Originally Posted by 97 SL320

Are you sure the car is a 90?

There are 2 systems I know about.

If the car has a EZL it should have a single coil and distributor. My 91 300SL M104 3.0-24 Valve has this. The fuel control is Bosch K jet / CIS

If the car has multiple coils, they are triggered by the engine computer. My 97 SL320 M104 ME 2.1 engine control.

I had though the 93 - 96 HFM -SFI had multi coils and used engine computer to trigger the ignition.