If your electrical system
is normal then you will have a feed from the battery(s) to a distribution panel and then individual feeds from the panel to users. The voltage drops will occur in the main feeds (both positive and negative) and the individual feeds (+ & -) You need to determine what the critical volatge is, what and where the various volt drops are.
First, measure the autopilot and seatalk
voltages local to the unit with a DVM between local negative and positive. Ideally, record
the voltages at which the pilot trips into standby. If you have a peak hold DVM use that. Hopefully that will confirm that low voltage reading. A fully charged healthy battery is about 12.5V and you would not want any less than at least 12V in any circumstance of loads during normal sailing
Next, connect a DVM on say 2v range between the battery positive terminal and input to switch panel then between the switch panel and as close as you can get to the autopilot drive supply positive and Seatalk
positive. Ideally, you want to capture the situation which trips the autpilot into standby.
Repeat last for the negative side, battery negative to switch panel negative, switch panel negative to the pilot and then seatalk negative supply.
You can extend the DVM leads if too short with any cable as the DVM draws virtually no current
That should show if there is a problem with undersized cable and other components and hence point to a solution. Failing that, you are looking for transient problems.