Do you have a GE handset?
if so get the correct cable with the connector that connects to the SX controller and go in and check the settings.

you may want to check the settings in the controller, these are what they should be for this model, ONLY THIS MODEL:
Function: 36v 48v
1 16 16
2 60 60
3 20 27
4 255 255
5 15 15
6
7 80 80
8 255 255
9 35 35
10 255 255
11 0 0
12 0 0
13 113 113
14 24 16
15 36 48
16 130 130
17 135 135
18 149 149
19 255 255
20 255 255
21 30 25
22 183 183
23 50 50
24 100 100
25 0 0
26 5 5
27 0 0
28 0 0
29 0 0
30 0 0
48 30 40
49 0 0
50 0 0
51 80 80
52 30 40
53 18 18
54 0 0
55 0 0
56 20 27
57 35 35
58 30 25
59 0 0
60 15 20
61 70 70
62 60 50
63 0 0

make sure it is set this way.

and please go back and double check your wiring to the line contactor, trace these wires to their origins or destinations and make sure there are no pinched or chaffed wires that could be shorting somewhere on the frame.

I replaced the contactor and PTC. I also swapped controllers with a known good one. The wiring hasn't changed since it ran. It still has code 65. This is a difficult one to troubleshoot.

could be a bad PTC across the line contactor buss (that's the flat capacitor looking device that hooks between the buss bar connections on the line contactor, about the size of a quarter)
may be open, could have a bad connection.

also welded 1A contactor can cause this (if equipt with one)

check for continuity across the open 1A contactor

possible wiring error, insure no device is connected to the load side of the line contactor

worse case scenario is a bad controller unit