Puzzle: Alt light comes on when parking brake not engaged???
08-04-2013, 08:36 PM
#1
Thread Starter
Join Date: Mar 2007
Location: na
Posts: 40
Puzzle: Alt light comes on when parking brake not engaged???
Wow this is going to sound crazy but, here it is...
1971 Boss 351 clone (351, 4spd)
If both of the following conditions are met, the alternator light will come on but not always immediately.
1- Headlights and/or parking lights are on.
2- Apply normal brakes.
-> Now here's the rub.. Partially engaging the Parking Brake (hand brake) "solves" the problem. Release Parking Brake and the problem comes back.
Another way to get the Alt light to come off once it's lit, is to turn off the lights. Now I can turn the lights back on again and it will be ok until the normal brakes are re-applied.
Other relevant info:
-Vehicle is NOT equiped with Parking Brake indicator light, thus there is no switch at the parking brake pedal.
- Issue began suddenly without warning.
- All light bulb sockets at rear of car have been checked and cleaned.
- No wire is stuck in the Parking Brake pedal mechanism or otherwise interfere with it(which could cause short circuit).
- No wire is interfering with Parking Brake cable under the car.
- Disconnecting the Proportional valve switch has no effect.
- Removing all light bulbs at rear of car has no effect.
I'm running out of ideas... Can anyone help solve this??? Please read carefully before answering anything. The above info is very specific and believed to be accurate, though it doesn't seem to make any sense..
1971 Boss 351 clone (351, 4spd)
If both of the following conditions are met, the alternator light will come on but not always immediately.
1- Headlights and/or parking lights are on.
2- Apply normal brakes.
-> Now here's the rub.. Partially engaging the Parking Brake (hand brake) "solves" the problem. Release Parking Brake and the problem comes back.
Another way to get the Alt light to come off once it's lit, is to turn off the lights. Now I can turn the lights back on again and it will be ok until the normal brakes are re-applied.
Other relevant info:
-Vehicle is NOT equiped with Parking Brake indicator light, thus there is no switch at the parking brake pedal.
- Issue began suddenly without warning.
- All light bulb sockets at rear of car have been checked and cleaned.
- No wire is stuck in the Parking Brake pedal mechanism or otherwise interfere with it(which could cause short circuit).
- No wire is interfering with Parking Brake cable under the car.
- Disconnecting the Proportional valve switch has no effect.
- Removing all light bulbs at rear of car has no effect.
I'm running out of ideas... Can anyone help solve this??? Please read carefully before answering anything. The above info is very specific and believed to be accurate, though it doesn't seem to make any sense..
Last edited by GinaX; 08-04-2013 at 08:39 PM.
08-05-2013, 10:54 AM
#2
1st Gear Member
Join Date: Apr 2012
Location: Louisiana
Posts: 134
Ok, I'll bite.
1. Has any work been done recently on the car? no matter how insignificant to the problem?
2. Have you tested the alt? tried a new volt/reg?
3. Checked the engine-to-body ground?
(I had a similar issue back in the day, only mine was intermittent with the shifter rubbing the console insert)
Something is going on down there with the parking brake.
Here's my theory (which is worthless without seeing the car). The partially engaged parking brake is making a more solid ground somehow.
The fact that removing the bulbs doesn't make it go away shows me that it's not an amp draw problem.
The wiring on these old cars is pretty simple.
Start trouble shooting the basics from square 1.
Hope this helps.
Keep us updated on what you find.
1. Has any work been done recently on the car? no matter how insignificant to the problem?
2. Have you tested the alt? tried a new volt/reg?
3. Checked the engine-to-body ground?
(I had a similar issue back in the day, only mine was intermittent with the shifter rubbing the console insert)
Something is going on down there with the parking brake.
Here's my theory (which is worthless without seeing the car). The partially engaged parking brake is making a more solid ground somehow.
The fact that removing the bulbs doesn't make it go away shows me that it's not an amp draw problem.
The wiring on these old cars is pretty simple.
Start trouble shooting the basics from square 1.
Hope this helps.
Keep us updated on what you find.
08-05-2013, 12:21 PM
#3
Thread Starter
Join Date: Mar 2007
Location: na
Posts: 40
Thanks for your reply. The alternator was replaced a few months prior to the problem showing up. Nothing else was done to the car since. I'm very baffled about the fact that pressing the Parking Brake ever so slighly makes the issue go away. I spent hours under the dash trying to see what can be the reason, even removed the air vent so I can see better. There is positively nothing in the way of wires touching anything. I've also tried just pulling the cable directly with long noze wisegrip and it worked.
Now that you mention it, I too suspect a better ground with the PB engaged for some reason, maybe on some other part of the car. The reason I replaced the alternator before was that, with the old one the alt light would come on with the headlights but very faint (the alt light was on but very dimmed). I guess the new and stronger alternator helped fix the problem for a while, and now the alt light comes on strong but maybe still the same problem as before. Thanks again for your help, I think you're on to someting. Cheerz
Now that you mention it, I too suspect a better ground with the PB engaged for some reason, maybe on some other part of the car. The reason I replaced the alternator before was that, with the old one the alt light would come on with the headlights but very faint (the alt light was on but very dimmed). I guess the new and stronger alternator helped fix the problem for a while, and now the alt light comes on strong but maybe still the same problem as before. Thanks again for your help, I think you're on to someting. Cheerz
Last edited by GinaX; 08-05-2013 at 12:43 PM.
08-07-2013, 04:16 PM
#5
Thread Starter
Join Date: Mar 2007
Location: na
Posts: 40
I just checked the charging today. Using my very cheap voltmeter, I get 13v at the battery when the engine is not running. When the engine is running I get +/- 16v. When I turn on the headlights it drops to +/- 15v. So assuming my voltmeter is faulty, I probably have a 14-15v charge. The engine idles pretty fast so there is no difference whether it is idling or not.
I noticed something different today. Maybe I did something. It used to be that the headlights or the parking lights needed to be on for the alt light to come on. No longer the case. Now I've seen the alt light come full-on-red just for applying the normal brakes. But as usual, I just engage the parking brake one notch (just so the pedal doesn't come back up) and the problem goes away. As a matter of fact, I only need to press the parking brake pedal less than half an inch and the problem goes away.
I noticed something different today. Maybe I did something. It used to be that the headlights or the parking lights needed to be on for the alt light to come on. No longer the case. Now I've seen the alt light come full-on-red just for applying the normal brakes. But as usual, I just engage the parking brake one notch (just so the pedal doesn't come back up) and the problem goes away. As a matter of fact, I only need to press the parking brake pedal less than half an inch and the problem goes away.
08-07-2013, 09:07 PM
#6
Moderator
Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
Hopefully you do have a bad volt meter and not a bad voltage regulator. I would test that volt meter on a known voltage for example a new AA battery...it should read about 1.7v. even a cheep meter can be precise. Voltage regulators can fail and allow unregulated full field power to run through the system which increases with rpm with no cap and can easily exceed 17v...Over charging the battery and damaging electrical components.
Grounds can be sketchy on older vehicles. Your light issue could be due to a ground problem. A simple test is to get a 2' piece of wire say 12awg and run it to a nice clean raw piece of metal on the engine block say a carb bolt or intake bolt. Then run the wire to a nice clean frame ground say on the fire wall or any clean bolt on the frame. Alligator clips can be used for testing purposes. See if doing this changes anything.
-Gun
Grounds can be sketchy on older vehicles. Your light issue could be due to a ground problem. A simple test is to get a 2' piece of wire say 12awg and run it to a nice clean raw piece of metal on the engine block say a carb bolt or intake bolt. Then run the wire to a nice clean frame ground say on the fire wall or any clean bolt on the frame. Alligator clips can be used for testing purposes. See if doing this changes anything.
-Gun
08-08-2013, 01:45 PM
#7
Thread Starter
Join Date: Mar 2007
Location: na
Posts: 40
Thanks for very useful advices. I tested my meter with various type of batteries and it wasn't lying. So I proceeded to replace the voltgage regulator on the car. This resolved the alt light problem and charge is 14v. Now the light never comes on anymore no matter what, except of course upon engine startup.
However, I'm pretty sure there is still a grounding issue, because the direction signals (flashers) blink faster when the parking brake pedal is pushed (as previously explained). So that will be the next step, figuring out what to ground with what? I try to avoid getting under the hood, because this is a residential area and apparently women shouldn't be fixing cars lol
But this was definitely a step in the right direction and I'm very happy about it. Cheerz
However, I'm pretty sure there is still a grounding issue, because the direction signals (flashers) blink faster when the parking brake pedal is pushed (as previously explained). So that will be the next step, figuring out what to ground with what? I try to avoid getting under the hood, because this is a residential area and apparently women shouldn't be fixing cars lol
But this was definitely a step in the right direction and I'm very happy about it. Cheerz
Last edited by GinaX; 08-08-2013 at 02:09 PM.
08-08-2013, 09:09 PM
#8
Moderator
Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
Holy s***!
I think you are the first person who, since 2005 has actually taken my advice, run the testing methods I suggested and actually solved the problem as a result of doing so...........
You need to ground the engine to the frame...use something similar to what I described above to test or you could simply purchase a ground strap from summit and try it...wont hurt anything.
-Gun
I think you are the first person who, since 2005 has actually taken my advice, run the testing methods I suggested and actually solved the problem as a result of doing so...........
You need to ground the engine to the frame...use something similar to what I described above to test or you could simply purchase a ground strap from summit and try it...wont hurt anything.
-Gun
Last edited by Gun Jam; 08-08-2013 at 09:31 PM.
08-09-2013, 05:00 PM
#9
Thread Starter
Join Date: Mar 2007
Location: na
Posts: 40
LOL Maybe some people are too proud to follow advices or admit that they did. Once again, I just did what you've said, grounded the engine to the car (the little ground wire from the battery looked pretty weak btw). Now my issue is completely fixed. Everything works better in the car too, the flashers blink fast, the wipers are quicker, etc. I can turn everything on at once with the heater and the headlights, there is enough juice for everything, and I never see that alt light anymore. And guess what?? I don't have to press the parking brake pedal LOL. Who would've thought? You were great, straight to the point... just the kind of auto-mechanic I'd like to have. Thanks a million. hi5