Hello all,
I have a 1980 f-150 and I am having trouble with the battery discharging/starting/lights and radio dying on me in the middle of a drive. I bought it used. Changed the starter first because it would start hard. Worked all summer. Now It won't keep a charge. The battery has been tested as good 2 days ago, and I just replaced the alternator. It works great on a full charge, but about 15 minutes into a drive, my interior lights quit working, radio quits working, and my headlights are dim. Could this be a voltage regulator? I am 99% sure I hooked the new alt. up same as the old one. After i replaced the alternator i thought i was golden. Drove it to work NO problems...even 15 minutes in. Come out for lunch, DEAD! Charged it for 1.5 hours, and got home no problems again. Maintenance guy at work says voltage regulator. Is this a possibility? Any help is appreciated. Sorry for the long thread but i wanted to give all the info I had. Thanks.

 

What does the voltmeter say while the engine is running. It should hover around 14 volts.

Since you replaced the alternator, we can safely rule out that component. I would lean toward the regulator being the problem. Are all the connections and wires in good condition? If there is no voltage to 'excite' the alternator, it won't produce any power itself.

 

These trucks don't have a voltmeter in the dash, but you are right, the first thing to do is get a voltmeter/tester and put it on the battery with the engine running. It should be around 13.5-14.5v. If it's 12v or less, it's not charging.

 

No, I mean hook up a voltmeter to the battery and looking at the voltage.

The ammeter in the cab doesnt show too much detail other than if its charging or discharging and if by a little or a lot.

 

I have an update. I put a new exide battery in it right off the shelf. Also got a new voltage regulator. Hooked it all up. Started right up. Turned everything on (lights, dome light, heater blower motor, radio) and It reads 12.03V. Let it run for a bit, it jumped up to 12.09V. Let the engine run for 5-10 minutes and watched the meter closely. With everything on and the engine running (at different RPM's because i put a small weight on the gas) the voltage never dropped below 12.09V. What do we think? The old voltage regulator had one prong out of the 4 coroded/burnt or something. Anyways, it wasn't bright silver like the other 3. I am worried my volts are low, but it seemed to stay above 12V with everything running and my RPM's weren't too high. Thanks for everyone's input.

 

You did not read the previous post. You are not charging. It will die in a few days if you keep running it. You need to do some more tests.

 

Well I am out of ideas. New starter, alternator, battery, voltage regulator. Connections look good. Fuseable link looks good. I am so frustrated.

 

Well you've replaced most, if not all, of the major charging system components. Let's go back to basics here..

How about the wiring? Does anything look bad, burnt, or corroded? How about good grounding? The original grounding cable, at least on my '85 F150 (302), went from the battery (-) to an engine bolt right behind the alternator. In the middle was a metal clamp which bolted onto the frame. I replaced this cable with 2 cable. Engine to frame. Frame to Battery (-).

Now for the wiring from the voltage regulator to the alternator. Just do some basic continuity checks on the each wire running to the alternator.



This is the wiring diagram for the 1G alternator setup. If you have an external voltage regulator...this is what you refer to.

 

This might help ya:

https://www.ford-trucks.com/forums/1...t-need-it.html

 

Don't rely on a fusible link "looking good". I had a charging problem with a friends old chrysler. Ultimately, the "new" battery was bad, but it did have a burned fusible link. Outer insulation looked good, but the wire was gone inside!

 

You can check the fusible link going to the alternator by checking for battery voltage on the large output lug on the alternator with the engine off. If you have 12v there with the engine off, it's good.

 

I do believe I may have officially f'd up. Checking connections and tracing wires today. Unhooked alt. And when I hooked it back up I accidentally put the field wire on the negative post on the alt, the stator wire on the field terminal. Got real Smokey and sparky real quick. I pulled the neg. Battery cable as fast as I could but not until a nice fireworks display. What could I have damaged? Everything?

 

jEGS SELLS A ONE WIRE ALTERNATOR that will eliminate a lot of wiring and the regulator, plus its 100amp I believe. Hard to tell what you let the smoke out of.

 

If you ground the field wire from the regulator, it usually burns the regulator out.

Do this test; Hook a scrap piece of wire to the field terminal of the alternator that will reach the + of the battery.

Make sure you do the test above, and be sure the fusible link to the alternator is good.

If all that checks out, start the truck, put a meter on the battery to watch the voltage, and then stick the field terminal wire to the battery +. If the alternator is good, the voltage on the battery should jump way up, and you might hear it whine a little bit. This puts the alternator to wide open charge, and will verify it's good.

 

just the field lug? What abt. The battery terminal on the back of the alternator?