Joe, it could also be the change-over switch. This switch is a DPDT. One half of it (one pole) is used for horizontal and the other half is used for vertical. The pole for horizontal could be bad. Or it could be the feed line to it that is the issue. Or the joystick itself. It is worth inspecting and cleaning.
You may want to use the factory diagram for MY 88 or, if you go the Bentley route, be aware that the mirror pages are inverted. So you need to follow the diagram on page 970-91 that is wrongly titled "Mirrors 1984-1985". You have later mirrors with 2 motors per mirror. You may also find inconsistencies in wire colors. Good luck.
