hey everyone.   I am working on an 83 ea81 wagon.   The car is blowing the brake fuse (10 amp) consistently.  

  Ok... the brake circuit is hot all the time ... even with ignition off... this is normal and per design... correct?    So the vehicle is sitting in the driveway ... fuse in place ... nobody within 20 feet.    Wait for it ... what's that smell ... smells like burnt electrical components.

  I check the fuse ... and it is blown (again and again).

  Here is what I think I know and have checked.   I pulled the fuse box and checked the back side for shorts .  I blew it out with compressed air.  Everything is clean.  

  There are 2 wires for the circuit.  A big hot wire (white with black stripe) and a smaller wire looks like light green, which I think goes to the brake pedal switch.  When the brake pedal is pressed, it should complete the circuit to the brake lights.   The brake lights  do work when I press the pedal.   When I release the brake pedal, the brake lights go out... all good, right?

  However, let the car sit there for 20 minutes, and it will blow the fuse.  I can actually smell something burnt. 

  So there must be some draw on that circuit between the fuse box and the brake pedal switch?  Maybe... I don't know.

  When the fuse is pulled, checking with the multimeter,  I put one lead on the power in and one lead on the power out contact, and I do read some ohms.  I'm not exactly sure what this means.   But the same check on other circuits (fuse pulled) show no continuity.

  Any help would be appreciated.   Sorry about the long post.   Please help.   Ron w.

if you disconnect the plug at the switch does it still pop?

hey everyone.   I am working on an 83 ea81 wagon.   The car is blowing the brake fuse (10 amp) consistently.  

  Ok... the brake circuit is hot all the time ... even with ignition off... this is normal and per design... correct?    So the vehicle is sitting in the driveway ... fuse in place ... nobody within 20 feet.    Wait for it ... what's that smell ... smells like burnt electrical components.

  I check the fuse ... and it is blown (again and again).

  Here is what I think I know and have checked.   I pulled the fuse box and checked the back side for shorts .  I blew it out with compressed air.  Everything is clean.  

  There are 2 wires for the circuit.  A big hot wire (white with black stripe) and a smaller wire looks like light green, which I think goes to the brake pedal switch.  When the brake pedal is pressed, it should complete the circuit to the brake lights.   The brake lights  do work when I press the pedal.   When I release the brake pedal, the brake lights go out... all good, right?

  However, let the car sit there for 20 minutes, and it will blow the fuse.  I can actually smell something burnt. 

  So there must be some draw on that circuit between the fuse box and the brake pedal switch?  Maybe... I don't know.

  When the fuse is pulled, checking with the multimeter,  I put one lead on the power in and one lead on the power out contact, and I do read some ohms.  I'm not exactly sure what this means.   But the same check on other circuits (fuse pulled) show no continuity.

  Any help would be appreciated.   Sorry about the long post.   Please help.   Ron w.

 

Not that it will help much, but you should check from the "power out" side of the fuse holder (fuse removed) to ground.  With the pedal up that should have no continuity.  If it has continuity, either the brake pedal switch is bad or there is a short between that side of the fuse holder and the brake pedal.  The quick and easy solution will probably be to run a new wire from the fuse holder to the brake light switch.  Good luck, sounds like it will be a fiasco.

I'll try both the above tests and report back.  Thank you for the tips.

Ok, here is what I find.     I disconnected the plug at the brake pedal switch.   There are two green wires in the plug.  I am thinking one green wire is coming from the fuse box ... and the other green wire goes to the brake lights.    I have 100% continuity on one green wire - so I assume this is the wire that goes to the brake lights, thru the bulb and then to ground - so zero ohms, zero resistance.   Is this correct?

  The other green wire is coming from the fuse box.  When I test that lead (at the plug that is disconnect to the pedal switch), I get an partial ohm reading.  So that wire is 'somewhat' grounded between the fuse box and the plug end.

  My thought is just replace that wire from the fusebox to plug.   Can I just pull the wire from the back of the fusebox with a needlenose?

Ok, here is what I find.     I disconnected the plug at the brake pedal switch.   There are two green wires in the plug.  I am thinking one green wire is coming from the fuse box ... and the other green wire goes to the brake lights.    I have 100% continuity on one green wire - so I assume this is the wire that goes to the brake lights, thru the bulb and then to ground - so zero ohms, zero resistance.   Is this correct?

  The other green wire is coming from the fuse box.  When I test that lead (at the plug that is disconnect to the pedal switch), I get an partial ohm reading.  So that wire is 'somewhat' grounded between the fuse box and the plug end.

  My thought is just replace that wire from the fusebox to plug.   Can I just pull the wire from the back of the fusebox with a needlenose?

 

hahhahaha you can probably just pull that wire from the back of the fusebox with a pliers, but I wouldn't recommend it!  There might be a tab of some kind holding the wire in, if you can figure that out and pull the wire out easily, great.  Otherwise you will probably have to cut and splice.

 

Do you have a voltmeter?

The wire that has continuity to ground probably goes to the brake lights.  If the car just has the two bulbs for the brake lights, you could remove them and see if there is still continuity.  More of a hassle if you have a half dozen bulbs for the CHMSL (center brake light).

The other wire should have 12VDC compared to ground.  You could remove the fuse and make sure it has 0V.  Most likely this wire is grounding somewhere between the switch and the fuse, I assume it's what you're going to replace.  If you can follow it, I'd see if I could find a spot where the insulation is worn through since there are probably other wires that have or will have the same issue.

Might as well double check that the switch is working with your continuity tester while you're there.

Just got off work... it's 7:25 p.m.   so I think I'll have a beer, first.  I wish pontoontodd was here to enjoy a frosty one.

  Yes I have a voltmeter.  No center brake light.  '83 just has the old school brake lights.

  I will pull the brake bulbs and make sure I then have 0 continuity to ground.

What I did notice, is that the 2 green wires that come out of the HUGE wiring harness have black tape wrapped around them inclusively.   I thought this is strange.   Has anyone seen this same black wrap around those two green wires that go to the brake pedal switch?

  I fear that if I add new hot wire from fuse box to brake switch, then the return wire (from pedal) to brake bulbs may have a ground issue.

  So the question is do those two green wires have stock black wrap ... or did previous owner wrap them? 

  Hard to follow wires up under the dash when they are in wrapped harness.

  Anyone, like GLoyale, can tell me if I can pull plug from back of fuse box with needle nose?   If not pull easy, then I can cut and splice.  But I don't like soldering upside down ... ahhhhh... burnt facial skin ... not good!

If the switch is working properly, it's open when the car is sitting there, so even if you had an intermittent short to ground after the switch it wouldn't blow the fuse when the car is parked.

You can always use crimp splices, pull real hard when you're done to make sure it's a good connection.

So, if you disconnect the plug at the brake switch and leave the car sit, doe it still pop the fuse?

If so, then the problem is somewhere between the fusebox & the brake switch, not the switch or anything further down.

 

I haven't worked on an 83, but did some fuse box changed on an 85, and can confirm that you can pull the pins out, but they're a right bugger, and almost impossible whilst it's still in the car. It's also prob a 2 person job. I discovered how by going to the wreckers and literally smashing apart a fusebox to look how the pins clipped in.

 literally smashing apart a fusebox to look how the pins clipped in.

that's hysterical

I have to go to my Jay Oh Bee.    I'll check to see if the fuse blows with the switch unplugged.     I want to be there watching it ... so my car don't burn.   With my testing, it seems that the green power wire to switch is grounding.    If all confirms tonight, I will run a new wire to switch.

  Have a great day everyone... and thank you all for your help.    ron w

Look for a place where the wiring has been bumbled with by someone, such as stereo wiring. Or possibly damage from an accident. 

 

Soobs RAREly ever develop electrical problems like this on their own.

 

I always go right to where it has been fooled with, and 99 percent of the time, there it is.

Replace the fuse with a brake light bulb for testing purposes. If / when it is lit, and how brightly, will show when you have a circuit vs short Circuit, etc.

DaveT ... pray tell, how do I put a 1057 bulb in the fuse box.   Is the outside of the bulb the positive?

   I'm still at work.   I'll see if it fits when I get home.

DaveT ... pray tell, how do I put a 1057 bulb in the fuse box.   Is the outside of the bulb the positive?

   I'm still at work.   I'll see if it fits when I get home.

 

There are some small bulbs with leads on them that you might be able to plug in, I think some of them are size 97.

 

The outside of a 1057 is the ground, but it doesn't matter for an incandescent bulb.  If you had a bulb holder with the wires you could strip the ends of the wires and shove them in place of the fuse.

 

I like the idea of unplugging the brake pedal switch and seeing if the fuse still blows, that would help narrow down the problem.

No, just find wires or test leads or something.  MAybe a blown fuse, solder wires to it, so it will still clip in.  This is a testing thing, not for driving with, etc.

The point of using a moderate size bulb is to allow enough current to flow to help locate the problem.  It will light up instead of blowing, saves $ on fuses.

A plain ol automotive test light is a great tool for this job, and my tool of choice for most electrical diagnosis.

 

Harbor freight has them for a few bucks. 

 

Add one or two alligator clip jumper leads and a couple of large paper clips with one end straightened out for inserting in connectors (such as fuse holders), and you have all you need for most any diagnosis. 

Test Results.   Ok... with the brake switch unplugged (at white connecter), the fuse does not blow.   I actually put in a 5 amp fuse, rather than the 10 amp fuse... thinking it would blow quicker and not let the wires heat up.    So, the problem seems to be either the brake switch or downstream to the brake lights.

   However, the brake switch seems to work ok.  With pedal pressed, the brake lights come on.  With pedal in normal resting position, the brake lights are off.

   So now, I test the green/yellow wire that goes to the brake lights (after it leaves the switch).    I have 100% continuity with the bulbs in - this is correct.   With the brake bulbs out, I have zero continuity to ground - good news - no grounded wire between switch and brake bulbs.

   So, it has to be the switch... right?     Maybe the switching mechanism works ok .... but also has a faulty ground in the metal body of switch.   How should I test this theory?

I would start with replacing the brake switch.

Is it possible when you plug the connector in it's pulling on the wire and grounding/rubbing somewhere?

 

So, it has to be the switch... right?     Maybe the switching mechanism works ok .... but also has a faulty ground in the metal body of switch.   How should I test this theory?

 

Put your ohmmeter between the switch body and input after unplugging.

Operate the switch.

Condemn it for anything other than infinite ohms.

 

While you are at it,check resistance to ground of the output wire to the lights.

Should be no less than 1/2 the resistance of a brake light bulb element.

Might want to shake the harness etc. while testing.

 

I use a circuit breaker in place of the fuse for these situations.

Saves a lot of fuses.

UPDATE...    I ohmed the switch body to input.  No continuity (infinite ohms)... All good.

   Ohmed the output to lights ...   No ground issues there.

  Scratched head - ALOT.    Plugged the brake switch in, put in 10 amp fuse ...  brake lights work ... 2 days and fuse is still good.    So, I think I fixed it ... for now.   However, all I did was pull fuse box and blow out... pull wiring harness down ... inspect ... unplug and plug switch.    There must be a hidden ground issue ... somewhere.

  Can anyone tell me if there are any other accessories (or lights) on the brake circuit?       Could it be the reverse lights ... what circuit are those on?

FSM list of things on that circuit

 

Stop light

Trunk room light

Door pilot

clock

 

Any chance the trunk light wires or switch have a short?  pinched in the hinges?

thank you for the info, GLoyale.    I'll check the trunk light switch.  The hatch was OPEN all day when I was working on the issue.   I did see the clock listed on the fuse box lid ... however, when I pull the fuse, the clock is still on. 

  Can you tell me what the door pilot is?

thank you for the info, GLoyale.    I'll check the trunk light switch.  The hatch was OPEN all day when I was working on the issue.   I did see the clock listed on the fuse box lid ... however, when I pull the fuse, the clock is still on. 

  Can you tell me what the door pilot is?

 

Dash display that shows which doors open.

 

Probably just the clock memory on that circuit, and the display of the clock is on Ig. switched circuit.