The other high amp circuit on these earlier engines is the glow plug circuit. While the two cylinder engines may do just fine with a 10GA circuit the three and four cylinder engines can suffer from "slow glow".
A very quick and easy way to fix this is to insert a simple solenoid into the glow plug circuit. To install this solenoid you simply steal power via a 10GA wire from the starter post. Please be sure to fuse this run as close to the starter post as possible.
You then snip the glow plug wire, add ring terminals, and place the glow plug end on the opposite side of the solenoid from the starter wire and the glow plug switch end goes to the "S" terminal.
Now when you hit the glow plug button a the solenoid closes and creates a direct path between the high current, large gauge, starter wires and the glow plugs. All the glow plug switch has to do is energize the solenoid coil which takes very little current. You are no longer running the glow plugs through 20+ feet of 10GA wire.
Most all newer Universal and Westerbeke engines, with glow plugs, utilize a "preheat solenoid".. You can buy one from Blue Sea and save money. Do be sure that it is ignition protection rated.