How do u test glow plugs?

Disconnect the glow plugs, put the clamp end of a test light to battery + and touch the spade tip of each plug with the test light. Open ones won't light, ones with high resistance will be dim.

Ok i replaced some of the bad glow plugs and still hard starting cold and hot what is up ?
It is a 97 gmc 2500 4x4 5 spd
Thanks for the info

Ok i am also experiencing lack of power and jerky shifting.
It has a new lift pump that is working, new fuel filter. Oil change today.

Also the constant power to the radio and power locks is not working which is leading me to electrical problems.

HELP!!!!!!!!!!!!!!!!!!!

Flanman, where are you? You need to take this thing to a garage man, or break down your problems one at a time? This thread was about glowplugs, now you've got all kinds of problems!

The first thing you do to these beasts if you suspect electrical problems is clean all the grounds. Two grounds to batteries, two connected to the lower intake (one on each side), and one braided cable between the frame, block and firewall near the starter.

Ok thanks i will try that.