The Adapter will also. Lose the cables, Not the Fun. A constant blinking status light indicates a successful link. and inconsistent, faster blinking status light indicates a poor link. Try Moving closer to the other player(s) to improve signal strength.
While the product itself is a great basic idea, it JUST DOESN'T WORK!
I won't ask for a refund, but I will advise not to bother buying this. (You're better off buying a 3rd party wired multiplayer adapter for GBA devices, that is longer than the official 1st party wired multiplayer adapter for the GBA!)
Besides; if I wanted wireless multiplayer or co-op on the GBA? I'll just stick with the 1st party adapter; at least I know THAT works! (Despite the fact that it doesn't support that many video games for that platform!)