Damn, good question...I oughts to know these...take this all as a rambling guess.
It's late and hell week before the 4th so brain is mushy at best.
Speedo is a blk hose, doesn't come from motor, usually from a transom mounted pitot.
trim and tilt in '89 was 2 wires, one wht/gold, and a blk/?. They would be wrapped together.
tach is the grey wire. Tach is rpm's.
heck, it would be way easier if you stated what color wires you had? Kinda refresh the old gears between the ears...
blue is power the lights in the guages.
blk is a ground for each guage. These wires all come out of the loom except the blue. They do not come from the switch.
DO NOT USE THE BLK/YEL OR THE BLK AT SWITCH FOR A GROUND.
Similarly, do not use a red or red/purple from switch as power for anything.
A seperate accessory fuse block should be mounted and supplied with power and ground from the batteries for any accessories.
