Car surges when lights are on!

Hi Guys,

My car idle surges when I turn on the headlights.  Do you think I should just replace the alternator or should I check something else first?

I'd do some checking with a volt meter first. See if the battery is up to snuff, check with no load, then with lights on. The check it running. Possible alternator problem, but do some diagnostic work and confirm it befor you replace it. Are you running any kind of after market ignition? Like a cd box?

Thanks Pumps,

I think the battery is in good shape (looks fairly new, my inverter meter says 12.9v).  I'll use my multimeter on it tonight, but what numbers should I see when the engine is running?  The dash gauge shows it drop when the lights are on, but frankly I didn't believe it seeing that the gauges are pretty inaccurate in general on this beast. 

The dash gauge should drop some when you turn the lights on, anyway, because the lights are taking more 'lectricity to run them. It should come back up, tho, after a few minutes of above idle running.
With the engine running, you should have no less than 13.5 volts at the alt. and batt. Normal idle voltage is closer to 14.5. Anything lower than 12.5 with the engine running indicates a problem somewhere.
First, check the connections on the alt. itself. Are they tight, with no corrosion? Is the belt tight, and in good shape?. Check the batt. connections, pos. & neg. for corrosion. Make sure the ground cable from the batt. to the frame under the batt. box is nice, clean & tight.
These are some good items to check first, before condemning the alt.