'84 firebird - fuel gauge reads full most of the time until less than 1/4-1/2 tank then it drops, voltmeter gauge reads ~18V but DVOM check shows 13.5-14V, oil pressure gauge reads high too (goes past 80 when revving engine. I'm thinking that there's a common problem (ground wire?) causing all of these gauges to read screwy. Am I on the right track or is there something else I should look for? Thanks.