I had same problem. Turned out it was corrosion on the solderless (crimp style) connector on the hot wire at the ignition switch. I think as engine speed increases, more current goes from the switch to the electronic ignition. If there is any resistance (from a corroded connector), it results in a voltage drop.

I solved the problem by replacing the solderless connectors at the ignition switch with solder connectors. While I was at it, I replaced every other solderless connector in the dash. It was a little work but now I don't have to jiggle wires to get accessories to work.

Since your boat is a 1989, corrosion has had time to affect the solderless connectors.

I had same problem. Turned out it was corrosion on the solderless (crimp style) connector on the hot wire at the ignition switch. I think as engine speed increases, more current goes from the switch to the electronic ignition. If there is any resistance (from a corroded connector), it results in a voltage drop.

I solved the problem by replacing the solderless connectors at the ignition switch with solder connectors. While I was at it, I replaced every other solderless connector in the dash. It was a little work but now I don't have to jiggle wires to get accessories to work.

Since your boat is a 1989, corrosion has had time to affect the solderless connectors.

check for carosion at the plug in wiring harnes from the dash and the motor conection.give them the wigly test while runing and observe the volt gauge and see if it jumps around . a word of caution on the round conecters with the hose clamps around them ,DO NOT over thighten will cause all sorts of wierd problems.the conection sould be on the motor