coil light / heating element light stays on

[StuartTough]

Hi all,

I have a 65 reg B-class Mercedes which has just started a small issue.... The coil light on the dash now stays on, no matter how long the journey.
It used to do the normal cycle of around 3 seconds when turning the key, but a couple of days ago it came ON and has not gone OFF since.

I suspect the glow plugs/heating element have maybe developed a fault, and one or all need replacing?
or
Maybe a relay or something is faulty?

what I need to know is,.....
Has anyone had the same issue and found a quick and easy fix?
also is there a way I can quickly check myself what the issue is before paying a garage to find a fault with (1 plug, for example)

Also, If I change them myself, Is it easy to do and would I need software to turn the light off again? or should it go off automatically once they are changed?

Thanks
StuartTough