01 Forester L: High beams keep on blowing left hand headlight fuse - help?

M

MikeC

Hello all,

I have an 01 Forester L that I bought a couple of weeks ago. It has
been great so far, and I recently took it on a 1000 mile trip where it
performed fine. But I have a strange problem that started happening in
the last couple of days.

Turning on the high beams instantly blows the LH headlight fuse (a 15A
fuse found in the underhood fuse box). After the fuse blows, both the
high and low beams on the left (driver's) side are significantly
dimmer than they should be. Replacing the fuse is easy and fixes the
brightness problem - at least until I have to go to my high beams
again. I've replaced the fuse three times in the last couple of days.
Oddly enough, this didn't happen at all on my trip last weekend (I
repeatedly switched between high and low on the highway with no
problems at all).

I'm thinking that perhaps there is a short that is causing too much
current draw when high beams are on, but have no idea where to look or
how to start chasing it down (no wiring diagrams on hand). Does anyone
have any suggestions?

One thing that may or may not be related: my outside temp. gauge
doesn't usually give a reading (just "---"); however, I noticed today
that after the fuse blew, I started getting a reading, although an
incorrect one (it was registering as 113F, when it was only about 83F
outside, and the reading didn't seem to change at all - perhaps
getting max signal to the sensor?). I don't know if this sensor is on
the same circuit as the headlamps or has anything to do with my above
problem - I just thought that I'd mention it in case it is, since my
other car (a Saturn) frequently has unrelated items together on one
fuse.

I'd really appreciate any insights/advice from Forester and/or
electrical gurus on this group. I don't have an owner's manual (didn't
come with one), and unfortunately Haynes hasn't made a Forester
tear-down book yet.

Thanks very much,
Mike
(e-mail address removed)
 
Turning on the high beams instantly blows the LH headlight fuse (a 15A
fuse found in the underhood fuse box).

If there were a short in the bulb itself (for the high beam), that would
certainly happen. Try unplugging the bulb and flipping the high beams
on. (Of course they won't come on.) If the fuse still blows, the short
is somewhere in the wiring up through and including the socket into
which the bulb plugs. If the fuse doesn't blow any more, than the short
is in the high beam portion of the bulb itself. You could also check
this with an ohmmeter -- disconnect both right and left sides and
compare the resistances of their high beams. Expect the cold resistance
of the bulb to be much lower than the operating resistance -- filaments
increase in resistance when hot, which is why most bulb burn-outs occur
at turn-on time -- so a low resistance value as measured by the ohmmeter
is to be expected, but if the left side is a lot lower than the right,
you've found the problem.
After the fuse blows, both the
high and low beams on the left (driver's) side are significantly
dimmer than they should be.

How can you tell about the high beam? The low beam is energized by the
daytime running light circuitry (assuming that you have such circuitry
in your country) but the high beam is not. If its fuse burns out, it
should be way significantly dimmer -- just plain turned off!
I'm thinking that perhaps there is a short that is causing too much
current draw when high beams are on, but have no idea where to look or
how to start chasing it down (no wiring diagrams on hand). Does anyone
have any suggestions?

See above.

David
 

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