Topic: Dash lights coming on when pressing brake pedal

[Chris]

My 15 amp fuse has been frequently blowing lately and I was unsure why. Now I'm seeing my dash lights come on everytime I press in the brake pedal. It looks like a short somewhere. Has anyone seen this before?

Chris

[midlife]

What year?  This sounds more like a grounding problem (for dash lamps lighting).  Which 15 amp fuse is blowing?  Describe its position in the fuse box.

[Chris]

This is my June 64 1/2 convertible, 260. The 15 amp fuse blowing is in the lower right fuse slot in the 64 1/2 style fuse holder, owner booklet shows this as 15A AUX.

[midlife]

That's the fuse power line for the brake pedal switch, which routes through the headlight switch, IIRC.  You might have a bad headlight switch, or a pinched wire somewhere.  Try removing the lines from the brake master cylinder/switch in the engine compartment and see if that keeps the fuse from blowing.

[Chris]

I checked for loose wires and did not find any, car was blowing the 15 amp fuse about every 4 minutes of run time (and when the headlight switch is on). I removed the wires from the brake master cylinder switch under the hood, drove the car for about 30 min and the fuse did not blow, brake lights and dash lights stayed on.

Not sure what this means though.

[midlife]

I checked for loose wires and did not find any, car was blowing the 15 amp fuse about every 4 minutes of run time (and when the headlight switch is on). I removed the wires from the brake master cylinder switch under the hood, drove the car for about 30 min and the fuse did not blow, brake lights and dash lights stayed on.

Not sure what this means though.

I don't either.  If you disconnected the wires at the master cylinder, then the brake switch is now disabled, and you should have no brake lights.  When you drove the car, was the headlight switch on?  If so, that would at least explain the dash lamps.  If headlight switch is off, there's something very screwy going on, and the headlight switch would be my focal point, as that is the source of both brake light power and dash lamps.  The brake lights, though, have to go through the brake switch to be powered up.  I wonder if by disconnecting the switch from the master cylinder, it defaults to making the connection.  I've never seen a 64.5 brake switch. 

Disconnect the headlight switch plug and see what you get.  If OK, reconnect the master cylinder switch and see what you get.  Process of elimination....

[Chris]

Yes, I had the headlights on. With the break light switch disconnected, the headlights, dash lights, and tail lights all work but I have no break lights. I don't know why having the break lights disconnected keeps the fuse from blowing...is it because adding it is just too much amps for the headlight switch?

I can try the other steps you mentioned tomorrow.

[Chris]

Just to clarify, with the break light switch disvonnected, all else operated fine (headlights, tail lights, dash lights) and the 15 amp fuse did not blow. The test was done with the headlights turned on. This is how I could see if the dash lights were staying on and the fuse remaining ok. When everything is connected (to include break light switch) and the headlight switch is on, after a short time the 15 amp fuse blows taking out the dash lights, tail lights, and break lights. Only the headlights remain on. This only happens at night when I'm running the car with the headlights on. 

[midlife]

Aha!  I suspect the problem is a pinched wire or a shorted something or another at the rear tail lights.  So try this: connect everything up, and disconnect the two rear light sockets.  Does that allow everything to work (obviously not the brake lights or running lights at the rear) without blowing the fuse?  If so, then connect the sockets and remove the bulbs.  Does that work without blowing the fuse? 

If so, examine the rear tail wiring very carefully; I'll bet something is amiss back there.  Check carefully the grounds.

So why do the dash lights come on when the brakes are pressed?  The lights are seeking a ground path, and the path they find are the dash lamp circuitry through the headlight switch. 

[Chris]

I reconnected the break (BRAKE)lights at the master cylinder under the hood and disconnected the bullet connecters in the trunk where they connect to the pig tails for the tail lights. I then drove around for 5min or so and the 15amp fuse did not blow. I then reconnected the bullet connectors at the tail lights but removed the light bulbs. I drove around for another 5min and the fuse did not blow. I'm about to put the bulbs back in and leave everything connected, drive for 5min and see what happens...want to see if fuse blows, need to make sure I was driving long enough.

[67gtasanjose]

]

My 15 amp fuse has been frequently blowing lately and I was unsure why. Now I'm seeing my dash lights come on everytime I press in the brake pedal. It looks like a short somewhere. Has anyone seen this before?

Chris

Aha!  I suspect the problem is a pinched wire or a shorted something or another at the rear tail lights.  So try this: connect everything up, and disconnect the two rear light sockets.  Does that allow everything to work (obviously not the brake lights or running lights at the rear) without blowing the fuse?  If so, then connect the sockets and remove the bulbs.  Does that work without blowing the fuse? 

If so, examine the rear tail wiring very carefully; I'll bet something is amiss back there.  Check carefully the grounds.

So why do the dash lights come on when the brakes are pressed?  The lights are seeking a ground path, and the path they find are the dash lamp circuitry through the headlight switch. 

Make 100% sense! A "No Ground" situation would indeed backfeed through the bulb and overload the stop light fuse while trying to carry the extra load of the tailight/dash lights.

I reconnected the break (BRAKE)lights at the master cylinder under the hood and disconnected the bullet connecters in the trunk where they connect to the pig tails for the tail lights. I then drove around for 5min or so and the 15amp fuse did not blow. I then reconnected the bullet connectors at the tail lights but removed the light bulbs. I drove around for another 5min and the fuse did not blow. I'm about to put the bulbs back in and leave everything connected, drive for 5min and see what happens...want to see if fuse blows, need to make sure I was driving long enough.

You MAY have inadvertently caused the brake lamps to get a decent ground so if everything works right now, I would look at the bulb sockets for rust or corrosion. 

[Chris]

Here are pics of the lights sockets, think there is some corrosion on one of them.

[Chris]

The lights no longer come on in the dash when pressing the break pedal. That stopped yesterday after I opened up the dash lights and checked all the connections.

[67gtasanjose]

Here are pics of the lights sockets, think there is some corrosion on one of them.

Those look like pewp! I would be restoring/replacing the whole lamp & pigtails. The disk in the one that I can see is warped, pushing the contacts towards one another...bad news!

[Chris]

Yes, here is a better look at the driver side contacts, some weird insert with a spring. The seperator for the contacts is letting them touch, or almost touch...would this cause a short?