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-   -   Chasing a short... (http://www.risingsun4x4club.org/forum2/showthread.php?t=20867)

Rezarf 02-10-2014 01:17 PM

Chasing a short...
 
A my 1995 Corolla is blowing brake light fuses. It started last fall and I'd get a few weeks between popping a fuse. Now it pops at the first touch of the brakes. I know the basics on chasing a short but I've never had to work too hard for the solution. Currently I know my brake switch is not faulty, I have to use the shifter override soleniod thingy by the shifter to get it out of park. My bulbs work when I first depress the brakes.

I'm thinking my order of tracking this down is as follows, please comment if you'd do it differently and why...

Probably swap out the bulbs just to make sure I am starting with fresh working bulbs.
I've already replaced the brake light switch under the dash to confirm that was not the primary issue.
I'm basically looking for continuity for power right?

How would you start? Brake lights to the switch or switch to the brake lights?

I've got a few things that need attention in the dash consol, like the lights and cig lighter, I might take a look there first since I know there are issues.

Thoughts?

DaveInDenver 02-10-2014 01:35 PM

You say the brake lights come on before the fuse blows? My first step would be to verify the bulb sockets and housings are not corroded or have broken wires. Fuses blow because of high current and unless you've changed something (like adding a trailer harness is one common change) you have to track down why the current is higher than Toyota intended. Rust and corrosion on wires, connections and contacts is 99.999% of the time the reason.

Rust has a much, much higher resistance than clean copper or steel. If I had to guess years of mag chloride and moisture have changed the copper in the connections into nasty, green messes. Pull off the connectors throughout the circuit and see, could be in the housing or anywhere between the pedal or anywhere. A service manual would be handy, it's possible the harness is not all that simple as a point-to-point and probably gets bundled into a couple of big connectors under the dash.

In Cruisers this happens because the housing itself is rusting in the rear frame member and that might be the problem here, but it's less likely because harnesses now contain the circuit return since stuff is made from plastic and doesn't ground through the housing itself.

SteveH 02-10-2014 02:29 PM

I would look hardest at the harness at the rear of the car, especially (as noted) if trailer lights were added, or if there was collision repair (and pinched wires).

You might also remove all the bulbs, put a brick on the brake pedal to energize the circuit, and then re-install the bulbs one-by-one until the fuse blows. This might tell you if it's one particular socket/wire, or the entire circuit.

If you can get a schematic, you might see if there are any other modules or doodads attached to the brake light circuit - such as a brake light minder or a cruiser control kickout. A Corolla is less likely to have this stuff, but you never know.

bomber22 02-10-2014 05:33 PM

steve's 2nd idea sounds pretty good to me, i use my snow brush to hold the pedal down. but, unless you are going to pull your offroad camper with the corrolla, i dought that you installed trailer lights.:lmao:

simps80 02-10-2014 08:42 PM

I had a 89 or 90 camry with a bright yellow brake light control box in the back that was bad. It would make the brake light switch go out under the pedal then same problem with the shifter..
I forget what it was called but it was bright yellow and the size of a pack of cigarettes..repeated havoc till I found that in the circuit and swapped it

Squishy! 02-10-2014 11:41 PM

Also check the harness where it bends at the trunk lid.

AxleIke 02-11-2014 07:42 AM

Quote:

Originally Posted by Squishy! (Post 246224)
Also check the harness where it bends at the trunk lid.

This ^

I've had two shorts in the bendy parts of harnesses and they were inside the loom. The wire insulation had gotten brittle from age, and the constant movement caused them to crack and short, except it was impossible to see since it was all wrapped up.

I would start at the back of the car and work forward. But where things are exposed or move, pull back the loom/tape and inspect.

Rezarf 02-11-2014 09:50 AM

Thanks everyone, this has given me some good steps to try, I appreciate it. I have a schematic and I'll start at the rear and move forward. Thanks again, if you guys think of anything else I am all ears.

SteveH 02-11-2014 10:34 AM

I had a 89 or 90 camry with a bright yellow brake light control box in the back that was bad. It would make the brake light switch go out under the pedal then same problem with the shifter..
I forget what it was called but it was bright yellow and the size of a pack of cigarettes..repeated havoc till I found that in the circuit and swapped it


I had this happen in the same gen Camry - a cold solder joint in the board of the 'brake light computer', high up inside the trunk on the left side. Once soldered, it worked fine again.

Squishy! 02-12-2014 09:38 AM

Quote:

Originally Posted by SteveH (Post 246230)
I had a 89 or 90 camry with a bright yellow brake light control box in the back that was bad. It would make the brake light switch go out under the pedal then same problem with the shifter..

I forget what it was called but it was bright yellow and the size of a pack of cigarettes..repeated havoc till I found that in the circuit and swapped it




I had this happen in the same gen Camry - a cold solder joint in the board of the 'brake light computer', high up inside the trunk on the left side. Once soldered, it worked fine again.


I don't believe the Corolla has this. The Camrys had a "brake light out" indicator and the corollas did not. I could be wrong though.


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