Protege electrical problem

My friend’s left her car (1994 Mazda Protege) without starting it for about 6 weeks while she was away. When she came back it needed to get jumped to start.

After that she drove it for a couple days. There was also a new problem with the stereo that had never occured before: quiet static out of the speakers while the stereo was turned off. Then when she put the faceplate on the stereo (after market stereo, btw), there would be a loud whining sound. Once the stereo was turned on, no problems.

She then left the car for four days while camping, came back and had to get it jumped again.

It seems that if the car runs at least once every day or two it’s fine, otherwise she needs to get it jumped.

So far to try to discover the source of the problem we’ve:

Checked voltage across the battery when stopped. It was around 12.6 v I believe.

Checked voltage across the battery while running. It was about 13.8 v.

Here’s where it gets embarassing:
With the car stopped, we disconnected the battery and checked the current (with a Fluke 77 multimeter). Got a reading of 3.6, with a small DC on the right of the display. Now I’ve never been very good with electrical analysis, but shouldn’t it have been displaying something along the lines of x amps, or milliamps, etc.? Anyway, pulled fuses one by one, didn’t get any change in the reading.

Basically, I’ve got no idea what could be causing this.

Could anyone please suggest ways to find the problem, or have ideas as to what it could be?

BTW, if anyone were able to instruct me on how to make an amperage measurement with a Fluke 77, I’d greatly appreciate it. Thought I had it set up right, but when we reversed the electrodes the reading didn’t simply go from positive to negative, it went from 3.6 to -9.4. A little strange, to say the least.

There’s definitely a short in the system someplace. I’m pretty sure that reading means 3.6 amps DC, which is a pretty good load on the battery. If pulling fuses didn’t isolate the problem, then it must be in the primary electrical system. Trace the positive batterr cable back to the starter. Inspect it carefully the whole length for nicks, frays, or melted insulation. Trace the other, thinner positive battery wire back to the fuseblock, and inspect for the same things. That’s a start.

Sounds like you might have a ground in the system, if the battery is bleeding off. Then again, the battery may have just gone dead. You don’t say whether or not this is a maintenance-free battery; if not, have you checked the electrolyte levels? You could also have a faulty alternator, although if it’s gone bad, the car will generally not start at all without assistance.

I’m not sure you should get any significant current reading with the battery disconnected. Amperage is load; if the engine is not running and nothing is turned on, then no load should exist. But perhaps I’m misreading your post.

A problem I had with my Toyota was that after sitting for an extended period, the starter contacts became corroded and I had trouble starting it. After starting several times, the problem finally went away.

Are you breaking the circuit to take readings and measuring across the break, and if not, how are you doing it?

To test the load on the battery, we disconnected the positive terminal, then connected the multimeter, which was set to DC amps, between the positive terminal on the battery and the positive cable.

This seems to me to be the proper way to test it, but then I just don’t know why it would switch between 3.6 and -9.4 A when we reversed the leads on the multimeter.

By testing like this while pulling fuses we were hoping to find a single fuse that would change the reading from 3.6 to near 0. If I’m right, I’d expect in a car without problems and everything off there should be no more than a couple milliamps going through, just enough to keep the security system going and the clock.

Thanks for all the quick replies, any more ideas would be greatly appreciated. We’re going to have a closer look at it tonight, let you know how things go.

Who installed the stereo?

It sounds like there was no original stereo harness and whoever installed this one has bypassed the accessory lock on the ignition…

When you measure DC amps with the multimeter you must do two things:

  • Move the selector switch to the DC amps settings (that’s the A mark with the with the two straight lines over it, one line solid and the other dashed)

  • Move the red lead on the meter from the normal connector to one of the amperage connectors.

The normal connector for the red lead is for measuring Volts, resistance, and continuity. So it’s marked with the V (for volts), the ohm sign (upside down horseshoe), and the diode symbol (a line with a little arrowhead pointing to one side).

The amperage connectors (the Fluke 77 has two) are marked 300 mA and 10A. The 300 mA connector is for a max of 300 milliamps (about a third of an amp) or 10 amps max.

So leave the black lead in the Com connector, and move the red lead to the 10A connector. Select the DC amp setting on the selector dial. Remove one cable from the battery and connect the red to that and the black lead to the now empty battery terminal. You should be able to read any current flowing through the meter. Reversing the red and black leads should reverse the sign of the reading, but not the amplitude.

If the reading is too low with the red lead in the 10A connector, move it to the 300mA connector and try again.

Thank you all, sounds like I’m going to be able to give this a better shot at testing tonight.

Thanks RJKUgly, I’m not positive we had the leads hooked to the multimeter properly. I think we did, but it’s definitly worth checking. BTW, I tried the Fluke site for a manual, nice site, but they don’t have online manuals for older products.

dutchboy208, would it be possible for you to explain what the accessory lock is? Am I correct in assuming it would be the portion of the switch at the ignition that should connect/disconnect the stereo from power?

If it is, I have a feeling it is connected properly. I can see how it could cause these problems if the stereo wasn’t connected to the accessory lock correctly, but I imagine we would have noticed the static and such earlier (the stereo’s been in the car at least a year and a half with no problems).

Is there any simple way for me to check if the stereo’s wired correctly through the accessory lock? Would checking for voltage at the stereo when the car’s off work?

Thank you all, you’ve definitly given me some work for the evening.

While I don’t work with a 77, I work and teach on 73s,75s, and 78s. The amperage reading should read the same with the leads reversed, only the sign will change. Based on this post, you did not have the leads hooked up correctly. RJKUgly gave as good a description of how to hook up a Fluke meter as you will find, so I won’t go back over that.
I will add this one very important warning
As soon as you get done measuring amperage remove the red lead from the amp socket on the meter and replace it in the voltage socket. if you forget to do this and you go to measure voltage you will blow the internal fuse in the meter in about 0.nothing seconds. (Every, and I do mean every electrical fault tracing class I teach, somebody goes brain dead and does this. I buy fuses by the dozen.)

Thanks for all the replies. Last night I wasn’t able to look at the car as I’d hoped, so she’s taken it into a garage this morning.

Really wish I would’ve had a chance to look it over again, but at least it’s getting taken care of. I’ll post back with whatever it turns out to be.

Admit it. You’ve done this too, i know you have. We’ve all done this at least once.

Somewhat OT: I did something similar once as a co-op: I was working on a board and wanted to measure the waveform across a resistor. So I grabbed a scope and connected the probe’s center lead to one side of the resistor and the scope’s common lead to the other side of the resistor.

Smoke. :frowning:

What an idiot. For some reason I thought a scope had a differential or floating input stage. I didn’t realize that it was single-ended & ground-referenced, and that I would be grounding whatever I connected the scope’s common lead to.

This wouldn’t have happened if the board or scope had been isolated. I now know better.

Yep. That’s why at my transformer-manufacturing-and-testing job we had all our scopes connected through three-to-two prong adaptors so that the ground would float deliberately. I nearly smoked a Tek 485 by forgetting to plug that adaptor in once.

That will work, but you must be careful, since the entire scope could be floating at a high voltage.

Well, this is kind of interesting… She got the car back today and was told that the stereo was hooked up to draw its power from the interior lights. I didn’t get to talk to them to get any more information, so this is a little sketchy.

She didn’t want to spend the money to have the stereo put back in right now, so currently it’s disconnected.

Now possibly this is just my inexperience with car electrical systems, but if it were indeed hooked up to the interior lights, wouldn’t that be pretty obvious? Wouldn’t that mean that the stereo would only be on when the interior lights were on?

When the stereo was installed, it was hooked up to the factory wire harness that the original stereo had been hooked up to. No new wires were run. I just have no idea how it could have made it to the interior lights.

Could anyone possibly explain this one to me? Or is there another more probable cause?

Well I’ve only done it once when I was teaching…

As a tech I did it, ah well, let’s just say more than once.

Getting back to the OP most stereo have two power inputs. One should be live all the time, and one that is switched or hot with the key in the acessory or on position.
The hot all the time lead is for the clock, and memory functions of the radio. The switched lead is what the radio uses for power.
The memory lead could very well be hooked to the dome light circuit since in most cars that is in fact hot all the time (the switch on the door supplies a ground) The draw on the memory lead is in the very low milliamp range. No way could this be causing the battery going dead.
However if there was a fault in the radio, then maybe that could be the problem.
BTW have you had the battery tested? And recharged?
Your stereo issuse might be a result of a problem elsewhere in the electrical system.

The information presented doesn’t all make sense to me.

The static in the speakers and whining with the faceplate on, mentioned in the OP, suggest an internal problem with the stereo. Since these symptoms occurred with the stereo turned off, they also suggest a possibly significant power drain that could occur when the car is off. Right now I’d say that’s the most likely explanation for the battery going down when sitting for a couple of days.

Besides the main power to the stereo, which is switched through the ignition, there is a memory power feed which is unswitched (in other words, always connected to the battery). So if the stereo had an internal fault using some power, it could indeed drain the battery.

Many cars have a panel light feed to the radio, which illuminates its controls when the park/tail or headlights are on. I assume this is what was meant by “interior lights.” But if this were used as the main power feed to the stereo, the stereo would only work when those lights were switched on. Presumably this was not the case, since that wasn’t mentioned as a symptom. Regardless, I just can’t make any logical connection between the stereo’s power feed coming through the panel light circuit and the battery drain problem.

Now, if by “interior lights,” they mean courtesy/dome lights, that is an unswitched circuit. If the stereo main power feed came through there, the unit would turn on even with the ignition off. But if the stereo were shut off when the car was shut off, that wouldn’t really matter.

What I understand from the info given is that there were no problems with the stereo operation or the battery going down until the car sat for 6 weeks. Assuming the wiring to the stereo was not changed during that time, it’s hard to imagine how said wiring could be causing a problem now when it wasn’t causing a problem months ago.

It just doesn’t all add up. And I have no clue as to what relation, if any, there might be between the car sitting for weeks and the onset of problems. Several pieces of this puzzle seem to be missing.

Oh no, not me, never.

Those spare fuses I carry are for… for… for other people I might run into using the same meter. Yeah, for other people, that’s it. :slight_smile: