ettl cable problems

good day all. ive just recieved an Interfit Strobies TTL cord (along with some other strobist fun stuff) to use with my 30D and 430ex. Now i dont know if its because im being stupid, but sometimes when i plug everything in it doesnt work, other times the flash lcd shows ttl and has limited function ie no high speed sync. and finally sometimes its perfect, flash says ettl and everything works. does it sound like my cable might be broken? i would've thought that it either works all the time or not at all so that makes me think maybe i keep making stupid mistakes. anyone else used one of these strobies ttl cords? i also got the strobies isync 4 flash trigger so if anyone has a word to say about those feel free.

if the ground on the cable connecting the flash to the body is not connected well, that falt will cause your camera to not see the flash unit.

i had a similar issue with an old canon ettl cable, i had to take it apart and reconnect the ground.

otherwise, the cable is pretty much a straight through cable, there may be a resister or capicitor or two depending on the design, but the cable itself is nothing special, it simply connects the dots on the flash shoe to the bumps on the flash unit.