Bench testing glow plugs

Q. G’day, can you tell me the process for bench-testing glow-plugs? My 2.8TD GQ was getting pretty hard to start over the recent months, so I got online and bought a set of glow-plugs from eBay. I swapped them in okay, but it doesn’t seem like they’ve made any difference. It still takes a lot of cranking to start on cold mornings. I want to know if it’s the glow-plugs or something else that’s causing the hard starting, before I pull the plugs out and send them back for replacements.

A. Step 1- make sure the glow-plugs you have are the right ones. Even the ones in the vehicle currently may be the wrong voltage.
Step 2- check that you have voltage to the electrical bar connecting the glow-plugs when you turn on the ignition. To ‘bench test’ you can put each one in a vice and connect Battery Negative to the Vice and Battery Positive to the threaded end with the little nut. This is the Positive end. Let’s say no more than 3-5 seconds the plug should be getting ‘red and hot’ so be careful.
Step 3- Consider when this started; all of a suddenly or gradually became and issue. It may be an ‘old age’ compression issue or even the injectors and pump may need some work.
Last thing- If all comes up OK sometimes then you can just try to ‘double glow’ the system. Meaning when the glow plug light goes out turn the ignition off, wait 3 seconds and turn it back on for a 2nd glow cycle before starting.