f-150 ford p/u (4.6) battery discharges fast while running.

[x1957x]

I have a problem with the charging system I think. What happens is truck died the other night and I noticed that all the post clamps were loose via some cleaner I put on and forgot to tighten them after.. Anyhow I took it home and charged the battery and put it back in and tightened every thing up and did not drive for a couple days. Yesterday I got in it and fired that old girl up and it said it was charging on the silly-me gauge(over half way up). I started to drive it and about a half hour later driving down the highway I see the gauge is going back to the discharge thing again. Got it home before I lose power(barely)and put the battery on the bench and on charger and it says it is at 10% of charge in it. Battery or charging issue? Thanks 57

[Jeremy airjer W]

With the truck running check voltage at the battery. If you see around or more than 14 volts than the alternator is working. If the voltage is less than 12.5 volts the alternator is not working.

[x1957x]

Finally got to it and I put in a new alternator cause it was at 10.4 volts. I put in a new one and it is running at 12.1 amps. I do know that it has a voltage regulator built in so with that in mind I changed the plug with a new one(3 wire) and the center wire goes to a small seperate plug that has the clip broke on it. I did not change that one. Put it all together and it is still running at 12.1 amps.Can it be the small wire? I did change the battery posts also. Still at 12.0 volts. Any thoughts on what else it can be? Thanks!!

[fishing tech]

Is the battery fully charged? The longer it runs or if you turn on the headlights does the voltage drop? Check and make sure you have power at the big red wire on the alternator.

[Jeremy airjer W]

You are not measuring amperage you are measuring voltage.

Are you measuring voltage at the battery? What's the voltage at the positive post on the back of the alternator?

Since you had an increase in voltage with the new alternator I would have to wonder if here is extra resistance in the positive cable. Or possible an issue with the ground cable/connections.

Checking voltage drops across these will tell you if there is a problem.

[x1957x]

Thanks Jeremy and fishingtech. I will check it today when I get home. Do you guys know what that middle wire on the 3 wire plug is for. It goes to a seperate little plug right beside it. When checking Volts not Amps(LOL) at the Alternator, do you use the neg. post on the battery for the ground or any ground on thhe motor or chasis? Jeremy, what do you mean an issue with the ground cable? I did change the connecters on the battery to. Extra resistance in the positive means what? What do I have to do if there is a different reading at the positive post at the alternator? Thanks bud!!

[Jeremy airjer W]

Extra resistance means a drop in voltage. If there is corrosion in the positive battery cable there will be a voltage drop.

Yes you will use the negative post of the battery for the ground. But you can also use the case of the alternator for ground.

When you replaced the cable ends you didn't by chance replace them will the black and red painted cable ends? If you did clean all the paint off them until you see the silver lead color. Put everything back together and your problem should be solved.

[x1957x]

Jeremy, hi.. I put a volt tester on it and 12.1 volts across battery. I went from battery ground to the hot post on the alternator and that IS also 12.1 volts. I did a ohms test and it stays at zero and beeps on the hot cable but when I do the ground from the battery to the fire wall or the selenoid I get anywhere from 4.1 to 7.6 ohms as it beeps. Huh. Dont really get it. Is it a bad ground cable to the starter or to the fire wall from the battery? Should I have got more of a volt reading on the hot wire? I know its not charging at all. Fuse? What next guys?? Whats the chance of getting 2 new alternators that were both bad. Could it be the small wire I talked about earlier on? Kinda lost at the things it can be!! Kinda eliminated all avenue's.. Thanks

[Scott K]

What year is it?

[x1957x]

It is a 1997 4wanderingeyes..

[Scott K]

This is a pretty simple system. Make sure with the key on, engine not running, that you have 12 volts on the big Yellow/white wire, make sure you have 12 volt power on the o/lb wire going into pin A on the regulator, also make sure you have close to 12 volts, more like 10 volts on the lg/r wire on the regulator with the key on. If you do,then you have a bad alternator.

[x1957x]

If I did this correctly I have 11.9 at the big red hot wire at the alternator and I have 12.1 at the yellow/white wire at the fuse link and at the alt. What color is the o/lb that goes into the A pin? I switched the 3 wire plug at the alternator and the new wire(biggest one) that was originally orange/black (from the fuse that was fed by the y/white wire is now y/white at the 3wire plug. The middle wire that feeds the little plug next to the 3 wireplug is still b/w and the 3rd wire is still green/blk. If I did this correct I have got reading's of 12.1, 12.1, and 11.9 at the (red/hot wire) on the alternator. Is the alternator bad then?

[Scott K]

I guess the easy way to put this is, with the truck running, and the connector plugged in, all wires, EXCEPT the single wire white and black wire should be about 12 volts, the white and black wire should be half of battery voltage. So about 6 volts. If you have 12 volts on the white with black, the alternator is bad.

[x1957x]

I do not have any voltage at the black/white wire off the 3 prong plug while the truck is running. The black and white wire goes to the little plug just beside the 3 prong plug. What is the purpose of the plug. Is it a stator plug? What next?

[x1957x]

Hey thanks guys. I found the problem as it was, the green wire that goes into the plug had no volts but I checked the ohms earlier in the wire and it was good. But from the box to the Alternator there was nothing. Found a break in the wire where it had gone under the hose mount on the motor. Put on a heat shrink connecter and Bingo was his Namo!!! Thanks again guys!!

[delcecchi]

Good Job !!!!!!