1966 F100 4.9
My ALT guage barely makes a move to the neg when the key is turned on. When the truck is started it sits at what I can only guess is 15, based on the 0, 30, and 60 indicator lines (not exactly precise instrumentation). When running and I turn the lights on it goes to 30. Ive seen it as high as 60 before. I know there must be wiring issues because this truck has been carved up and jimmied to death. I just need to know where to start.

 

I'd start with your voltage regulator, although it doesn't necessarily explain your negative key-on problems. $27.99 at your local Autozone.

Voltage Regulator | 1966 Ford F100 1/2 ton P/U 2WD 6 Cylinders 4.9L 1BL | AutoZone.com

 

Are you actually having problems with it charging your battery and not starting or did you just notice the dash indicator not moving much? I would get a digital volt ohm meter (dvom). Harbor Freight has them for as low as 4.99, free if you have a coupon. If the alternator is putting out 12-16 volts and charging the battery, don’t worry about it. I would not just put a regulator on because I saw a low reading on (not exactly precise instrumentation).<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
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The AMP meter only moves if the battery is being charged or being discharged.

It does not indcate ALT output.

It should not go up, meaning a higher reading, when you turn on the lights with the engine running.... unless you have added relays to power the head lights directly from the battery.
Just dont worry about it if everything is working OK.

 

+1. You're going to need a voltmeter anyway, go ahead and pick one up. Then check the voltage across the battery terminals with the truck running.

 

Thanks all. Im not having charging problems but I do have electrical gremlins. When I use the high beams I can count the seconds until all the lights turn off. Not ideal on the back roads at night. I replaced the headlight switch some time ago and I thought that solved the problem but apparently not. I dont know if they come back on by my frantic jiggling of the headlight know or if on their own. I did replace the voltage regulator, if for no other reason that its a cheap upgrade. I dont know about whether a relay was added but I do **** the wiring is both very old and very jimmy rigged. Ive been avoiding a volt meter because Im electrically inept, but it appears its time to learn it.
So, if there are no relays added and the amp meter goes up when the lights come on, what would that mean? Like I said, sometimes it goes up to +30 and sometimes +60.

 

no worries- we'll walk you through whatever we can. and if we get in over our heads, "franklin" down in the electrical forum can take over.

as for the headlights- this is a well known issue, and there's a fix which is an improvement over the stock wiring. the stock circuit is not ideal, and after 40 years or so, corrosion in any number of places (headlight switch, floor dimmer switch, the wire itself, etc) will cause the circuit breaker to cut in and out.
Whiter Whites, Brighter Brights .: Articles

i can't really say about the amp gauge, but...i saw one once wired up *backwards*. if i remember correctly, that made the gauge go up when the battery was being discharged. pretty funny.

you're going to get good with the voltmeter. its a good thing.

 

Rust is too a color,

If when you replaced the headlight switch, it was new and or a good one [sometimes, new ones are bad out of the box], then it might be a good idea to also replace the floor mounted dimmer switch. It is not expensive and is easier to replace than the headlight switch. The dimmer switch is exposed to moisture and dirt, due to its location and can get corrosion at the terminals, which will pull additional amperage and can trip the headlight switch's internal relay. It was designed as a safety feature to prevent fires while blinking on and off to allow you to get to the side of the road in the darkness.

 

Thanks 1986. I'll try it. Btw, it was a new switch.