My GPS seems to be lost

Last fall, I removed the Raystar GPS 125 installed in the mizzen mast, in favor of the antenna for my AIS 650.  This spring, I found that I cannot use the AIS 650 for navigation, so I am attempting to install the GPS 125 again, but it refuses to work.
As I read the manual, I should supply + 12VDC to the cable connected to the GPS, ground its green and brown wires to its shield, and watch the GPS boot (red flashing LED), listen (amber flashes) and acquire a fix (green flashes every 2 seconds).  If I wish, I should be able to read the serial data output on its yellow wire, measured with respect to the ground.
What happens is more subtle. When I apply power, sometimes the LED flashes red, sometimes it does not.  Often the LED stays stubbornly off.  I have removed all other connections to the unit, but I can't seem to get it to operate consistently.
Apparently I cannot buy a direct replacement for the Raystar 125 from Raymarine.  They now sell the Raystar 130, which has no NMEA 0183 output, favoring instead their proprietary Seatalk (ng) bus.  Using this GPS would require at least one adapter, from Seatalk (ng) to Seatalk (1), and then some arrangemet to convert its data from Seatalk (1) to NMEA 0183.
I understand that Garmin still sells a GPS that uses the NMEA interface.  I hate to add another brand to my boat, but it seems that this may be the path of least complication in the short run.
On the other hand, the Seatalk (ng) bus is a lovely adaptation of the NMEA 2000 "standard", implementing a nice moisture-resistant version of a CANnet.  Its topology is backbone-and-drop; it has fairly wide bandwidth, and its operation is largely independent of any particular unit.  Unfortunately, very little of my electronics could be reused.