Re: 39 120 dash instrument lighting

Posted by HH56 On 2019/11/9 20:56:49

It sounds as if the circuit breaker or as Packard called it, a thermostatic relay, built into the headlight switch is operating. Typically the CB or relay will operate and self reset at a frequency depending on how bad an overload might be. Question would be what other lights are on when this is happening.

If the wiring is stock the instrument light rheostat is fed from the headlight switch along with other lights. Wiring diagrams show there should be an inline fuse in the wire from the headlight switch that feeds the instrument light switch. If there was a problem with the instrument lights that fuse should blow first and the CB would never get a chance to operate. When the headlight or other wiring has a problem or old age or a bad adjustment has changed the capacity of the CB to a lower value that is typically when it operates.

If there is no fuse protecting the instrument switch on your car, one common issue with the old wiring and the single wire sockets the instrument bulbs use is the insulation shrinks back or cracks and allows a bare portion of the wire to contact the grounded metal shell of the bulb socket where the wire exits the hole at the back of the socket.