I purchased a '74 240D with non functioning gorilla knob system. (The PO had taken a hammer to the dash in anger when the steering lock locked while driving- I know - it did not fix the problem. But it allowed me to get a car with excellent tires, a great motor and manual trans for $200.)

The car was trailered home. In an effort to see if the motor even ran, I used one large battery and 3 jumpers. I disconnected the gorilla knob feed to the glow plugs, grounded the battery to the car, then jumped 12v to the high side of the glow plugs. I counted to 10, disconnected the feed to the glow plugs, then jumped 12v to the starter. With a spark and a click, it was running perfectly. The dash salt shaker glow plug is in series, I think, with the motor's 4, so don't connect for long, or perhaps one of the engine plugs will melt.

If your car starts easily with this, I suggest you check the dash salt shaker. You can get to it easily by pulling out the instruments. Make sure it get's 12v on the high side, that it is not open, and that you have 12v at the gorilla knob switch (high side). One of those parts is probably bad, the dash glow plug or the switch. I'd buy used for replacement, those parts are usually reliable.

'Hope this helps, Ron

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1971 220D, daily driver, new paint, 142K
1973 220D, low compression
1975 300D, back on the road! 166K
1971 220D, salvage, rear hit, engine excellent
1972 250, bad cam, but runs!
1971 230, engine stuck
1971 220D, low compression, rusty
1976 240D, salvage, engine excellent
1966 230SL, water in oil after rebuild