When you turn the ignition on do you hear the relay click on then off a while later?
Towards the end of the cycle you should be able to feel some warmth on the end of the GP.
If you have a volt meter, you should get a voltage more than say 8v at each plug when you first turn the ignition on.
The strip fuse is a good place to start if you find things are dead.
I once had a spider find its way into the relay box, it fried & then stopped the contacts working. I cleaned them & all was good.
Gp's are important even in warmer weather as they make it a bit easier on your battery & starter motor.
Good Luck !!
Grumpy Old Diesel Owners Club group maintainer/member
"Life is tough..it's even tougher if you're stupid." John Wayne
I no longer question authority, I annoy authority. More effect, less effort....
1980 300D now parts car 800k miles
1984 300D 400k miles
1987 250td 90k miles English import
2001 jeep turbo diesel
other toys ~J.D.,Cat & GM ~ mainly earth moving