In article , Sailor wrote:
Have the same ST60 system. I added a 3000uf, 60VDC power supply
filter cap to the positive
side close to the instruments, never had a problem. Also make sure
you've installed the ferrite
filters on the lines from the depth transducer and also the power
supply.

If it works fine. I was going to suggest also a diode, but thats going to drop things .5 volt
or so. 3000 uF is wimpy but small in physical size but larger uF could be a problem with on switches.

greg