ELECTRICAL PROBLEM ???

[Quick Pony]

Hi everybody and Merry Christmas. I am having some problems with my 1991 Ford LX 5.0 Convertible. A few days ago I went to start the car and nothing happened when I turned the ignition. No clicking sounds, etc. I charged the battery and went to Autozone because I had bought the top of the line Duralast Battery there about 4 months ago. The guy came out with his machine and said it has a bad starter! Another employee came out and had me rev up to 2000 RPM and said its the battery. They gave me a new battery but the car was still not right. My factory guage needle was in the middle instead of showing a charging status. As I turned on more accessories, (lights, radio, power windows) the needle showed discharging.
Also, ever since this problem started, my airbag light flashes slowly all the time no matter what gear I'm in. Car is an automatic. Also everytime I go to start the car, it pauses and then it starts. Yesterday I went to start and nothing. I replaced the battery clamps. Belt is nice and tight. Alternator is about 3 years old. I charged the battery up fully. Car started after a short pause. Airbag light still flashing. Guage shows discharging while driving!

Any ideas? I'm not working right now and money is tight. I can't afford both a new starter and alternator.

Also when I replaced the negative terminal I noticed that I have a large black wire and a little black wire going to the negative post. What is the little wire for?

Any help would be greatly appreciated. Hope everybody had a great holiday.

Thanks
Larry

 

[grrrrrrr]

Sounds like you got a bad alternator?

 

[jrichker]

The middle mark on the dash voltmeter is 14 volts. It takes 13.2 volts to charge the battery. If you can maintain the needle at the middle mark when you get above idle with an automatic, you are doing OK.

The small black wire on the negitive battery cable is chassis ground for the battery. It must have a clean shiny spot to connect to for the electrical system to function properly.

Grounds are important to any electrical system, and especially to computers.

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery.

4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt for help troubleshooting voltage drops across grounds

 

[mirage86]

I had a similar experience. After replacing the battery, alternator, and voltage regulator it turned out to be a loose wire. One of the push on wires on the back of the alternator had come off and I never saw it till after everything was replaced.