Anahka if you read the wiki you will find my solution to your problem but here is it again

Using /run is a local map ping, if you use /run on your main then your alt's will not be able to grab this.
You need to use /run and /script on your main

Heres the wiki link and the example again:
http://www.dual-boxing.com/wiki/inde...o:Minimap_Ping

Main Charactor
Code:
/cast Spellname
/run Minimap:PingLocation(X, Y)
/script Minimap:PingLocation(X, Y)
Alts
Code:
/cast Spellname
/script Minimap:PingLocation(Minimap:GetPingPosition())
Hope this helps