I had found an excellent little LUA script here: http://www.esp8266.com/viewtopic.php?f=19&t=1049#p6198 the user goes by the name "gwizz". Kudos to him (firstname.lastname@example.org)
dofile("i2c-autoscan.lua") Scanning all pins for I2C Bus device Device found at address 0x3C Device is wired: SDA to GPIO0 - IO index 3 Device is wired: SCL to GPIO2 - IO index 4 >
This works a treat and helps me to avoid silly mistakes. - Highly recommended.