Antenna for ST 6001+ Autopilot

[Mark - Raymarine - Moderator]

Hello Mphem,
Your S3G autopilot doesn't need a GPS antenna to function, just as your C140W doesn't need an Autopilot to function. They both can work independently of one an another.
As you have already pointed out, the C140W has an internal GPS antenna. In some cases, depending on the location of the MFD individuals would install an external GPS and wire it to the MFD for better satellite acquisition. If your C140W's internal GPS antenna is set to "ON" and is working just fine, then an external antenna is not being utilized / needed, but perhaps for redundancy. Unfortunately, I can only speculate on what the rail mounted GPS is for as we do not know where the GPS wire terminates nor the model number of said GPS.