no brake lights

carol ann

carol ann

Member
i have a late 1931 model A that runs great. Haven't done anything electrical to it since I got it and I was hoping this scenario would ring a bell for the many experts out there. When I turn on the cowl lights or headlights, both tail lights and stop lights work. However when I press the brake pedal alone neither brake light works and the amp meter doesn't move. I would appreciate any recommendations on how to start troubleshooting. Many thanks
 
That does sound a bit tricky. You say the brake lights work properly if the tail lights and tail lights are on, but do not work at all if headlights and tail lights are not turned on. Sounds like the power going to your brake light switch might be coming from your headlight switch and not off the battery. It should be wired so that as soon as the key is in a run position you have power to the brake light. You might want to try to follow your wire form the brake light switch back to its source. Maybe at one time the ignition switch was replaced and not wired back correctly. I am no expert when it comes to electrical, but this is what it seems to me.
 
For some unknown reason Henry routed the power to the stop light switch through the light bale, where there can be electrical faults due to the nature of the construction, especially if it is a reproduction. If you are out on the road and a short circuit occurs in the light bale and blows the fuse you can disconnect the wire that runs from the generator to the light bale, and continue on your way during daylight hours. However, you will not have stop lights. A very easy and prudent modification to incorporate is to disconnect the wire at the stop light switch that comes from the light bale, fold it back and wrap black take around it. Run a new wire from where the old wire was removed to the fuse or to one of the terminal lugs on the firewall. this makes the stop light switch independent from the light bale and very easy to trouble shoot. It also allows you to continue on with power disconnected to the light bale during daylight hours and still have stop lights.

Tom Endy
 
How about the bulbs (6Volt)? may have shorted out and blown! oh I see it says work may be the wire to the brake switch or the switch itself.
 
Humperhill said:
It should be wired so that as soon as the key is in a run position you have power to the brake light.
Click to expand...

This is incorrect. There should be power to the brake light switch regardless of the key position. The brake light circuit is not even wired to the ignition switch. the brake lights get their power thru the light switch at the bottom of the steering column.
 
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Just a thought. While you're checking other things ensure your tail lights have a good ground. You could possibly be back feeding the brake lights. That would explain why the brake lights work only when the running lights are on. Bad grounds cause strange thing to occur in an electrical system.
 
thank you all for sharing your thought process with me. once i figure out what is going on i will let you know.
 
Thanks for the link, carol ann, I hadn't seen such a complete and comprehensive article before.

As for your problem, my guess is that the brake switch (green wire) is connected to the same lighting switch terminal as the tail lights (black wire). This is incorrect; the brake switch should be HAT - hot at all times - connected to the same terminal as the generator wire (yellow).
 
I stand corrected. Thanks Y-Blockhead. I was just trying to deduct from the symptoms the original post said that they only worked when the headlights were on.
Eric
 
thanks Badpuppy....i used the multimeter to check voltage across the brake light switch and got nothing; funny thing...when i touched the brake light switch, half of it fell off while half of the empty switch shell was still bolted on. The switch itself was full of goo (grease and dirt). ordered a new one from A&L but i suspect there are some wiring anomalies since the ammeter on the dash appears to be wired in reverse...meaning when the lights are turned on, it shows charging. I love this car and a good puzzle...will keep you posted. thanks for the support which helps me venture out to where i haven't been before!!
 
Ammeter. Is the car 6v or 12v ? How is the battery hooked up, - or + grd ? Alternator or generator ? Once we know that we can figure out the ammeter issue, it'll be easy. It may just need a flash/polarizing.
 
OK, does it show a charge when running at a fast idle ? I should have asked that before.
With engine running, jump across the cut-out terminals for a second. Then see if the ammeter is correct. If correct, with the fan belt loose, applying power to the generator will cause it to motor slowly in the correct rotation [CW from front]. If this corrects it, fine. And it probably will. If the ammeter reads backwards in everything, charge with lights on and discharge when running, then the wires on the ammeter need to be switched.
 
Generator should be polarized with engine NOT running, to align it with battery polarity. But probably not the cause. Ammeter wire reversal is a common problem for some reason. Just hook it up per Janke's diagrams on the mafca site.
 
I appreciate everyone's help and I will take all your helpful input into my troubleshooting process. I will update this thread after i receive some new parts and i can check things out.
Thanks again,
Carol ann
 
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