX

Hello I take it it is the 3rd generation civic that you are swapping the engine from to the crx then yes should fit straight in might need to change the engine mounts over not sure if the wiring loom is the same though

you need to change the mounts and also u will need the whole wiring harness from the car your getting the engine from,,

It can be done, although it is generally considered a step backwards. Although the engineering principles of the designs are similar, nearly everything was all-new in 1988 for the Civic & CRX, so very little can be swapped directly without effort. Like Ed said, you will need at least the mounts and the wiring harness. You may be able to find more details at www.crxresource.org, but it may take some searching...