Checking glow plugs on an upgraded 240D system...?
 

my friend's 240D is having increasingly harder starts, so i thought along with checking some fuel stuff i'd help them check the glow plugs. they have a 1977 240D, initially had the old style glow plugs wired in series. the previous owner upgraded to a system that uses a push button under the dash to manually control the plugs. any initial thoughts on checking their function?

on my 300D i check the GPs at the box on the fender, but i'm guessing the push-button system overrides the relay there?

Procedure to check depends on whether the original loop style plugs were replaced with pencil style. If it's loop style, just look at the squiggly wires between the plugs. They should glow a dull red if energized for a while. If they don't, the plugs aren't getting power or one or more of them are burned out.