I have a Brute 750 50# thrust, probably around a '93 model since it's on a '93 boat. 24V, foot control. Speeds 1, 2 and 3 run at the same speed. Speed 4 shuts the motor off. Speed 5 runs at what looks to be normal speed on #5. Changed the rotary speed control switch, still have the same problem. Checked a wiring diagram and everything looks fine. What am I missing? HELP!