Instrument cluster/hevac lights

[AJV]

Any tips? Instrument cluster and hevac lights are out. Sidelights and lights work (assume switch is ok). Dimmer stalk was all working prior.

The hevac lcd backlight was the first to go (lcd fine). It emits a buzzing noise when I switch the lights on.

Have checked the connections at the kick panel, behind the binnacle and at the becm and cant see any obvious signs of damage or corossion...still gave the a squirt of contact cleaner with no change in behaviour. Any tips on where to proceed? I have rave but am not handy with wiring. Thanks!

[prelude]

Like everything in the P38, the lights are not just powered by 12volts with an analog dimmer in between :)

On connector C242 there are two wires that carry a "square wave signal (pulse width modulated) average value will vary depending on illumination level"

In other words, on the other end there is a dimmer circuit that takes the PWM modulation signal and turns it into a value, or, the lights are simply switched very often and thus the longer the gaps in the switching, the lower the output. The sound you hear would/could correspond to the PWM signal that is created. If you have a scope you could measure the output on those two pins and see what's going on. Try adjusting the dimmer up and down to see of the PWM signal changes for starters.

Cheers,
-P

PS it's pins 6 and 20 on that connector. (in and out)