Q: check engine light when headlights on.

The best thing to do is read the code that is being output by the ECM and that is causing the check engine light to come on. In 1981, of course, the number of codes output was very limited but whatever the code is will be the starting point of the diagnostic. For example, there may be a code for "system voltage out of range". If so, it could be that with the headlights on, if there is high resistance in the wiring in the headlight circuit, a voltage drop is occurring at the battery or your alternator is weak. To resolve the issue you are having, I recommend that you request a check engine light diagnostic. A certified mechanic from YourMechanic would use a code scanner to retrieve the diagnostic trouble code(s) from your car’s PCM that might have set during the incident and, as well, the Mechanic will assess the relevance of any published TSB’s issued by GM for your car. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.