Our just purchased 68,70 400 engine with 455 heads& console shifted 350 has an electrical problem.When I turn the headlights on & turn the knob to turn on the dash lights,the gauge goes to discharge every time& the dashlights do not work.I turn the knob back & the gauge goes to charge.I replaced the switch (the old one looked new)but same problem happens.The radio has been replaced with an after market unit before we got it.The car also has a 160 speedo.I don't think this speedo came with this car.Also the neutral safety switch does'nt work.Is it located in the console or on the column? Thanks ahead.

160 speedo was standard on 68's

My experience with electrical is minimal, but first thing I do is check the grounds, and I would also suggest checking the wire that goes from the switch to power the gauge lights to make sure it is not cracked or chafed and shorting out.