AMP meter reading negative recently....

[landmizzle]

Hi all,

I don't know if I'm observing something that is normal or not ( I don't think so but,......). With Summer here and long daylight hours, I haven't driven at night lately so maybe I'm just being paranoid but, on my last trip I've noticed that with the headlights on, my AMP meter is reading about an 1/8 of the way into the negative side of the gauge. This caught my attention as being odd. Driving during the daytime with lights off course, the needle is stable down the middle. I've also noticed that when the ventalation fan is on now, the neeedle moves slightly into the negative side of the gauge.

I've replaced the battery, and the voltage regulator with no changes. I've spoken with my mechanic an he had me disconnect the Voltage Reg. plug and jumper the middle pins ( white wire, white/black strip wire) on the engine side of the harness. He stated that this should get the alternator to deliver a full charge and the AMP gauge should read full positve to the right of the gauage. If this occured the Voltage Reg. is bad. If not, the the alternator is bad. There was no change when I did this; needle read 1/8 of scale into the negative as before.

Does this sound like the proper diagnosis? I really don't want to get buried in the "blindly replace" game. It makes sense to me but, electrical issues are not my strong point. All suggestions welcome!

Best Regards,

Landmissle '72 240Z

[240ZMan]

You didn't say this, but I will assume that this has been going on for some time and that you can still start and drive your Z without the battery going dead. This would suggest that your alternator is able to supply just enough current to run things during the day, but can't keep up when any additional load, such as lights or fan, are added.

Given you have already replaced the VR and battery, I'd suggest you take the alternator to a local parts store such as Autozone where they can bench test it. They will be able to tell precisely how much current it can put out. Assuming it's only a few amps, you know the problem. If it passes with 50 or more amps, I'd be looking at the wiring around the alternator and VR to see if there is a problem between the two.

Another thing to check if you didn't when you changed the battery is the condition of the connections to the battery. Excessive corrosion/oxidation can cause the VR to improperly read the voltage of the battery. Look for broken, rusted, cracked wires around there as well.

Good luck.

[beandip]

Right on the money, one thing to add is to check the ground wire and as 240zman stated the connections at BOTH ends. This is vary basic but did you check for a loose fan belt ? This will cause the problem you are having to.

[landmizzle]

Wanted to thank you two for taking the time to reply to my post. I really appreciate it.

The good news is that the diagnosis was correct; it was the alternator. The bad news is that the old alternator wasn't supplying as much current as I thought and gave it's final death rattle on me today. Consequently stranding me about three miles from work today. Fortunately, one of my co-workers gave me a ride home (about 50 miles.) so that I could recharge the battery and as luck would have it, the new alternator I ordered arrived once I got home.Yea!

60 minutes in the 100 degree sun and the alternator along with the recharged battery were installed. She's running like a champ again.

Best Regards,

Landmissle '72 240Z