Campbell Scientific SP10, SP10R, SP20, & SP20R Solar Panels - Manual (Page 15)

Appendix A. Solar Panel Connector
The SP10 and SP20 solar panels are shipped with the two lead wires stripped
and tinned. A barrel connector (pn 788) connector must be attached to use an
SP10 or SP20 with the 21XL.
With the connector, the cable can be inserted directly into the 21XL Charging
Port on the side of the micrologger.
If it is necessary to solder the connector on the cable, please refer to the
diagram below.
pn 788
FIGURE A-1. Connector wiring
A-1