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Old 04-10-2005, 02:02 AM
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Headlights get brighter when i accelerate.

Hello. not a BIG problem, just something that is bugging me. i have a 67 mustang with a straight-6, and at night when i start my car and turn on the lights, as a rev my engine a little, i notice that my lights get brighter. and then with the rpm comes down, the lights get dimmer. what does this mean? it's not like its that Extreme to where i notice it when i'm driving or anything, its just kinda wierd i think.
thanks alot

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Old 04-10-2005, 02:34 AM
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You either have a low amperage alternator or a weak battery.

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Old 04-10-2005, 03:03 AM
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Doc here,

Put a DMM (Digital Multimeter) on positive and negative of your battery and measure the voltage..If it reads in the mid to low 11's,or under...Try a battery charge (6 to 8 hours at 10 amps) Then measure again. Does it Come up to 12.75? If not you probably have a bad cell.

If that test is good, 11.9 to 12.75 static..(or better) then start the engine, run it at about 1500 rpm's and monitor the meter...should read 14.4 volts...then idle down, It should read 14.4. Turn the lights and watch to see if you have a drop..If so...a few things to try,

Clean and tighten all your battery cables. Check your ground connections around the engine compartment make sure they are tight and clean. Is the alternator bracket Aluminum? Is it corroded? If so, clean it, and run 8 or 10 gauge wire from the alternator body to a good engine ground. You have electrolysis From the dissimilar metals, not making good contact. (I don't remember on that car anymore, but) If you have an external Mechanical Regulator, you might try to adjust it so it cuts in at a higher voltage than it is now.

IF ALL ABOVE DOES NOT WORK (and for future problem avoidance) Try this:

Locate The main (Heavy battery cable) ground in the engine compartment, should be at or near the starter. Get a Battery Cable with ring terminals on each ends, and run that from the main ground wire to the Frame and bolt it up. From that same main ground, run 2~ 8 or 10 gauge wires, ground one at the firewall, the other at the Alternator Mount.(So you know ground is good and continual throughout the car.) The extra Grounding won't hurt a thing, and may possibly head off future problems.

If It still does it, Then you alternator / Regulator is beginning to fail...time is now to plan replacement!

Hope it helps!

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Old 04-10-2005, 11:43 AM
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thanks alot for the quick replies. ill try that
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