Wiring Question

[Belltone85]

I have a 73 with a 340 non A/C car. When the key is turned all the fuses are getting power except for 6,7,8. i believe its number 6 that runs the gauges and the heater because when i put power to that gauge the heater will work and so will the gauges. i looked at the wire on the back of the fuse block and from that fuse there is a tan and a black wire. the black wire goes through the firewall i think, but the tan wire goes to a plug with three round female terminals in it. i have looked all under the dash and i have no idea where this is suppose to be plugged into does anyone know? will this help fix my fuse?

thanks 

[Challenger6pak]

Maybe this will help.

[Bullitt-]

Marbury, #6 = guages #7 = heater #8 = Radio. .  All three of these get power from the ignition switch, therefore on the supply side you need to back trace to the steering column wiring & see that those wires/plugs are intact,(IDd in diag. as Q2A-12BK) then to the ignition switch and back out to the power wires running to the switch (IDd in diag. as J1-12R) . Plug w/ three rounds are for A/C not connected on your model.