Measure the resistance between the steering switch connector terminals 14 to 17 and 15 to 17. Standard

Steering switch | Condition | Resistance Ω
Connector | Terminals
M303 | 14 | 17 | START / STOP switch ON | 1982 – 2063
switch ON | 708 – 737
SEEK DOWN switch ON | 314 – 327
SEEK UP switch ON | 118 – 123
SOURCE switch ON | 1Ω or less
15 | MRK switch ON | 708 – 737
switch ON | 314 – 327
VOL UP switch ON | 118 – 123
VOL DOWN switch ON | 1Ω or less