The 1978 IRS Form W2 contains Box 16 that reads: "Box 16 Pension Plan coverage? yes/no". I would like to know what the instructions are for that box for that particular year. 1979 would also suffice.

In particular I'm trying to learn if a person was a participant in a defined contribution plan in 1978 would the answer be "Yes". I already assume the answer would be "yes" if the person was covered by a defined benefit plan.

You don't need the instructions (best of luck finding them 20 years later!!). All you need to look at is Reg. 1.219-2. This regulation is effective 1/1/79 and describes the active participant rules for IRA deductions. My recollection is that the "active participant" restriction was first effective when IRAs were introduced by ERISA.

Good luck.