Carrying on knocking over electrical gremlins on my JCB 3CX it was the turn of the back light for the dash clock - the bulb was blown and I'd ordered a replacement.
The 'special' bulb for the clock back light arrived - odd little things that have wings that poke through a hole in a printed circuit board, and ramps on the wings tighten the connection - well they do when the ramp has been re-bent !
However back light still not working (though original bulb WAS blown and new one IS OK
) - time for more investigations. Metering the four pole connector on the wiring loom, Ground was where I expected it, 12 volt permanent was there for the clock itself, as was the feed for when the ignition is on, and separately the feed for when the side lights are on for the clock back light. Problem MUST be within the clock module itself.
Time for a bit of brain surgery. Usual 'popping plastic clips' dismantling got me inside. Sure enough as I previously postulated, the feeds from the Ignition and the Side Lights each go straight to their own isolating diode, with their cathodes being commoned and going to one side of the light bulb. I would expect the other side of the bulb to be taken directly to Ground - but no, no sign of any connection to it - certainly none to anything that was accessible.
I should point out that this clock module is a 'sandwich ' of two PCBs separated by riveted and soldered spacers that would be virtually impossible to undo without damaging other bits.
Fortunately I was able to poke a fine tipped soldering iron in between the two PCB's and put a 'salvage link' from a bit of track from the o/c side of the bulb to the rear of the Ground input pin.
. . . let there be light . . . and there was, both with just the side lights, and also with the ignition being on.
Just one more gremlin knocked on the head - getting there
The 'special' bulb for the clock back light arrived - odd little things that have wings that poke through a hole in a printed circuit board, and ramps on the wings tighten the connection - well they do when the ramp has been re-bent !
However back light still not working (though original bulb WAS blown and new one IS OK
Time for a bit of brain surgery. Usual 'popping plastic clips' dismantling got me inside. Sure enough as I previously postulated, the feeds from the Ignition and the Side Lights each go straight to their own isolating diode, with their cathodes being commoned and going to one side of the light bulb. I would expect the other side of the bulb to be taken directly to Ground - but no, no sign of any connection to it - certainly none to anything that was accessible.
I should point out that this clock module is a 'sandwich ' of two PCBs separated by riveted and soldered spacers that would be virtually impossible to undo without damaging other bits.
Fortunately I was able to poke a fine tipped soldering iron in between the two PCB's and put a 'salvage link' from a bit of track from the o/c side of the bulb to the rear of the Ground input pin.
. . . let there be light . . . and there was, both with just the side lights, and also with the ignition being on.
Just one more gremlin knocked on the head - getting there