Check Engine Light 560SL

[shamandog]

Hello:

The check engine light in my '88 560 SL came on a few weeks ago. Car is running fine except for a sligthly rough idle for the first minute when started. I changed the O2 sensor (used a third party) but the light is still on. (Battery was disconnected after changing the sensor)

Any ideas on:

1) What to check next, OR

2) How to read the diagnostic code--the car is 88 so is OBD not OBD2 and I can't find any information/tool for reading the code.

Thanks!

Richard