[V8] Intermittent no-start and rotten egg smell

[Radek]

After installing a new air filter and cleaning the spark plugs, I tried to start the newly acquired 93.  It wouldn't.  The fuel pump relay would click once, engine would not turn over.  There seemed to be no current draw (I tried starting it with an interior lamp on, it wouldn't fade).  PO had an aftermarket radio installed and left some cables connected to the vacum pump next to the battery, which I removed.  I reconnected those and tried again - the car started.

It ran at high idle, about 2000 rpm, dropped to 1000 rpm when in Drive.  I will check the TPS tomorrow.  At some point it gave a nasty smell of rotten eggs - where's that coming from?

I let it run until it warmed up and switched it off.  Came back ten minutes later, without disconnecting anything - it wouldn't start.  Same symptoms:  when the key is turned, fuel pump relay clicks, no voltage drops, engine doesn't turn over.  Giving it a boost with a 60A charger doesn't help.  
Where should I look?

Radek
91 V8Q 5-sp
93 V8Q