The connections of the HL2+ Key jack are:
Tip = Dot, Ring = Dash, Sleeve = Ground
When it is desired to use the HL2+ Key jack for a straight key or external keyer, in Thetis for HL2:
1. Deselect Iambic option in Settings > DSP > CW. This puts the HL2+ keyer in "Electronic Bug" mode where Tip is Dot and will produce a string of dots for as long as Tip is grounded. Ring is as a straight key and will produce CW for as long as Ring is grounded, as a bug would.
2. Select "Reverse Paddles". Now Tip is as a straight key and will produce CW for as long as Tip is grounded. Ring is Dot and will produce a string of Dots for as long as it is grounded. Ring would not be used (and must not be grounded) when using a straight key, a Winkey, or any external keyer.
Below is a link to an adapter cable which can be used to implement the connections required above. Those being separating Ring and Tip connections into two, mono jacks. Only the Tip jack would be connected, Ring would not be used.
3.5mm TRS Plug to 2) 3.5mm TS Jack Adapter Cable
The settings and adapter are needed when using a straight key or external keyer with the HL2+ because of it's internal keyer.