Battery or alternator???

Strange thing happened. My rpms are usually up around 900 and steady once the car warms up. I never drive it at night but tonight i did at dusk. Had the lights on. Stopped at a couple stop lights and oficed the idle seemed low like around 6 or 700. The car was warm. Got home put in garage and let it idle and was still doing it. Turned off lights and the rpms jumped back up to about normal. Turned on the lights and they dropped. Coil is brand new. Does this sound like an alternator or battery issue? I am not overly concerned yet just more curious what why the lights would put that much load on this motor to where the rpms would drop like that...Pardon my typing i am on an iphone!

Can you tell us what you have for a generator or alternator?

Also, what are your headlights? Stock sealed-beams or H-4 conversions?

tnx.

gn

I will have to do some digging to find out...

its the 3 wire set up.

ie. the headlights. If you have small replaceable bulb in the back center of the headlight reflector then you have H4 lights. If there is just a plug with 3 wires then you have a normal sealed beam headlight.
The problem could be one of several things. The alternator isn't putting out enough voltage to compensate for the voltage drain of having your headlights on, the battery is bad or wiring is all wrong. If the wiring to the headlights isn't of sufficient size then that could cause your problems or, if coil voltage is taken from the headlight circuit that too could cause your problems. Faulty grounds are another source of similar conditions. You might start by checking the ground circuit on the headlights. Additionally, if the primary wire that carries 12 volts to the fuse box that feeds other circuits isn't at least 10 gauge then that could contribute to your problems

Todd.... First things first.... Check the connections at the battery posts, cable ground, and cable to starter ..... Corrosion at any of these points will cause these symptoms....

These are not the only possible causes, just the more common I've encountered....

That ground circuit Larry and Leon mentioned might be nothing more than a smallish-looking wire that appears to go nowhere except to a bolt. In your case, living close to salt water, I think that'd be the first thing I'd look at.

My wires are now bundled, with the headlight ground going to the metal frame of the car instead of terminating at the bolt to the headlight bucket. My car was originally put together by a retired doctor. Pretty smart guy.

When you put more electrical load on the alternator, it takes more force to spin and increases the load on the engine. It's just easier to notice because the engine is making very little power at idle. Bigger engines produce more power even at idle so you don't notice the drop as much and of course modern engines have idle air control so you don't notice it at all.

The others have covered the reasons your lights might have a higher load than usual.

Throw a voltage regulator on it, because my money is on the alternator.

Here's why...

When you have the headlamps on (and the alternator charge is inadequate), then your electricity tries to share - like spilled water tries to all find the same level. Neither the headlamps NOR the ignition system have adequate electricity, so it runs like poo. Not enough juice to adequately feed the ignition system.

Turn the lights off and the alternator's diminished capacity is adequate to run the ignition and the RPM picks up. You are probably actually running off just the battery already.

By the way, if you are ever forced to get yourself home with a dead alternator, always shut off every electrical item you can (stereo, lights, blower fans, etc). If you are just running an ignition system, you can go for hours on a fully charged battery. Less if your fuel pump is electric.

angela

Todd,

Like Red Green says, if women don't find you handsome, they should find you handy. If you're not, consider a local auto electric shop. An experienced guy or gal can diagnose your problem, fix what's wrong, and have you underway in short order.