Installed an aftermarket radio in a '96 F-250. Now, the instrument cluster (IC) illumination does not work when headlight are turned on. Interestingly, if the interior dome light is turned on, the IC light works. Anyone know if there are two seperate circuits for the IC lights and/or if a IC light circuit runs through the radio for some reason?

A harness adapter was used when radio was installed, and there are three wires from the adapter that are not connected to the radio (no corresponding wire into radio harness). These are listed below with the corresponding wire in the factory harness:
Illumination --> Orange w/ black stripe
Dimmer - positive --> Grey w/ red stripe
Dimmer - negative --> Black