amdx said:
My daughters 97 Avalon blows the brake light fuse about every other
day.
Googling finds wiring diagrams at
http://autolib.diakom.ru/CAR/Toyota/1997/Avalon/SYSTEM WIRING DIAGRAMS/12053.pdf
and
http://autolib.diakom.ru/CAR/Toyota/1997/Avalon/SYSTEM WIRING DIAGRAMS/12078.pdf
; not sure if those are exactly the right ones for your car but maybe
they help. There are more at
http://autolib.diakom.ru/CAR/Toyota/1997/Avalon/SYSTEM WIRING DIAGRAMS/
..
Both diagrams show that the stop fuse should be 10 A. There should
also be a sticker inside the fuse box (or lid of the fuse box) with the
correct fuse ratings.
General advice: In my experience, the problem is more likely to be in a
switch, lamp socket, or connector, rather than the wire itself. If it
*is* in the wire, it's often near the end of the wire (where it is more
exposed to moving parts, humans, etc) rather than buried in the middle
of the harness somewhere.
Is there anything internal to the brake lights that could short to
cause the fuse to blow?
If the lamp socket is really mangled, it's possible for the "hot"
contact to touch the "ground" contact. You can usually tell by taking
out the lamp and looking down into the socket.
It's even possible, but really rare, for something to be rattling around
inside the bulb (like a piece of a filament support), but I mention it
because it's usually really easy to check - just take out the lamp, hold
it up to the light, turn it this way and that and maybe thump it with
your fingers.
You might check the lamps to make sure that the right part number is in
there. The owner's manual and/or website of the friendly local auto
parts store should help. It should be relatively difficult for somebody
to install lamps of such high power that they blow the fuse, but it's
pretty simple to check.
A single rear brake lamp should draw about 2 to 2.5 A depending on the
exact part number. The third brake lamp will be less than this,
probably closer to 1 A. This gives a minimum of about 5 to 6 A; if
somebody has installed a 5 A fuse for the brake lights, you have just
found the problem.
Some rear lamp clusters have a short harness (like 8 inches or 20 cm)
that goes from all of the lamp sockets on the cluster to a single
connector with maybe 6 pins; this is for ease of assembly and
replacement. Often this harness is zip-tied or otherwise fastened to
the back of the cluster; maybe the zip tie cut the wires and shorted
the brake light wire to ground.
Sometimes cargo in the trunk can cut the rear light wires, especially
if the trunk lining is gone or out of place.
If this car has or ever had a trailer hitch on it, check the trailer
wiring, or the remains of it. Often this is not properly routed and
sometimes get pinched against the body. Or, if it had a hitch that
was later removed, sometimes people just let the wires dangle down
behind the rear bumper. If it doesn't have a hitch now, get a good
light and look under the back of the car, towards the bumper, for non-
factory-looking holes, or cuts in the bumper cover, where a hitch
might have gone. Also look at the rear lamp clusters from the trunk
to see if there are any non-factory-looking splices.
Check the third brake light as well; it's on the same circuit. Usually
its wire runs on the bottom side of the rear parcel shelf, in the trunk,
from the light over to one side of the car. The owner's manual should
tell you how to get the lamp out of it, which will let you inspect the
lamp and socket.
You might look at the brake light switch, which is mounted to a bracket
near the brake pedal arm; it's above your toes if you're stepping on
the brake. Usually it's not too hard to at least get your eyeballs on
it, even if working on it is more entertaining. Usually when these
fail, the plastic switch body cracks and the brake lights just stop
working. Sometimes the driver catches the wires to the brake light
switch with the toe of his or her shoe and pulls them around, which
might make them short out on the brake light switch bracket or other
nearby metal.
The wiring diagram linked above shows a "light failure fixture" which
lives on the left rear lamp cluster. This monitors the current to the
brake and tail lights and turns on a "lamp failed" indicator on the dash
if anything isn't drawing enough current. This could conceivably be
screwing up and shorting the brake light wire to ground. If it's not
obviously mechanically beat up, I would assume it's OK on the first
pass. If you start to suspect it, the test is probably to bypass it and
see if it stops blowing fuses. The bypass would be to unplug it and
splice the green-white (brake feed), green-red (regular brake lights),
and green-orange (third brake light) wires together; and separately
splice the green (tail feed) and light green (tail lights) wires
together. The other three wires can be left open. If you bypass it,
the "lamp failed" indicator on the dash won't work anymore.
There is at least one other circuit run by that fuse, there is a shift
lever release (solenoid?) mechanism.
This is a solenoid that usually lives somewhere near the bottom of the
shift lever. You may be able to hear it "thunk" if you put your ear by
the shift lever while pushing on the brake pedal.
The wiring diagram above shows that there is a shift lock ECU that has
a wire from the brake light switch, as well as direct wires from two
other fuses. I think the brake light signal is probably an input to
the shift lock ECU, rather than a power source for it, but a short on
the brake light signal wire would still blow the brake light fuse. If
the car has a console shift, sometimes coins, soda, etc falls in around
the shift lever; usually it just makes a mess but something metal might
eventually wear through a wire.
I hope this helps!
Matt Roberds
