Is the bulb blown?
If you take the bulb out, using a multimeter, do you get a reading? Mostly in the old holders there are 2 point of contact at the base and these are both live. A reading should be taken from ONE of these and either the side of the holder or a good earth. Don't put anything across these as you will blow something. You can also test with an old, working indicator. One wire end on one base and one on the holder side.
Before you test this, is the battery OK? Do the indicators work without the engine running is a good test of this.