The Ford Barn

Don-Ohio · 05-14-2010, 08:15 PM

This is a followup to a past post I had with the same problem.My headlights are blowing ( not both at the same time). I have installed a new alternator which during about a 30 minute drive and using a logging meter has an output of max.7.9 volts and min. of 5.6 volts.(measured on headlight wire). As suggested I ran a new ground wire to the lights from the frame and soldered them directly to the light socket. one light blew out during the drive. There is a small amount of discoloration in the bulb, so I don't think they're just vibrating and the filament breaking. Help !, bulbs aren't that expensive, but I've gone through 7 trying to find the problem. Thanks

MikeK · 05-14-2010, 08:41 PM

Your voltage should not swing that much with an alternator. Sounds like you have an engine to frame intermittent grounding problem, causing the alt. regulator to go a little nuts sometimes. Either tighten all the engine side-pan nuts, both on the oil pan and frame, or better, if it's not a judging points car (not with an alternator!

) add a cable from a tranny cover bolt to the same frame bolt hole the battery ground strap goes to. Remove and wire brush or scotchbrite both sides of the frame hole and all connections. Also re-check your battery terminals- clean and tight. Check all terminals from the alt. output lug back to the battery. Clean and tight? That should make the voltage reference steady for your alternator. The bolt holding the alternator to the bracket on the front timing cover is the alternator's ground. It's tight, too?

Mitch//pa · 05-14-2010, 08:52 PM

your alternator is putting out 7.9 volts which is causing your headlights to blow. the optimal high end charging rate should be 7.2. or even in the high sixes.

maybe tom can chime in on this he is our resident electrician

Bruce Adams · 05-14-2010, 09:25 PM

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A number of Model A owners run EIGHT volt batteries, and they do not complain about frequently blowing their headlamps. If 7.9 is the most the alternator is putting out, it would seem to be much the same as those with 8 volt batteries.
I wish I could offer more.

05-14-2010, 08:15 PM	#1
Don-Ohio Junior Member Join Date: May 2010 Posts: 7	headlights blowing This is a followup to a past post I had with the same problem.My headlights are blowing ( not both at the same time). I have installed a new alternator which during about a 30 minute drive and using a logging meter has an output of max.7.9 volts and min. of 5.6 volts.(measured on headlight wire). As suggested I ran a new ground wire to the lights from the frame and soldered them directly to the light socket. one light blew out during the drive. There is a small amount of discoloration in the bulb, so I don't think they're just vibrating and the filament breaking. Help !, bulbs aren't that expensive, but I've gone through 7 trying to find the problem. Thanks

05-14-2010, 08:41 PM	#2
MikeK Senior Member Join Date: May 2010 Location: Windy City Posts: 2,919	Re: headlights blowing Your voltage should not swing that much with an alternator. Sounds like you have an engine to frame intermittent grounding problem, causing the alt. regulator to go a little nuts sometimes. Either tighten all the engine side-pan nuts, both on the oil pan and frame, or better, if it's not a judging points car (not with an alternator! ) add a cable from a tranny cover bolt to the same frame bolt hole the battery ground strap goes to. Remove and wire brush or scotchbrite both sides of the frame hole and all connections. Also re-check your battery terminals- clean and tight. Check all terminals from the alt. output lug back to the battery. Clean and tight? That should make the voltage reference steady for your alternator. The bolt holding the alternator to the bracket on the front timing cover is the alternator's ground. It's tight, too? Last edited by MikeK; 05-14-2010 at 08:45 PM. Reason: Spelling! Duh.

05-14-2010, 08:52 PM	#3
Mitch//pa BANNED Join Date: May 2010 Location: Bucks County, PA Posts: 11,454	Re: headlights blowing your alternator is putting out 7.9 volts which is causing your headlights to blow. the optimal high end charging rate should be 7.2. or even in the high sixes. maybe tom can chime in on this he is our resident electrician Last edited by Mitch//pa; 05-14-2010 at 09:25 PM.

05-14-2010, 09:25 PM	#4
Bruce Adams Senior Member Join Date: May 2010 Location: Northport, NY Posts: 1,597	Re: headlights blowing Sponsored Links (Register now to hide all advertisements) A number of Model A owners run EIGHT volt batteries, and they do not complain about frequently blowing their headlamps. If 7.9 is the most the alternator is putting out, it would seem to be much the same as those with 8 volt batteries. I wish I could offer more.