I installed an AC Delco sender into my 86. Within a couple of days the battery was dead. I recharged it, drove it and afterward, the battery went dead again within a couple of days. Since the sender was the only thing I did or touched, I disconnected it. The battery has now been holding a charge for several weeks.
Since the orange/black wire is unswitched 12V, there is constant power going to it, and the sending unit grounds through it's base. I tested an 85-87 sending unit and found no continuity between terminals when there is no oil pressure (engine not running). The new 88 sender has continuity at all times through it's terminals.
Rock Auto says the unit isn't warranted since I installed it in an 86 Fiero when it's intended for an 88. If there's nothing wrong with my unit, I don't want to press the issue.