Instrument Panel Lighting Switch/Rheostat
All Triumph Models
To avoid the potential for overheating of the instrument panel switch/rheostat and possibility of anunder-dash electrical/insulation fire, DO NOT change the bulb wattage specified by the factory and DO NOT wire any additional lamps or devices into the instrument illumination circuit.
With Triumph/Lucas wiring systems, the electrical feed for this instrument lamp circuit is from the fused side of the rear light wiring and is a solid red colour to the panel light switch/rheostat, (this is a ceramic mounted, open wound, variable resistor). The wiring from the switch to the instrument lamps will be red with a white tracer. No additional lamps should be wired into this red/white wire or circuit! It should feed only the instrument lamps as installed by the factory.
Fusing of the rear light circuit with greater amperage than specified, may result in severe overheating of the instrument light switch IF an electrical short occurs between the switch and the lamp(s) with the switch in partial-to-full-dim positions. (Note: it is debatable as to whether the existing specified rear lamp fuse would recognize a short circuit with the switch in partial or full-dim position). Therefore, installation of an accessible low amperage (3A) “inline” fuse on the red or red/white tracer connection at the switch during dash re-wiring or harness/loom replacement, is recommended.
As the instrument panel lights are fed from the “fused” side of the rear lamp circuit, the lack of dash lights may indicate that the vehicle’s rear park/running lights are inoperative. This is a design feature to alert the driver that the rear lights are not operating due to a “blown” fuse.
When night driving, having the instrument light switch at maximum brilliance will produce the least heat from the rheostat and prevent heat degradation of the switch and electrical insulation that may be in close proximity to the switch. Conversely, having the instrument lights dimmed to minimum light level will generate the greatest amount of heat.