Rocker Switch Illumination
Rocker Switch Illumination
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When I replaced my very badly faded twenty year old rocker switches I found the new ones (from C.Cars) were, perhaps unsurprisingly, not quite of the same quality as the originals .
The only real problem though was that the new fog lamp switch didn't have the original tell-tale amber window on top which lit up when the rocker was down. The standard wiring simply drives the bulb from the sidelight circuit, and leaving it like this (i.e with no warning function) would be an MoT failure should an inspector be so inclined...
When getting ready to rewire the switch I got to thinking that I'd never been very impressed with the way the switch illumination is configured on a Seven. Too many switches are already dark by default, and the ones that are 'always' on are too bright and indistinguishable from warning conditions on the others.
It seemed reasonable to illuminate all the rockers at a dimmer level when the sidelights are on, and only use full brightness for warning tell-tales.
The wiper, washer, and heater fan don't need warnings since it's quite obvious when they're on. A 300 ohm resistor wired in series with the bulb reduces the brightness to a suitable level. e.g.:-
Switches that do need warnings are those for the heated screen, hazard warning, and fog light. Each uses two diodes to maintain separation between the controlled circuit and the sidelights. These diodes drop the voltages slightly so the resistor is reduced to 270 ohms to achieve a comparable 'dimmed' level to the other switches. (When the bulb is at full 'warning' brightness the small diode drop from full supply voltage isn't noticeable.) e.g.:-
The brake fluid level test/warning was a little more complicated :-
In the original configuration the bulb is connected to the instrument +ve supply and either the reservoir switch or the test switch shorts the other side to ground to illuminate it.
In the circuit above the relay is energised when the sidelights are on and connects the resistor to ground in parallel with the switches, resulting in the dimmed illumination. Either switch shorts out the resistor to light the bulb at full brightness. An earlier version where the bulb would only light with the ignition on didn't feel entirely satisfactory, so the diodes were added so the bulb comes on with the sidelights even if the ignition is off...
All the extra components were soldered onto small bits of stripboard fitted with a miniature connector, covered in heatshrink, and cable tied to the wiring behind each switch. (The relay used is very small - only 10x7x9mm.)
The bulb in the lighting switch itself is an odd one out. I wasn't sure whether to dim it with the others, but eventually decided it was a 'warning' and left it at full brightness so it remains clearly visible in daylight.
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