This site is mainly for the 95-99 Riviera. Not saying you can't get help here, but you would be much better off here, www.V8Buick.com
If the motor is running when you push the switch, then it must be a problem with the seat transmission. Should be fairly obvious if you can unbolt the seat so you can see as you power the motor.
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98 Riviera SC3800 All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU