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[Graham Dunn]

Symptoms:

Left rear, right front and rear running lights are out.
Instrument panel lights (the ones that illuminate your speedometer,
etc) also do not come on when the headlights are turned on.

Headlights, turn indicators, fog lights are all working.

A voltage reading at the right rear light interface (where the bulbs
plug in) shows very low voltages (< 1 volt), The left side has good
voltage readings (~12V).

Does this suggest anything immediately?

Can I narrow down where the fault may lie?

Thanks,
Graham Dunn

[Bob Kegel]

First rule for troubleshooting old BMW electrical systems: check the
grounds. Connections should be clean, bright, and tight. Check the fuse and
relay connections for corrosion. Use a deoxidizing contact cleaner, such as
Wurth Contact-OL or Caig Labs Deoxit. Check the bulb sockets for corrosion.

If this doesn't lead to a fix, get the BMW Electrical Troubleshooting Manual
(ETM) for your model. AVailable on CD from BMW dealers. Paper copies may
show up on auction sites.

[Guest]

I have a 1995 BMW 325i, and my rear brake light kept going out. I kept
changing bulbs, but then realized it was just the connection. I
sprayed Deoxit on it (bought at Radio Shack), and it has worked fine
for months.
-Doug

Bob Kegel wrote:

[Graham Dunn]

Just for the archives, it turned out to be corroded leads on the
headlight switch (which really is quite a clever piece of engineering,
once you get it open).