Electrical question

[Mike M.]

Have a 64 with 300 hp....and very little electrical knowledge. My battery is fully charged, yet when I switch the turn signal on or pull the headligts on, my ammeter moves to the negative until turned off. For the turn signal, the ammeter needle moves back & forth in time with the signal light going on and off. Probably something simple I hope?.....thanks

[William C.]

Re: Electrical question

Where is the needle with everything off? Is it dead center, or skewed to one side or the other? Remember the meter is really reading voltage drop across a wire in the engine compartment.

[Mike M.]

Re: Electrical question

I believe it's dead center, although may be very slightly leaning towards negative side. Can't view the car right now. Would you mind explaining the possibilities for either situation? thanks

[Stephen L.]

Re: Electrical question

What you are observing is normal/correct. Ammeters measure the current draw on the battery as items turn on off and the regulator compensates for the loads. As long as the meter is at or near positive side of center with the rpms above 1200 then everything is Ok. If it stays more negative than with the key off, with things turned on and 1200 rpms then you probably have a problem.

Newer cars have voltmeters which measure battery voltage, which is slower to react to a load (as in the lights were left on and the battery slowly discharged without the engine running) and the voltage slowly drops off.....

When the ignition switch and lights, accessories etc are off the ammeter is showing no current. If the needle is slightly off center its just a mechanical situation of how accurately the needle was installed on the shaft.

[Mike M.]

Re: Electrical question

It does happen while I'm driving and above 1200 rpm.......thanks

[William C.]

Re: Electrical question

Then I would have a good shop check the alternator output and also the voltage regulator

[Stephen L.]

Re: Electrical question

When I refered to 1200 rpm I meant that the indicator would be at near/above zero. You'll see a needle deflection when you first turn on the lights and as the signals cycle but the meter should return to the above indication during a steady state condition no matter the rpm. This is typical delay reaction of the mechanical voltage regulator. This is normal.

[Mike M.]

Re: Electrical question

Thanks for your help!

[Mike M.]

Re: Electrical question

Got it. With the key off and the headlights on, the needle stays in the negative and doesn't return to center.....