Need help with Guage problem

[dennisr]

I have aftermarket VDO guages in my 69. I have been having problems such as when I start turning on accessories, the volt meter drops to 10.5 volts. However when I put a tester on the battery, it reads that it is still at 13.8 Volts. The electronic odometer on the speedo has gone blank, but blinks on occasionally. The electronic oil pressure works intermittently. And the led read out on the stereo has gone out. All these gremlins lead me to believe I have a ground problem. I have checked the ground from the engine to the frame, and checked the battery ground. I have also used a set of jumper cables to ground the truck anyway I could think of with no changes. It all seems strange because there are no charging problems and it always starts and runs all accessories just fine. (vintage air and electric fan)

Anyone have a clue what might be causing this?

Thanks in advance,
Dennis