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Help, Electrical Problems.....

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Old March 15th 09, 06:55 PM posted to rec.audio.car
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Posts: 810
Default Also.....

First, thank you for the advice MG, I truly always appreciate any help I can

Yes, a grounding problem has occured to me, but here's the thing: the yellow
B+ wire is giving me 13 volts when I use the factory ground in the dash.
Yet when I touch the red ignition wire to one of my multimeter probes and
the black probe to that same factory ground I get .67 volts (when the car is
running). See what I'm getting at? If the radio's factory ground is giving
me 13 volts with the one B+ wire and then using the same ground, .67 with
another positive wire, doesn't that mean the problem MUST be with the
positive ignition wire?

In other words, if I had a ground problem with the factory ground in the
radio cavity, I would likely exhbit problems with any positive wire I

Now, are you talking about grounds under my hood? If so, I again took out
my trusty multimeter, and touched one probe to the positve battery terminal
with the other probe to the frame of the car and engine block. The voltage
potentials were negligable (.02 volts). I also tried touching one end of
the probe to the engine block and the other to the chassis, again I read a
very negligable .02 volts as the difference in negative voltage potentials.

Grounds are amost always the first place I look when I am having stereo
problems so just applied that same knowledge to this issue. IN FACT, I had
even expected that this might be the cause and so EVEN BEFORE I tested it I,
quickly built (with spare wire I had) two 4 foot lengths of 4 guage cable
to run from the neg. battery post to the car's chassis, and the other cable
would likely run from the engine block to the car's chassis.

I have done this little trick in the past with several cars and usually gain
about .1-.3 volts at my amps when cranking them.

Everyone always focuses on the positive side, but neglects the negative
side, forgetting that voltage is NOT a measure of electrical flow (like
watts), but a measure of voltage potential differnces and that you can
increase voltage by, of course, raising the positive side, but also by
lowering the negitive side.

Anyway, long response to **** you probably already know. But again I don't
think it's a ground issue as I am using the same ground for both the B+
(which gives me a nice happy 13 volts) and ignition wire.

But I am no EE and if anything I have written is wrong, if there's something
else I can try or might help this problem
PLEASE, PLEASE let me know.

For instance, how might I back-track the ignition wire to find the problem?
IS this something I can do? If all fuses check out, based on everything I
have written I could really use some ideas here. You said you didn't see my
other messages, I'll copy them to this so you get a more accurate picture of
what the car is doing.


Nick - see attached below

Hey Guys!!! How's it hanging? Now I know an awful lot about car audio and
the nature of voltage, amperage, watts, ect.

But I don't know much about the complexity of a car's electrical system and
that is EXACTLY the problem I'm having.

The car is a 1989 Mazda MX-6, it's my wife's car, and we recently had some
problems with it stalling, missing, and even dying sometimes. So after
doing all the things I know how to do (changing air filter, fuel filter,
plugs, wires, and several other things) I took it to a "shade tree" mechanic
who lives very close to us. I should say now that she had a simple system
in her car that consited of only a Pioneer HU and some after market BA
speakers (she listens to talk radio so there was really no point in building
her a big system, even though I have a spare amp and sub just sitting
around, I had to twist her arm just to put in the Pioneer and Boston
speaks), that system worked fine up until we took it to this mechanic.

When we got the car back, we found he had needed to replace the distributor,
cap, rotor, and coil. The car ran fine once again however the weird thing
is that the Pioneer deck no longer came on. So I took the dash apart and
started checking things with my multimeter (oh, I should say that the VERY
FIRST thing I did was check all the fuses which were fine). The B+ voltage
was fine, as was the ground. But the red ignition wire was reading .64
volts when the car was on OR OFF. So I said to myself, fine, I'll find
another 12 volt source that turns off when the key is turned off. I checked
the ciggarette lighter wire and every other wire I could find.

No dice. Although the yellow B+ wire seems to be fine, the ignition wire
(or any other wire that should produce 12 volts when the key is turned) is
only producing .64 volts whether the key is turned or not.

Help!!!! I've never come accross this type of problem before. Obviously it
has something to do with the car's ignition system (I think) but I have no
idea where to look for the fault. Like I said, the car runs great. Also,
again the radio had worked fine in the past using the red ignition wire as
my "turn-on" wire. Now only the yellow B+ wire is the only wire I can find
in that cavity that produces 12 volts, and of course it produces those 12
volts whether the key is turned on or not.

I really need some help here. Maybe even a work around as the car appears
to run just fine yet something is clearly wrong but does not seem to be
effecting the performance of the car.

Thank you in advance,

Beyond that, I can only offer workarounds. For example, installing a
toggle switch in a discreet location (like a 2nd "on/off" switch) for
the head unit, and basically running it off of the same constant power
wire that the deck is already using.

Thanks Lull, in fact that is EXACTLY what I am doing for now. I cut the red
ignition wire, twisted the yellow B+ and deck's ignition wire together and
so the radio works fine, you just have to remember to turn it on and most
importantly, OFF again when you are done. Like I said, I cut the red
ignition wire (and crimped the ends) so no current can flow back from the B+
into the ignition system.

But as you apptly put it, I have a larger issue I need to resolve as most of
my dash lights currently don't work (and they did before), cigarrette
lighter does not get any power, ect. I know all these problems are related
in some way.

I did check ALL the fuses in the fuse box in the cabin. Are you saying (and
please excuse my ignorance, I really don't know much about car electronics)
that there is another bank of fuses under the hood? If so, one of those
could be blown and be the source of my power problems.

It's strange. You would think that if the ignition wire was sitting at only
..64 volts there might be engine problems still, but there is not. It runs

This one really has me baffled. Again, thanks for the reply, Lull. Talk to
you later...

I just now got my multimeter out and set it to 200 ohms. When the probes
are not touching I get no reading at all. When the probes touch each other
OR touch each blade of a blade fuse I get a .5 ohm reading. I just now went
out to my car and tested every fuse, they all seemed fine as I got the .5
ohm reading.

So it does not appear that I have a bad fuse as now I have electricaly
tested them as well as visually tested them.

Man, this one really has me stumped. Again, the engine starts and runs
perfectly. Yet obviously something is seriously wrong with my electrical
system as about half of the dash lights do not work (fortunately all the
intrument cluster lights do work). But the instrument cluster lights are
about the only lights that DO work. The ciggarrette light does not work
(nor do I get power to the cigarette lighter), the heater lights don't work
and the shifting lights do not work. Yet all of these had worked before.

Also, the battery and alternator appear to be fine as I just checked that.
I was getting 14.4 from the battery.



"MG" > wrote in message
> "MOSFET" > wrote in message
> m...
>> My check engine light winks at me now and then, but never stays on more
>> than 5 seconds or so. The car had just been tuned up and as I said
>> before, it runs perfectly (no missing, no loss of power, on stalling, no
>> trouble starting, and it idles very, very smoothly for a four banger).
>> I have to think that the check engine light MUST be related to this
>> electrical/voltage problem somehow as every other mechanical system
>> checks out fine.>
>> Part of my wants to take it to a reputable automotive repair service and
>> have them diagnois the problem. But another part of me figures that as
>> long as it is running well and I can do work-arounds to get the stereo
>> working, why spend the money? Especially in light of the fact I have
>> just paid this other mechanic $500 to replace the distributor, cap,
>> rotor, coil and give it a full tune-up.
>> The problem is, I discovered through working with him he is kind of a
>> jerk and there is no sort of gaurentee. So if I take it back to him,
>> it's not likely (in fact I'm sure it's not likely) that he will give me
>> any kind of discount to help discover the problem with the ignition
>> voltage. I think I will just keep trying different things and doing more
>> research (I need to buy a Haines manual) and see if I can stumble onto
>> the problem. I actually enjoy this kind of car-detective work.
>> But after a two or three more weeks of this, if I have not found the
>> problem I will take it into my old tried and trusted car-repair shop.
>> You see, my BIG concern revolves around the fact that if this particular
>> electrical system is not working correctly, might it effect others down
>> the road? I don't want to have to find out the hard way.
>> Thanks,
>> Nick

> I missed the first part of this, but have you checked all the grounds? A
> loose ground somewhere could have this sort of effect.
> mg

Old March 15th 09, 07:03 PM posted to rec.audio.car
external usenet poster
Posts: 810
Default Correction on last Email

"Now, are you talking about grounds under my hood? If so, I again took out
my trusty multimeter, and touched one probe to the POSITIVE BATTERY terminal
with the other probe to the frame of the car and engine block."

It should read "one probe to the NEGATIVE battery terminal....."



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