I hooked up my shift light but I ran it to the fuse box. Dont do that lol. Im going to redo it when i put my water, oil, and nre reverse glow gauges in. But i would try the wire for the vert top. its right by the ash tray and you can pretty easily just run a wire up behind the radio and up through the clock if thats where you are running it. As for the ground, I just drilled a hole in the big metal tube behind the cluster and grounded it there.
EDIT; For the lighting source pull the cluster and find out which wire on the headlight switch turns hot with the parking lights on.
for your tach splice into the tan/yellow wire exiting coil or at back of stock tach or any point in between and you can connect tach lighting into the headlight switch just probe wires behind the switch with a multimeter to find a wire that has current only when parking lights and headlights are on i believe it will be a brown wire....now your talking about the guage lighting and not a shift light right?
where exactally did you connect tach and light wires were you able to splice behind stock tach or at coil and where did you connect the light... behind switch????