I'm looking at 98 S10 headlamp wiring. The low-beam ground wires are yellow for both left and right. If your new relay provides a ground for these lamps you would want to connect to yellow wire.
The ground wire for high-beam lamps is purple. There's one green/white wire but this is for the +12 side and you would not want to connect a ground to this wire.
You might try connecting the "magic-box" green wire to the high-beam purple wires and check results.
BTW ... left and right side headlamps are fused at 10 amps. Do the instructions suggest replacing 10 amp fuse with something larger since you'll require more current to power low and high at same time?
Routing and terminatin the wires:
RED wire: 1 route the red wite to the battery junction block`
2 remove the 17mm nut from the power distribution stud
3 slip the ring on the RED wire over the power distribution stud and replace the 17mm nut
GREEN/WHITE wire: 1 route the GRN/WHT wire going to the high beam bulb
2 using a pair of pliers, crimp a t-tap to the green/white wire
3 plug the tab on the end of the GRN/WHT wire (from relay) into the t-tap
YELLOW wire: 1 locate the YELLOW wire going to the low beam bulb
2 using a pair of pliers, crimp a t-tap to the YELLOW wire
3 plug the tab on the end of the YELLOW wire (from relay) into the t-tap
then just says test for correct operation... and when i try the high beams BAM there blows the fuse... its a 20 amp fuse we tried a 25 and same thing