T5s come on for 3 seconds then off
 

Does that mean the ballast is done?

Agrr :(

check to see if your endcaps are tight, check your bulb ends to make sure your getting a good connection. What kind of light? Have you used contact cleaner on the endcaps?

Check the end connections,what has worked in the past for me was taking the bulbs out then putting them back in. May work,may not worth a try though.

Give us more info on the fixture, dual lamp, more? Many dual lamp configurations running on a single ballast will do this if one of the lamps is weak or on the way out. It's the EOL or 'end of life' safety feature of many of the newer T5 ballasts. The ballast will sense one of the lamps is at the end of its life and turn both off after a couple of seconds.

Try a new set of lamps before you get too concerned over a possible problem with the ballast. It's an easy way to narrow down the problem.

Sounds like your ballast is shot.

More than likely the ballast. Could be the bulb too, did you try other bulbs?

Possibility of it being a solder connection or ground too

Long story short i got my end caps wet and they did the same thing. I waited till the where dry and it fired right up.

It seems like they got wet and I think some salt got in there. I remove the bulbs put them back in and it works fine. However it happens everyday now. Tried cleaning everything out of the end caps but its a nuisance now. Everyday I have to remove the bulbs and put them back in to get it to work.

Its a Tek light fixture 36" x4

happens sometimes to T5's most likely loose wiring.

Get some electronic contact cleaner from canadian tire. Spray liberally and should solve you problem. Or you can just replace the endcaps.

Ken