Glow plug problem?

Heya,

Recently got myself a 93' 2.8L 4wd Hiace, have a weird little issue I cant seem to figure out, when starting in pre-ignition the coil light will just stay on forever and not go out, it will however start and run perfectly fine and then the light goes out, when the engine is warm the light will only flash on for a second as you'd normally expect,

After around 20 seconds with the key in pre-ignition you hear a click and power to the glow plugs stops (indicated by a circuit testing light touching the plugs), if I wait for this click, turn the key to off and then pre-ignition again and then wait for the click, doing this loop around 5 times, the coil light will eventually turn off and the engine starts fine,

Wondering what might cause this as cant find any information online to explain this? I will hopefully get my hands on a multi-meter soon and give the glow plugs a test, they seem somewhat okay at least as the engine definitely doesn't start with the glow plug rail disconnected, bit reluctant to just replace the plugs as they seem to be quite stiff and don't want to snap them,

This seems to happen regardless of the weather, was happening when it was around 15C and now at around -5C, at the same time I seem to have another issue with a buzzer going off after 8 seconds with the key in pre-ignition, which then turns off once the engine starts, this buzzer seems independent of the coil light being on or off,

Any Advice on this would be fantastic! was hoping to solve without going to a mechanic! Thanks!

No idea about the glow plugs but my buzzer goes off after a while of leaving the key turned in the ignition. I think it's a feature just to tell you it's there and ready to go or that the key is inside the van but all it is is annoying.

It might have something to do with the door being open too or that could be another warning, I can't remember exactly when it happens, just that it does and I've got used to it now.

Cheers, after a wee bit of digging around found that it is the brake warning relay doing the buzzing, strange as it sounds exactly like the buzzer for leaving lights on, cant say I know much about these things is there a reason it is doing this?

Decided to hope changing out the glow plugs would sort that issue as all four came out easily with the engine warm, but still can wait forever and that coil light will not go out until you just crank the engine anyway, feels wrong to do that but at least its starting up fine.

Did manage to get my hands on a multimeter, am getting 12v to the rail so am not too sure, with it all connected up getting 7V on the glow plug tips which is to be expected right with voltage dropping over the resistance from the plugs? hopefully I can decipher the repair manual I just picked up point me in the right direction otherwise its off to someone who knows much more than me!