cdavis03

So My '78 has some issues with some of the lights. My parking brake light/high beam light/gauge cluster lights/seatbelt lights all work but the lights for the speedometer/tach dont work and the turn signal indicator and the interior lights like the feet lights and the light above ne dont work either. Could it just be a bulb for the speedo/tach since the guage cluster lights work? Do any of these lights have to do with eachother? If anyone has any idea please let me know! Thanks!

SwampeastMike

Both the cluster and gauge pack have flexible printed circuits that a well known for problems. The layers of the circuits come apart and the traces short out.

The background (gauge) lighting is all in one circuit--the the hot is a grey wire coming from the headlamp switch. The warning lights and gauges themselves get power (and ground) from various circuits. The printed circuits are the common items among them.

The interior courtesy lighting is completely separate from the gauges and background lighting. The courtesy delay module is a common trouble spot.

Fortunately for you the '78 dash is easy to work on compared to what came before. Sounds to me as if it's time for you to remove the cluster and gauge pack (at a minimum) and look for problems as you replace ALL of the lamps.