I have a '91 325IX and a '88 M3, both on BMW OEM trickle chargers. Last week I pulled the battery from my M3 and dropped it into my IX because of some battery issues. The IX started right up and I later learned that the IX's battery was dead (on a trickle charger...what's up with that?). So, I bought a new one, put it in the IX and returned the borrowed battery to the M3. Mean time, the trickle charger remained connected during the period of time the M3's battery was missing.

Now, a couple of days later I try to start the M3 for the first time since the battery swap. It cranks like a champ, but won't ignite.

Could I have done something wrong by leaving the trickle charger connected when the battery was missing?

All fuses look good. I'm in the process of determining if I have fuel or spark. I have an induction timing light I can clamp over an ignition wire to see if it's sparking, but I can't find a positive terminal in the engine bay to power the light. Could I hook it to the positive lead on the starter?

I'll pull a plug to see if it's wet. That means I'm getting fuel. Any other thoughts?