I have a weird electrical problem . . .

"Every time I open the door, the wipers flap once OR I have the weirdest electrical problem."

No matter what kind of electrical symptoms you may have, the repair procedure is exactly the same."

You must pay a repair shop $45-85 to have them test your electrical system. They will :

Test the battery and charge it if needed,

test the alternator volts (13.4 to 14.8 volts for Domestic vehicles or 13.4 to 15.5 volts for Import vehicles at idle, all accessories off),

test the alternator amp output (10-30 amps at idle, 30-250 amps at 2,000 rpm or so, all accessories off),

test the alternator diode pattern, a mandatory test done with alternator in the car) and

test the starter draw both cold and hot (150-200 amp draw engine cold or 350-500 amp draw engine hot.

Who can run this test? - All general repair shops, gas stations and dealerships can run this test. You can get many auto parts stores to perform some portion of this test for free, but NEVER take the alternator or battery out and have them bench tested.  (See FAQ # 9) Test everything where it lives.

What tools will I need if I want to try this repair myself? - You will need your owners manual, a wiring diagram of your entire car and a 12 volt, externally powered test light. After you address any concerns you may have found during the electrical test, you then obtain a external powered (ice pick looking) test light with lead and clip to test each and every fuse in one to three fuse panels. Get out your owners manual, find out what circuits ( it can be 2-4 different circuits) each fuse protects. You will then need to start and run the engine, turn on all the lights and accessories, then test both ends of all fuses to verify that each end has 12 plus volts and power is traveling through the fuse.

Any fuse that does not light up on one side will probably be bad, find another fuse that is the same color, length or amperage and switch it with the bad one.

If both ends of the fuse are dead, identify the fuse and what it protects and make sure you have that particular accessory turned on. It may be that you have a bad ignition switch and it is not powering up the ignition portion of the fuse block.

Fuse blocks - Most fuse panels have two sides, one side has power all the time and that side runs things that work without the ignition key turned on. Things like the brake lights, the hazards, the courtesy lights, the dash lights and cigarette lighter. So fuses that will light your test light without the key being turned on are on this side of the panel. This is the battery portion of the fuse block. If it is not powered up, you most likely have a bad or burnt fuse link at the starter, at the starter solenoid, at the alternator or at the battery terminal area.

The other side, the portion of the fuse panel that has fuses that protect those circuits that need the ignition key turned on, are accessories like wiper, a/c and heater blower, turn signals and radio. This is the ignition portion of the fuse block.

Headlights - Most domestic headlights are protected by an internal circuit breaker in the headlight switch. Many import cars have fuses that protect the headlight circuits, the owners manual will show and tell you what your car has, a circuit breaker or fuses protecting the headlight circuit. Last, if you have one headlight out, the easiest way to see what it is, is to switch the bulb with a known good one first. That will tell you if you have a power or ground problem, or a burnt or bad bulb.

I found a blown fuse, now what? - This is where I'm going to lose most of you. Each fuse usually protects 1-3 different items. You must "unload" each of the items on the fuse first. So if the radio, cigarette lighter and courtesy lights are all on that blown fuse, one way to track the short down is to disconnect the radio, the cigarette lighter(s) and all of the courtesy lights. Then plug them back in one at a time. Inspect each socket, plug and bulb. Look for melted plugs, wires touching and broken filaments.

EXAMPLE #1 - I remember a Cadillac where every time you opened the door, the radio station would change. We found a blown courtesy light fuse, we tracked it down to a shorted cigarette lighter in the back seat (one of the grand kids had dropped a penny in the socket) and once we pulled the penny and replaced the fuse, the problem went away. How did this happen? When the door was opened, the courtesy light were triggered on, but they had no power because the fuse was blown. That bad circuit would try and run using the radio circuit and when the power load was spiked to the radio causing the voltage to drop, the radio would change stations. Or at least that is the best guess we could make.

But I want it fixed right now - Sometimes, when you have an intermittent electrical problem, it is best to take a wait and see attitude. All electrical problems will cost tens or hundreds of dollars to find and 95% of those will cost one dollar to fix, i.e. move the wire, replace the shorted bulb, tape up a bare spot, fix two touching wires in a harness plug, etc.

What are the most common areas of concern? - That one is easy. Something inside the cigarette lighter shorting it out, bad trailer plug at the rear bumper or newly installed towing plug shorted to ground, newly installed stereo, amplifier or radar detector, bad alternator (just unplug it) or wires that have fallen out of a harness holder and fallen onto the hot exhaust are very common things we see day in . . . day out.


Subj: Car Repair FAQ 55 
Date: 5/28/2003 10:57:26 PM US Mountain Standard Time
From: kdstaller@earthlink.net
To: mark@marksalem.com
Sent from the Internet (Details)


Excellent website, especially the FAQ section.

On #55, weird electrical problems, there is another common problem to strange automotive electrical anomalies.

My wife had her transmission replaced under warranty by the dealership that sold her the car. Two days after it was returned to us, the dash board lights would start randomly blinking on and off, warning buzzers would chime in, and the automatic seat belts would retract and deploy while driving down the road. When taken back to the dealership, they discovered that they forgot to re-attach one of the ground straps in the engine compartment.

I discovered a similar problem with my 1989 Mercury Cougar. Two of my batteries failed due to a broken ground post. This resulted in an erratic reading of the oil pressure and temperature gauges on the digital dash display until the engine warmed up.

As more of the display and control systems on modern cars use digital electronic sensors and display circuitry, they will be more susceptible to intermittent ground connections. Check for loose, disconnected or corroded ground straps and connectors. If your battery cables are tightly routed to the battery (no slack in the cable), inspect the ground terminal post for movement.

Kris Staller
Electronic Failure Analysis Engineer
( ITT Automotive/Industries 1988-2000)


Thank Kris, you bring up a fine point....Mark

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