Our BMW Bavaria exhibited the symptoms of a faulty solenoid on the starter. The battery was fully charged and I re-tightened the positive battery cable connection on the solenoid. Turning the key didn’t produce a click out of the starter. After I tapped the solenoid with a breaker bar; the starter cranked and worked normally.
I used the Bosch Vehicle Part Finder, which specified a SR71X Remanufactured Starter. I ordered it from my local NAPA store ($109 USD).
I wasn’t looking forward to removing the old starter, though it turned out to be easy. I managed to remove the two bolts holding the starter to the block using only the box end of a straight 17mm combination wrench. A 17mm half-moon wrench would have made it a little easier.
The smaller diameter of the new starter made it simple to use a socket wrench to reach the bolts when I installed it. It took about 5 minutes. The car started on the first turn of the key. The next turn of the key did nothing.
I removed the steering column cover and looked at the ignition switch. The half of the switch soldered to the wiring harness was falling out of the steering wheel lock housing, leaving about 5mm between contacts that needed to touch.
In retrospect, I probably could have repaired the old switch, had I seen two of the parts that fell into the bottom dashboard cover. Since I’m apparently on a replace 36 year-old car parts jag, I ordered a new switch from Mesa Performance. The switch is actually an E21 part (61 31 1 358 932), about $100 USD. They told me it was cheaper for them to buy a complete E21 switch and sell me just part I needed rather than buying an E3 ignition switch.
I had to reuse the Molex connector from the old switch and grind off an alignment pin on the new switch.
After I installed everything, the car still wouldn’t crank. I measured 12v+ on terminal 50 on the solenoid when I turned the switch to start, but it just clicked. Then I shorted the cable from the battery to the motor windings connection on the solenoid and the starter motor didn’t turn.
I took the starter back to NAPA and it tested OK. Frustration escalated. The starter motor wasn’t getting enough current – I measured the voltage and it was OK. Before reinstalling it again, I used a wire brush around the starter opening on the block to remove the surface rust. Then I removed and cleaned the ground strap between the block and the frame. As a precaution, I also replaced the positive battery cable; the old one seemed a little too flexible in the middle for 4 gauge copper wire.
When I put it back together and tried it, it cranked, ran for a few seconds and shut off. I tried this several times because it seemed like the fuel bowls in the carburetors were empty. There was smoke coming from the resistor next to the distributor. In the wiring diagram, the second small wire went from the solenoid to 12v+ on the ignition coil. I disconnected that wire from the solenoid and everything worked normally.