I've got a 91 740 NA with 180k miles on it.

Over the past two weeks, I've noticed some different things going on with my car: first, it will occasionally take a couple tries to start. You turn the key, it turns over, but it just might not start. Maybe it takes two tries, maybe it takes ten.

Other times, it starts right away with no hesitation.

And today, for the first time, I turned the ignition to get absolutely no response whatsoever - no dash lights, nothing. So I pulled my other car over to jump it, when on a whim I tried the ignition again - it started right away. Ten minutes later I cleaned the battery terminals (which were already clean anyway) and double-checked the cable tightness. Decided to start the car and it took two or three tries before starting a little shaky. Once it started, the idle was fine, but a couple times when I revved it it was a little rough.

Once the car is started and I'm driving it, I notice no symptoms at all as far as driveability goes.

A few more things that might either clarify or further muddy the situation:
- I recently discovered the car is about 10,000 miles overdue for a timing belt. I now have the belt and tensioner on hand, but need to install them.
- the SRS light has come on recently, and it stays on (not intermittent). Very, very occasionally I will notice one of my dash gauges (RPM or engine temp., may have happened once with the speedometer) flicker up and back to place.
- the battery itself is less than a year old, but the previous one had a bad cell and contributed to weird issues, too. The battery hold down on the car has basically disintegrated - has this created another shifty battery situation?

 

Problem potentially solved - while the clamps were tight on the battery, the alternator cable attached to the positive terminal was itself loose from the connector. Cleaned and reclamped - we'll see.

 

It is sounding more like the ignition switch is going bad. The electrical portion of the switch is screwed onto the rear of the key switch. When the contacts wear you have similar problems that you speak of. I doubt that the alternator wire is the problem.

 

I think Jag is right, you described the exact same problem my 1991 240 had last week. Would turn over fine one day and then the next, nothing. One time it half kicked over and was on then died. Replaced the ignition switch and bam! Perfect every time.