Dash lights out, not dimmer or headlight switch

[rigozzi]

Before you go messing with relays and fuses and tearing your whole dash apart, do yourself a favor and check the wiring to the cigarette lighter/aux power port. Cigarette lighter socket may be shorted open too. Any small metal debris that may have fallen into the socket can cause a short a kill the dash lights. Almost everything in the main drivers compartment shares the same common (-).

[BEJinFbk]

Before you go messing with relays and fuses and tearing your whole dash apart, do yourself a favor and check the wiring to the cigarette lighter/aux power port. Cigarette lighter socket may be shorted open too. Any small metal debris that may have fallen into the socket can cause a short a kill the dash lights. Almost everything in the main drivers compartment shares the same common (-).

Just to avoid any confusion, the only thing that the
dash lights and the cigarette lighter circuits share is
accessory overload relay 105. From there, they all
have their own fuses. If something shorts one of
the cigarette lighters, their individual fuses would
blow and not affect the dash lighting.

And “shorted open” is a contradiction in electrical terms.
Shorted refers to something connecting that shouldn’t be and
open means that something that SHOULD be connected isn’t.

Finally, if there was a problem with a shared ground, there
would be more than just the dash lights having problems.
( FWIW, the dash lights have multiple grounding points ).

[rigozzi]

Except that there are two hot wires and one common going to the cigarette lighter. One is 12V to heat the lighter itself, the other is coming from, you guessed it, the instrument cluster and provides the illumination for the cigarette lighter area which is also controlled by.... the dimmer! They share a common which is landed on the cigarette lighter housing, along with the 12V feed which when in closed condition (lighter pushed in) causes a difference of potential (resistance) which heats the coil to light your stoogie. So as stated before, if something shorts out you aux socket, it can also throw out your dash lights because of the shared common and the illumination circuit coming from the instrument cluster/dimmer, typically an arc from the actual event of the short will consequently cause an open circuit, or a component that is shorted open.

[BEJinFbk]

If what you’re saying is true, then whenever
an illuminated cigarette lighter is used,
the dash lights would all go out.