This starter is the best solution of the nightmare each owner of a classic bmw.
One of a fastest n easiest form of sorting out the starting process if u search the web enough. The key switch at the barrel is one of the problem. When u acc the key n turn to start, there 8volts current is energized in 0.5 cable to the starter solenoid to make contact to the solenoid to engage the starter motor, the starter motor runs direct from the battery to turn, the solenoid to push the piston inside to engage the flywheel.
Over time, the 8volts signal on the wire goes down n the wire looses its conductivity. Adding on this starter solenoid increases the voltage to energize the solenoid.
A cheap n effective way. Finding the that small wire to change is a tedious job n even I have yet to tackle it.
Best leave it in there n trouble free starting.
Cheers..