There are electrical grounds literally
everywhere on these cars. Each and every system will have it's own ground, some more than one.
The tail/brake light grounds are on the rear bumper support, and/or on the driver side frame rail at the rear.
The gauges are also separately grounded thru the circuit board, and several grounds in/around the radio mount behind the cluster.
The main ground from the battery is just under the driver seat, to the chassis. Then, there is a large cable from the frame, to the passenger side engine mount area.
Check thse first, and see that they are
clean and tight.
Welcome to C3VR, btw!
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Joel Adams
C3VR Lifetime Member #56
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"