I spent about 8 hours so far today trying to figure out why I have no brake lights or hazards. The brake lights and hazards would not work last week. I had power to the orange wire on the brake light switch and put in a new hazard flasher with no luck so I figured the issue was in the turn signal switch so I ordered a new one. Now I am in the same boat even with the new switch installed: no brake lights and no hazards. I have tested the circuits and this is what I come up with:

With turn signal switch (harmonica connector) disconnected, and testing the female part of the harness I am getting:

+ voltage with a test light at both the black wire and brown wire

+ voltage with a test light at the white wire when I press down on the brake (so the brake light switch works, and I just replaced it today anyway).

Continuity with ground at the Lt blue, dk blue, green, and yellow wires (makes sense as they go to ground through the bulbs)


With either the new or old turn signal switch connected I get:

Continuity with ground at the same four wires above plus the white wire


If I push the hazard switch on, only the black wire has + voltage, not the brown one.


If I press the brake pedal, the brown wire goes dim on the test light. Even after the brake is released, all wires except the light green and tan ones have continuity with ground.


Please help! I am probably missing something stupid here, but my patience is wearing thin!

 

Did you check the grounds to both tail lamps?

 

your brake lites get their power , from the hazard flasher right at the hazard flasher connection, should be large org. and a small org. wire. the small goes to the brake light switch, the big one gets power from the fuse box.
you probable have a bad connecion inside the fuse box.
trace back the supply voltage.

 

Thanks for the quick replies. i will check the tail lamp grounds and the orange wires for the hazards and stop light switch.

 

Ok, where and how do i check tail light grounds? i pulled fuse panel back, but i can't see the orange wires behind it

 

The gnd is at the light housing themselves. At least they are on my '71. Most time corrosion and old age causes the grounds to go bad.

 

Hi h...,
Here's the typical ground connection (71) on the rear lights, it's the black wire, and it loops from light to light for each pair.
Good Luck!
Regards,
Alan

 

Ok i just found that the lower left terminal for hazard flasher is grounded. i don't think it should be so maybe there is a short?

 

Reattach the harmonica connector,press on the brake and using your 12v test light test both sides of the white wire at the harmonica connector,if both sides are hot then test the yellow and dk green on both sides of the connector.

On your hazard flasher grounding-one term is power and the other is connected to the bulbs-as you stated above its normal to show continuity to ground through the bulbs.

 

I had this same problem awhile back on my '73. I checked everything multiple times and could not find the problem initially. I kept checking the fuse with a test light and it showed to be fine. A look at the wiring diagram revealed that the right terminal of the stop/hazard fuse (orange wire) went directly to the hazard flasher (mounted on the upper left of the fuse block). From there, another orange wire continues on to the stop lights.

I finally determine my problem had to be with that short orange wire and I pulled the fuse block expecting to find that wire disconnected at either the fuse or flasher end. Turns out it was connected solid with no problems. Scratched my head a bit and then pulled the fuse again. This time I noticed the fuse holder had a little corrosion. I cleaned both terminals of the fuse holder very well, applied some dielectric grease, put the fuse back in, and bingo I had the circuit working again.

Hope this helps.

DC

 

That's the "fuse looks fine" fooler, the test light is our friend,always test the fuse end and the fuse holder. Thanks for sharing.

 

Yep, I learned that lesson but only after hours chasing electric gremlins. First time in all my years of tinkering with cars I've had a fuse holder issue. The bad thing was that I had removed all of the fuses a couple of years before that, cleaned all the fuse holders and reinstalled with dielectric grease. After examining this particular fuse holder more carefully this time, I realized I had not cleaned it well the first time.

DC

 

Thanks for all the replies. I tried everything and eventually found that there is a short between the white and orange wires somewhere that supply the brake light switch and hazard flasher to harmonica connector. Rather than wasting more time, I ran a new fused circuit from the "BAT" part of the fuse panel to the flasher and to the brake light switch, then to the brown and white terminals on the harmonica. Everything works fine now. For good measure I cleaned the lighting grounds as well.