BMW 525 tds

I have a 1994 525 tds, E34 with M51 engine. Recent unreliable starter solenoid operation has deteriorated to complete failure to operate from the key. I have attached a bypass lead from the ignition switch to the solenoid resulting in instant starts every time. I have been told there is a relay in this circuit, can anybody tell me where it is? I have searched all the boxes I can find for the black/yellow lead from the switch to the solenoid without success.

I have a similar problem, 1994 525tds Touring. Seems to respond to hitting the starter motor with a hammer, a click results. However the solenoid will engage sometimes but not turn the engine, no current drawn either. Really need to take off the whole thing and investigate. Let me know if you have found the answer.