electrical nightmare

[JimmyRGT]

OK so driving home from work a few days, the voltage suddenly drops very low, the battery light comes on, and the car barely makes it home. Of course it will not restart and the battery is completely drained.

I get the alternator checked and it is bad, same with the battery so I replace them both, get everything hooked and the car starts immediately. However the voltage is still way lower than it should be. I take it for a test drive and the voltage slowly drops while I am driving until it gets to the dangerous range again and the car shuts off. It wont restart without being jumped again.

New alt and battery test out fine. It seems like something is severly draining my electrical system while the car is running, any ideas of what it could be? Any suggestions would be appreciated.

95 Mustang GT and yes i have U/D pulleys but have never had a problem with them.

 

[Car Nut]

You've probably got ground problems.

Disconnect the ground cable that goes to the engine block (under the waterpump on driver side). Clean the bolt, nut, and wire end with light sandpaper to a shiny finish.

I went a step further and added a seperate negative battery cable from the negative battery post connection to the front of the car beside the radiator support. I unscrewed on of the grounds and added this cable to it.

Lastly, and probably most importantly, get a brand new 2 or 4 guage negative battery cable and replace the block to frame ground cable. The stock one is thin and looks kind of mesh like. You only need about a 14" of cable.

It is quite unreal how poor our cars are grounded.

I had the same issues you described (bad alternator/battery) and had the same problem not being able to start the car. Once I cleaned up the first ground I mentioned, the car started up perfectly until the next time I washed the underhood area. Now that all grounds are clean and/or upgraded, I never have issues. Alternator and battery issues are very easy to detect now as well.

Good luck and let us know what happens.

 

[Black95GTS]

You've probably got ground problems.

Disconnect the ground cable that goes to the engine block (under the waterpump on driver side). Clean the bolt, nut, and wire end with light sandpaper to a shiny finish.

I went a step further and added a seperate negative battery cable from the negative battery post connection to the front of the car beside the radiator support. I unscrewed on of the grounds and added this cable to it.

Lastly, and probably most importantly, get a brand new 2 or 4 guage negative battery cable and replace the block to frame ground cable. The stock one is thin and looks kind of mesh like. You only need about a 14" of cable.

It is quite unreal how poor our cars are grounded.

I had the same issues you described (bad alternator/battery) and had the same problem not being able to start the car. Once I cleaned up the first ground I mentioned, the car started up perfectly until the next time I washed the underhood area. Now that all grounds are clean and/or upgraded, I never have issues. Alternator and battery issues are very easy to detect now as well.

Good luck and let us know what happens.

This is great advice. I'm an electrical engineer and I couldn't agree more about how poorly our cars are grounded. I also added a second ground from the battery post. U/D pullies are very rarely an issue unless you have some big amps.

The fuel pump ground is also lacking IMO.

Adam

 

[HISSIN50]

Check the alternator fuse in the underhood fusebox, and the fusible links on the charge cable (they're on the cable between the PDC stud and the PS pump). If either has an issue, you will run off the battery.


At your alternator's regulator, the A terminal should read within 200 mA of battery voltage.
The I terminal will float voltage.
Ensure the stator loop is intact.

You can turn your alternator into a 2 wire (charge and excite circuit) if you need to (for diagnostics or permanently).

Good luck.

 

[gcomfx.com]

I concur on checking the ground wires. I had issues with my battery corroding and the car not wanting to start. The ground from my engine block to the rail/firewall area was bad. The bolt had rusted severely. When I put a larger alt. on the car, I had to increase the alt cable as well. I used the old cable to make two new engine grounds. Put one on each side. Hooked to the frame and the engine mounts. Works great now.