voltage dropping

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Mar 23, 2010 | 09:57 PM

mobyrobe

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voltage dropping

Hi I'm new to the forum. I have a 1973 f100 302. Brand new alternator and regulator (didn't fix the problem). With the engine running I am only showing around 12.3v. When I turn on the headlights, it drops to 11.8 initially and then slowly drops from there to around 10v in 5 minutes. My headlights are pretty dim and my brights won't switch on. Without the headlights on it runs great but when they're on, my battery eventually dies. I would greatly appreciate any advice/suggestions before I start tearing into my wiring!

Mar 23, 2010 | 10:59 PM

Bullitt390

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Check your fusible link coming off of the + post on the starter solenoid.

Josh

Mar 24, 2010 | 01:14 AM

BlackLabel78

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I was just having these same issues with my truck. Did you have your battery checked? I did the same thing and replaced several items before figuring out that my battery would not accept a charge. Get that checked if you have not already.

Mar 25, 2010 | 10:49 PM

longroad1921

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i had same problem...my battery was good though...you might also want to check your ground wire(s)...from battery to engine and also to body of truck...if you haven't already.....

Mar 25, 2010 | 10:57 PM

mobyrobe

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I installed a brand new battery last night...no fix. I did notice that the STA wire coming off of the alternator is not hooked to anything. Also, there is a box located in between the battery and solenoid that I'm not sure what it is. It is about an inch square or so and has a 3-blade connector that has yellow wires plugged into it. Brand looks like "Littelfuse" but I have not had any luck finding anything like it online. Any idea what this is?

Mar 25, 2010 | 11:45 PM

hasteranger

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From: West Virginia

I think you have narrowed down your problem: with headlights off, it runs great, but with headlights on, it drains the electrical system. Assuming you have tried simulating the drain of the headlights by leaving them off and turning on the radio, blower motor on high, and windshield wipers on high, and had it still run, ok, well: That means you when your headlight switch is turned on, something AFTER the switch must be draining the system. A bad ground wouldn't do this. Most likely a short, especially since you said your high beams won't come on. I'd check your hi/lo beam switch, your headlight switch, and your headlight wiring.

Chasing electrical gremlins isn't fun but a good multimeter will save you a lot of time.