1977 -78 Gauge questions

[kennyw]

That is the correct housing for the electric oil gauge. I would hook it up to a sender and test if it works.

GM did some little changes like this as a rolling update during the middle of a production year, so maybe you have a late 77 build and they switched to electric oil by the time your truck was assembled. But it is also just as likely a PO switched something out in the last 40 years as well.