Originally Posted by ah-kay

Don't.

You probably will burn the 240D fuse even if there is no problem with the W124 GP circuit. Fuse in 240D is rated for 4 GP, the W124 300D is rated for 6 GP. If the fuse is burning EVERY time then you have a short. GP will NOT normally shortout when it burnt out, it will be open circuit. I will do this test, pull the big connector inside the GP replay and see whether the fuse blow. If it does ( which I doubt ) then the problem is elsewhere and is serious. If it does not then it is one of the GP wires is short to chassis. You can measure the resistance from the big socket pins to chassis. Measure the 6 pins to chassis. You need an accurate meter as the resistance between a short to chassis ( should be 0 ohm ) and GP resistance is about 2-5 ohms.