Blown Brake Light Fuse

[ZNate]

After fixing the short causing the fuse link to blow in my 9/70 240Z, I now have brake light issues.  I have searched the forums, but have not found this exact issue discussed or anything that I can apply.  

If someone could help me narrow down the search I would appreciate the assistance.  I’m assuming it is a switch issue, but do not want to take them apart again unless it is required.

The brake lights work (three bulbs each side) when the brake is depressed.  However, if the turn signal or the hazard lights are used, the brake light fuse blows.

Turn signal lights, hazards, headlights and driving lights operate correctly before/after the brake light fuse blows.

Items of note:
1. Taillights were removed/refurbished over the winter and reinstalled this spring.
2. Recent issue with defrost switch/Acc Relay circuit short identified and successfully repaired.
3. Fuse box, hazard switch, turn signal and combo switch cleaned two years/2000 miles ago.  No issues until now.
4. Brake switch is new.
5. Brake circuit is powered directly from the battery to the brake switch with a 15 amp ATC fuse (which currently blows).  No fuse issues in two years until now.  I cannot remember who I purchased this bypass kit from at this time.

Thank you!
Nate

[Zed Head]

The wiring diagram shows both circuits passing through the Hazard switch.  T/S and Stop seem to be on the same wire.  I think the 240Z circuits are different than 1976.  Not really sure how the various bulbs and filaments are controlled.  Looks complicated.  Is three bulbs (six bulbs) for brakes normal?  The diagram shows Tail as independent.  Might just be too many filaments on one fuse.

 

 

[SteveJ]

I did this drawing several years ago to address some of the confusion on the turn signal/hazard light/brake light circuit. While it is specific for the 72, the 70 should be pretty close. Some of the connectors may be different.

https://fiddlingwithzcars.wordpress.com/2013/01/20/hazard-switch-brake-light-turn-signal-circuit-analysis/

[ZNate]

Thank you Zed Head and SteveJ for the advice and easy to read schematic.  it's much better than the magnified hard copy I have.

I was doing a test with the brake light bulbs removed, brake pedal down, headlights on and then used the turn signal.  I saw and heard a quick flash inside the turn signal housing.  In addition, the wire and temporary fuse from the battery to brake switch got warm.

Not sure if that identified a short in the turn signal switch or the extra amps from a short somewhere else.  What do you think?  I'm leaning towards removing and checking out the switch.

Thank you!

Nate

[ZNate]

Saw a loose wire, so I repeated my test.  No more flashing sparks, but my left side blinkers stopped working.  Going to take the turn signal switch apart to investigate and repair.

[Zed Head]

Take a look at the Stop switch wires.  Your brake lamp jumper wire is a sign that somebody was trying to fix a problem.  Might be better off to go back to original and see if you end up with the original problem, which might be easier to solve.  You're working around somebody's hack now.

[ZNate]

Thank you Zed Head for the suggestion.  That will be my next step if the turn signal repairs do not fully resolve the problem.

Upon disassembly of the turn signal switch I discovered the bearing out of place, which melted part of the bearing housing containing the spring.  I cleaned the switch, reassemble it and installed it again.  Brake lights and turn signals worked on one side, but not the other.  The switch also did not operate correctly.

Tomorrow I will take my time fixing it and utilizing parts from a spare switch.  Will provide an update tomorrow.

[ZNate]

All fixed!  The issue causing my brake light fuse to blow was a faulty turn signal switch.

As stated above, I got the turn signal switch to partially work yesterday, so today I disassembled it again for repairs, but it failed testing with an ohm meter.  I think too much plastic melted into the contacts and I was unable clean it good enough.  See attached photos.

Luckily I had a spare switch from a later model 240Z (longer wiring harness) that was a perfect match.  I was easily able to coil/roll-up the longer harness under the steering wheel.

Glad to be back on the road to enjoy a Wisconsin summer.

Nate (ZNate)