1973 - 1979 F-100 & Larger F-Series TrucksDiscuss the Dentsides Ford Truck
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hey guys, my lights flicker at an idle, i have checked the voltage rgulator under the hood, thebattery and the alternator and all are good. an old timer told me that i had a voltage regulator behind the dash, but its not in the chiltons and i cant find it. any advise???
C'mon man, ya gots to be a little more specific so we can help you out..... Do you mean the headlights or the dash (instrument) lights? By discussing the VR, then I presume you're talking about the dash lights.
yes the dome light flickers inside the cab when it is on andthe truck is at an idle, also the headlights when the truck is at an idle. I have checked every ground i can find. It really all leans toward the VR under the hood. its gotta be something real simple, driving me NUTS! Thanxs for all the input i really appreciate it!
Is there anything causing a drain on the battery? Something aftermarket like an amplifier can cause this, especially in these older trucks as the alternator doesnt begin to fully charge until around 1200+ rpms.
Gotta agree with pretty much everything that has been posted so far. The alternators on these trucks are not extremely high powered, you're talking around 61 amps tops. Any alternator at idle puts out well less than it's rated maximum.
Just as an example, Powermaster lists their 140 alternator only puts out 80 amps at idle. That's only 57% of rated output. Their 200 amp unit only puts out 120 at idle, 60%.
So if you wanna be on the optimistic side and say your alternator puts out 60 amps at full speed, then it puts out 60% of this at idle, you're talking only 36 amps. A typical headlight is around 60 watts at 12.8 volts. That's 9.3 amps for the pair. Even if you're not powering anything else but the ignition system you've only got 25 amps worth of capacity. Couple that with a questionable ground here and there and a little bit of corrosion on a few connections, a marginal battery, then suddenly you've got a whole slew of electrical problems even though your alternator and voltage regulator may be just fine.
Anywho, you're wasting your time chasing that mysterious behind the dash voltage regulator. It deals only with your instruments and will have no impact on your headlights, dome light, etc. You need to disconnect and clean every contact on your alternator and make sure that all of your connections there are solid. You need to do the same thing with your voltage regulator and make sure that it has a very solid ground. Use a meter and measure the resistance from the voltage regulator's mounting point over to your negative battery post. If that resistance is anything more than around 0 you need to re-work it. Make sure your negative battery cable is clean, free of corrosion, and tight and goes directly to your engine block. Then you need to make sure that there is a solid ground from the block to the frame and also to the chassis. The positive cable needs to also be free of corrosion and clean. Just because it "looks" clean doesn't necessarily mean that it is. Take everything apart hit it with contact cleaner and a wire brush, steel wool, sandpaper, SOMETHING to clean them up. And finally make sure your battery is fully charged so it can kinda act as a buffer for when your alternator falls short.
An alternator really is a lousy battery charger and if your charging system is anything less than perfect it will not keep your battery fully charged. Put a smart charger on your battery and let it bring it up to full charge slowly. You will probably be surprised at how low it thinks your battery really is.
Make sure your negative battery cable is clean, free of corrosion, and tight and goes directly to your engine block.
The Factory wiring on the 300-6 the negative battery cable goes from the battery Negative terminal, and goes directly to the starter mounting bolt where it bolts to the engine. If the starter mounting surface to the engine is not really clean or good, this can cause a poor ground to the engine.
Also midpoint on this cable there is a tab that attaches the cable to the frame. This is how the frame is grounded from the factory.
Make sure these are clean and tight, and present, as replacement cables do not have the tab on the cables to ground the frame, so you will have to improvise something.
Hmm, didn't know that about the straight 6. The cable on my 302 goes straight to the block kinda behind and below the alternator. I guess if it were me trying to replace the cable I would go for a nice solid cable right from the battery cable to the starter bolt and then use a second cable to come back to the frame.
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