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  #1  
Old 10-15-2008, 12:45 PM
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Location: Vancouver, BC
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Electrical Woes

So, something is going on with my car. Here's what I have seen so far, just beginning today.

1) On the weekend, I dropped the driver's kick panel to look around for the cruise control brain. I found it, but was not able to find a good way to get it out so left it in.

2) I also have a third party electric brake controller mounted ,for use with my towing hitch (to be honest, the wiring job on it doesn't look so great). I inherited this from the previous (original) owner

3) Today while driving in to work, I was about 3/4 of the way there when I noticed my brake light and battery light started weakly glowing. At the time when they did start to glow, I was idling, headlights off, blower off, but my radio on. I killed the radio, no change. Once I started driving again (not just idling at a stop light) the problem resolved itself for about 30 seconds, and then came back, and then went away again.

4) I parked at work, and turned the car off. When I tried to turn it on again, I noticed that while I can start it, not all of the usual warning lights come on - in particular, neither brake warning light comes on, and the battery light doesn't come on either.

5) I can start without any problem

6) The LED display of my brake controller is now illuminated even when the car is turned off.

So I am not entirely sure what is going on. For sure I must have some kind of a short in the lousy wiring of my brake controller. I am seriously considering tearing that thing out when I get home - or at least disconnecting the system from the battery. I'm not sure if that is my whole problem, though. Could my alternator be going? The alternator's voltage regulator? I don't mind fixing either, but I am not sure where to start.

Any help / advice? I sure hope I can start my car to get home today.
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  #2  
Old 10-15-2008, 01:00 PM
92 300D 2.5L OBK #59
 
Join Date: Feb 2007
Location: Central FL
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Start with the easy stuff.

Check your fuses first.
Disconnect your controller from the battery if its easy.
Check Battery Voltage and charging voltage.

When you first turn the key to the on position, do all the lights warning lights come on (they should unless they're burned out)

Its a start....
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  #3  
Old 10-15-2008, 01:03 PM
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Yeah, I am going to disconnect the controller over lunch. I have not checked my fuses, but I will have a look.

No, not all my warning lights come on when I turn the key. The ones that do NOT come on:

1) Battery Warning Light
2) Brake Wear Light
3) Brake Reservoir Light

but my glowplug light and seatbelt light DO come on.

When I left the house this morning, all were in working order.
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Old 10-15-2008, 01:03 PM
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There may be a shorted/weak diode in your alternator and the brake controller is the "path of least resistance" which is why the light on the controller stays on with the engine off. The easiest way to check is to start the car and place a meter across the battery terminals. First, in VDC mode you should see ~13.5 volts right after start-up. Second, in VAC mode you should see <1 volt, if more a diode in the alternator is going out.
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  #5  
Old 10-15-2008, 01:07 PM
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I can certainly check that out when I get home (no multimeter at the office, doh).
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  #6  
Old 10-15-2008, 01:18 PM
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Actually, I should have something on this soon! I did track down my multimeter after all. Getting that brake controller disconnected is probably my best first step, seems like, in addition to fuses and testing the alternator.
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  #7  
Old 10-15-2008, 04:41 PM
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Ok - I have an update on this!

I went out today with my multimeter, and sad news. When the car is off, the batter reads 12.8 Volts - seems pretty sane.

After I start the car, I test the voltage at the battery's terminals, while the car is idling and no loads on the system, 12.4 volts. Checking for AC and I see 0.1 volts.

Nothing is any different with the electrical brake controller disconnected from the system.

If I add a load, like my headlights, I see a small drop, down to about 12.3 volts.

No fuses are blown, either.

Help! What should I do? I'm getting worried that pretty soon I will find myself unable to start the car and I need it as my daily driver. I'm leaning heavily towards just taking it to my local specialist (for those of you in the Vancouver area, Henneken AUto).
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  #8  
Old 10-15-2008, 07:10 PM
92 300D 2.5L OBK #59
 
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On the way home stop by Your local parts place that offers free alternator checks. Sounds like alternator or voltage regulator.
Not too major a problem. You'll be able to do it.
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  #9  
Old 10-15-2008, 11:43 PM
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Well, it's at the shop now (much as I would love to do this myself, I have not got the spare time this week to do it) - but their head mechanic (who comes to me very highly recommended) seems to confirm that I am looking at an alternator or maybe regulator problem. Fingers crossed!
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  #10  
Old 10-16-2008, 12:30 PM
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Quote:
Originally Posted by xdjio View Post
.........After I start the car, I test the voltage at the battery's terminals, while the car is idling and no loads on the system, 12.4 volts. Checking for AC and I see 0.1 volts.

Help! What should I do? ................
I wish we could have seen the results earlier, before you went to the expense of taking it to a shop. However, your meter readings tell the story:
The alternator is really pretty simple and hopefully I can do a satisfactory job of explanation and maybe help you, and others, in the future.

First, mechanical-to-electrical is simply some windings spun real fast next to magnets and the output is AC volts.
Second, AC-to-DC is the use of diodes to rectify the current to DC.
Third, Regulation controls the voltage level to about 13 to 13.7 Volts DC.

So when troubleshooting, check for Volts AC tells us whether the diodes are OK. Then the check for Volts DC tells us whether the regulator is controlling the voltage OK.

From your readings, this tells us that the likely failure is the regulator. As you can tell from photos of the regulator, it uses spring-loaded brushes which contact the comutator (the spinning part). Both the brushes and comutator wear and, depending on factors, in many cases the regulator can be changed several times to renew the alternator.
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