In a 1979 300D (123) there is a black box on the drivers' side under the hood. It contains a strip fuse and the glow-plug relay. Behind the strip fuse and before the relay, mine has 4 pins. the left front is labeled 50 the front right is labeled 31 the back left is 15 and back right is 1A. there are three wires that should be attached to the pins. One is a ground to the body (black), there is a blue wire that goes to the block? or the plugs themselves? and a red wire which goes to the ignition? or vice-versa. Can anyone tell me which wire goes to which pin? I suspect they are hooked up wrong, and I'm afraid to experiment and cause damage. Thanks!