how to check a glow plug?

[Trench_rat]

i have had some issues cold starting my surf , i suspect possibly the glow plugs are the problem as its getting plenty of fuel and starts wells and runs good if the engine is already warm , i pulled one out tonight and gave it a clean up then i rigged it up to a battery and it stayed stone cold , does this mean that they are shagged?

[LOLYF]

Sounds like it. The tip should glow red hot pretty quickly if its working and hooked up right.
I've just replaced mine in my surf, one was completely dead the other three were ok but cheap enough to do all four.