Airhead Idiot Light Repair

Not really Amateur Radio related, but recently the turn signal idiot light on the 1974 R90/6 sidecar rig went intermittent and then failed.  I opened up the instrument housing hoping that it was just a bulb but found that the problem was corrosion at the bulb connection.

BMW used a printed circuit board-like material to connect the various lamps within the instrument housing.  I guess it was a good/cheap engineering solution at the time, but after 38 years, it's now problematic.

The issue is with the thin strips of copper foil that make the connections to the bulb holders.  Corrosion ate through one of the strips.  A new replacement assembly is NLA, so I decided to repair it.

Here are images of new and used with the copper 'tabs' visible.  The bulb holders plug into the rectangular holes, contacting the foil tabs on each side.

With the bulb holder in place, a VOM revealed that the problem was only on one side.  A foil tab was missing (the bottom hole, right- side in these views).


My solution was to first carefully clean the metal tab on the right side of the bulb holder.  Then I carefully lifted the top plastic film away from the copper portion of the flexible printed circuit and carefully cleaned a spot on the remaining portion of the broken copper foil.

Using a tiny soldering iron and high-quality rosin-core solder I connected a very small piece of stranded hookup wire between the two.

Problem solved.  And the holder can still be removed for bulb replacement.

If you need to try this repair, here are several thoughts:

If you are not pretty darn good at electronic soldering, I would get everything ready and take it to an expert.  Also, removing the bulb holder assembly and holding it up to a light makes circuit tracing much easier.  The wire I used was from a scrap piece of LAN cable.

Nick - WB5BKL