Blowing interior lights fuse.

Hi,
My 87 328 blows the fuse which powers the interior light (between the sun visors), which is also connected to the door switches and supplies power to the door handle lighting and the red lights on the rearward facing part of the doors. Only happens after the car has been washed or rained on. I suspect the switches which actuate the interior light when you open the doors. Anyone have some other suggestions?

Thanks

 

Well, you have some good clues. Washing / rain means water is getting somewhere.
Fuses are protection against excessive current, and current to ground without
a good resistive load (light bulb) are bad, and the fuse won't like them. So
I would suggest looking for water paths where water and wires meet. SOMEWHERE
you have a skinned wire that gets wet and establishes a path for 12vdc to ground.
I know - vague. But that's undoubtedly what is causing the fuse to blow after
washing. A fuse is only an indicator, never the 'problem' - they are there to
prevent mass current draw (i.e., fire starter prevention!). Water and electricity
don't mix well - so dig in and find where the wire is scraped, the connector is
exposed to water, a frayed wire with a hairline wire that connects to ground
with water, water in the light itself, water in the light connector, etc. I'm not
trying to be vague - but it's clear that water is completing a path to ground
and causing excessive current flow through the fuse.

Jedi

 

The switches in the doors supply ground to the interior light circuit when the doors are open. When you "short" them to ground by opening a door the lights come on. They're not going to cause a fuse to blow. I would look elsewhere.

 

In order to try to isolate your problem, take out the light bulb near your visor, if now when you try to open the door and the fuse no longer blows then you are looking at the wires supplying the light. (This isn't quite right because you can still supply power to the light without the light being on. This will only isolate a short in ONE of the wires supplying the light.) Try the same for the lights in the doors. You just might get lucky. It beats taking apart the whole doors etc.