Brake & Hazard Light Mystery

[DC3]

Took the '73 out of town this weekend. When I arrived at my destination, I had no brake lights or hazard lights. Both were working fine the day before. Everything else worked fine. Fuses were good. Bulbs were good. Tail lamps were good. Turn signals were good. Backup lights were good. Headlights were good. Both flasher modules were good. Everything else was good. The ground connections looked good and since the turn signals worked, I didn't figure to have a grounding problem.

I pulled the wire off the brake light switch and jumpered the terminals but no luck. Apparently the brake switch is good. A buddy said the power feeds through the turn signal switch. We found a reference on the web that said if you have 12 volts to the white wire at the harmonica connector at the base of the steering column but no brake or hazard lights, that the problem was in the turn signal switch. Only problem is I didn't have 12 volts on the white wire.

I pulled the wire back off of the brake light switch and checked for voltage at both terminals but had no voltage. So apparently I had a loose connection somewhere. Had is the operative word as I took a buddy for a ride after failing to fix the problem and, while driving around, the brake and hazard lights started working again.

So, I've got an intermittent open circuit somewhere. The question is where? Is there a connector hidden somewhere I should check? The orange and white wires from the brake switch go into the harness that loops over the top of the speedometer. I really don't want to have to pull the dash for this. Any ideas?

Thanks

DC

 

[Twin_Turbo]

Check the harmonica connector, I've had the connections pull out of it.

 

[mrvette]

Check the harmonica connector, I've had the connections pull out of it.

I hate it when my harmonica looses toon.....

I would be looking at a bad ground in the rear.....on my '72 it was the left/drivers rear frame near the muffler....

this SHOULD be easy to find with a voltmeter....I would hope...

:flash:

I reread you post above, you DO have a grounding problem.....

because the dual filament bulbs of the 1157 have that shell supposed to be connected to ground...but ONE side of the bulb is connected to headlight circuit....comes on/off from same power source.....fine....the other end of the headlight bulb is grounded......think for a second, the power hits the rear bulbs, and feeds back through the heavy load of the headlight circuit.....to ground....so the lights don't light at full power, BUT they do light.....

but the other section of the bulb will NEVER light....

 

[DC3]

Check the harmonica connector, I've had the connections pull out of it.

I didn't see any issues with the harmonica connector. I wasn't getting voltage to the wire going to the harmonica connector. Doesn't that mean the problem is between the fuse and the harmonica connector?

DC

 

[DC3]

I reread you post above, you DO have a grounding problem.....

because the dual filament bulbs of the 1157 have that shell supposed to be connected to ground...but ONE side of the bulb is connected to headlight circuit....comes on/off from same power source.....fine....the other end of the headlight bulb is grounded......think for a second, the power hits the rear bulbs, and feeds back through the heavy load of the headlight circuit.....to ground....so the lights don't light at full power, BUT they do light.....

but the other section of the bulb will NEVER light....

Not following you. Isn't the bulb socket the ground for both the tail light filament and the brake light filament? The bulb has two contact points on the bottom, one for tail lights one for brake. Tail lights work fine so ground is good.

DC

 

[mrvette]

I reread you post above, you DO have a grounding problem.....

because the dual filament bulbs of the 1157 have that shell supposed to be connected to ground...but ONE side of the bulb is connected to headlight circuit....comes on/off from same power source.....fine....the other end of the headlight bulb is grounded......think for a second, the power hits the rear bulbs, and feeds back through the heavy load of the headlight circuit.....to ground....so the lights don't light at full power, BUT they do light.....

but the other section of the bulb will NEVER light....

Not following you. Isn't the bulb socket the ground for both the tail light filament and the brake light filament? The bulb has two contact points on the bottom, one for tail lights one for brake. Tail lights work fine so ground is good.

DC

1157 bulbs have two filaments, one is brighter than the other, draws more current, I forget which job is for which filament....but at any rate, IF the ground is no good the bulb base 'floats'....because the supposed ground side now finds ground through the other thicker filaments, and the main lighting circuit they attached to...call it a resistor in series if you have to...the silly sucker will be dimmer, but if you took a lens off and looked that the bulb you maybe see the 'other' filament lighting really dim when you think it's working normal....

sorry I don't know how else to explain it....but 'ground' is being found through another path from the bulb internal structure....

:flash:

 

[DC3]

1157 bulbs have two filaments, one is brighter than the other, draws more current, I forget which job is for which filament....but at any rate, IF the ground is no good the bulb base 'floats'....because the supposed ground side now finds ground through the other thicker filaments, and the main lighting circuit they attached to...call it a resistor in series if you have to...the silly sucker will be dimmer, but if you took a lens off and looked that the bulb you maybe see the 'other' filament lighting really dim when you think it's working normal....

sorry I don't know how else to explain it....but 'ground' is being found through another path from the bulb internal structure....

Ok I get it but that is not my problem. Turn signals worked properly at normal brightness with no dimming issues and with no voltage to the brake switch, there has to be an open circuit issue. Just for grins I checked the grounds at the back of the car and they all were good. I'm pulling the fuse block this weekend to look for a poor connection in the orange wire somewhere between the fuse and the brake switch.

DC

 

[mrvette]

Seems kind of stupid to ME, but the orange wire to the brake light sw should be always hot....ign on or off....so if the pedal is pressed the rear lights will light when 12 goes to the white wire, energizing that section of the bulbs....

I don't understand why it's NOT a switched hot, but it snot....

so put your meter on the orange wire, if not hot all the time, you gotta fuse/block problem....if you do, press the pedal, that 12 disappears you gotta bad connection, first off is the fuse itself, and the steel clips in the fuse block....then to the wiring....

I have seen these fuse blocks get RUSTY in their construction as the fuse clip/springs themselves are steel...for the fuse retention....lousy system IMO....not a fan of glass 1/4 inch fuses....I seen them 'blow' from bad...HOT contacts on the clips that will melt the internal soldered connection to the fuse link itself....seriously....the fuse LOOKS good, but it snot....

IF you pull it apart, you well maybe find some seriously bad corrosion and it snot the first one in my experiences....especially in old leaky vettes...:flash:

 

[DC3]

IF you pull it apart, you well maybe find some seriously bad corrosion and it snot the first one in my experiences....especially in old leaky vettes...

I had pulled all the fuses last year and cleaned the contact clips and used dielectric grease when I put it all back together. The fuse was good so it is looking like my problem is behind the fuse block. I'll pull it this weekend and have a look.

DC