wiring problems 72 1/2 ton suburban

[borob47]

I just bought a 72 Burb 1/2 ton . 1st. problem .gas gauge goes to full when you turn key on and is way past full with key off .I checked and it has a good ground . Also when you turn the radio on the gas gauge goes to 1/4 tank ? Also tail lights work good when lights are on low beam but go complete off when you turn lights on high . Also no dash lights ?/
Thanks in advance for any help Bob >> ivandale26354@aol.com