"Hidden" electrical drainage problem
 

HI FOLKES--
I have been plagued by a long-time problem on my "96 SVX that no shops seem to be able to solve:

• Sometimes, when I go to start my car in the morning the battery will be dead or almost dead. I then have to use my battery charger to get it started. The car seems to be OK for a while after this.

• Sometimes this problem also happens after I have just been using the car (and have turned it off briefly) and then it won't start it again.

The battery, alternator and starter are all fine.

MY GUESS: I think there is a hidden short-circuit somewhere in the car’s electrical system. But the Subaru dealer's shop says they cannot detect any "short-to-ground" problems.

What can I do to get this problem diagnosed?? Any ideas are appreciated.

gary96SVX

Use a multimeter set to measure current (Amps or Milliamps). Pull the fuses one at a time and stick the multimeter probes into the fuse holder. This will tell you how much current each circuit is using. The circuits drawing the most current are the most likely candidates for your fault.

If this is the only symptom you had then your guess would be a good one. But, unfortunately you go on to say :

Which, of course, throws the whole thing into confusion.

So do some logical testing.

1. Beg, borrow or steal a multimeter.

2. With everything turned off inside the car and the doors closed etc. etc. remove the negative terminal from the car battery. With the multimeter on a high current range, put the negative lead of the multimeter on the battery negative terminal and the positive lead of the multimeter on the negative battery lead.

3. With luck the meter will show little or no reading. Slowly switch the multimeter to lower and lower current ranges until you get an appreciable meter reading. With luck you will find that you have a current of less than 250 milliamps flowing, less is better. An appreciably higher reading than this could conceivably flatten your battery overnight, if it's in a poor state of charge, and if the car is left for a week or longer then this could definitely cause problems.

4. If you are showing a high current then pull and replace the fuses one at a time until the problem is isolated to a particular fuse. Then you can chase down the problem in the equipment fed from that fuse; it could be a defective switch, chafed wiring etc. etc. Always suspect aftermarket additions, especially if you did not fit them yourself.

If everything is fine at this point but your starting problems remain then.

1. Clean up both battery terminals.

2. With the engine off, measure the battery voltage with the mutimeter set to measure on the 20 volt range or similar, at the teminals themselves, not the leads, but leave the leads connected.

3.A rough rule of thumb: 13 volts or more -fully charged 12.8 volts - good, 12.5 volts - pretty nearly flat.

4. You'll need an assistant for this bit. Get your assistant to use the starter
and watch the battery voltage on the meter. If all is well the battery voltage will drop as the car cranks, but the car will start. The better the battery is, and the higher its state of charge, the less voltage drop you will see, anything more than a couple of volts is suspect, but if the car starts then this is obviously not your immediate problem.

If the car does not crank or only cranks over slowly, and the voltage hardly drops at all, then the problem likely to be in the wiring between the battery and the starter. Check all the connections, including the factory made ones between the wiring and the connecting lugs.

I could go on - probably forever:)

The thing to remember is that without taking measurements with a meter, fixing this problem is going to be difficult, you will probably have to keep replacing parts (many of which are perfectly serviceable) until the problem goes away, and you will have learned absolutely nothing in the process whilst simultaneously wasting time and money.

Get a multimeter, and a good book on automotive elecctrical systems, or have a thresh around on Google, and educate yourself.

Have fun too.

Pete.

If you hear a click but the engine doesn't turn, try this; put the shift gear into neutral and try cranking the engine. If this works, then you have the same problem that most of use have- a bad neutral safety switch or a bad ignition switch. Due a search on Starter Bypass Relay Install . Good luck.