I've been slowing repairing things on my 76 f150 and now a new problem occurred. The battery does not seem to be holding a charge and need some help trying to solve the issue. While driving the battery slowly drains and my lights dim and my truck will completely kill it self. I replaced the ignition switch and oddly enough doesn't seem to be doing it anymore but still testing that symptom. Here is what I have done so far.
1) I disconnected the negative batter post and tested with a test light to see if there is a short. The light did not light. Which I was told should be correct.
2) I have checked the fusible links and they are all solid.
3) I recently (two weeks ago) replaced the alternator and voltage regulator.
4) Checked the readings when the truck is off and get 12.45-12.57
5) Checked the readings at idle and get 12.3-12.4
6) Checked the readings at high rpm and get 12.3-12.4
7) checked the readings with fan on high and headlights on get 11.9-12.1
8) checked the readings after each test and the voltage goes back to the reading when the truck is off.

Is there any other test I could be doing to see if I have a wiring issue at all?
From my searching on the forums it sounds like my alternator isn't charging the battery. The old alternator was tested and reported fine but was old so i figured I replaced it anyways.

In recent weeks before this issue I replaced my cargo light, turn signals lights, and fuel selector valve. Those were the only wiring issues I perform.

 

Circumvent the whole thing and do a 3G swap you'll be glad you did.

 

Yes, I agree with him. Best upgrade

 

Not familiar with the 3G term/abbreviation/?

 

The OP's question wasn't "what upgrades can I do to my charging system," it was "why doesn't my charging system work." Telling him to forget about fixing the original system and go through an upgrade isn't helpful; not everyone wants to do that. Plus I don't agree that it makes sense to forget about the whole thing and just upgrade it all - there could be some sort of underlying grounding or drain issue that will make any charging system fail. We need to solve the original problem, understand the source, and then he's in a position to upgrade his truck, if he wants to.

Anyway...

To the OP: you observed that the voltage reading is not responding to RPM at all. This indicates one of two possibilities: (1) the alternator is simply not producing current, or (2) the alternator can output current, but the voltage regulator isn't responding to the load on the electrical system and the output of the alternator. Since the old alternator tested fine, have the regulator tested (most parts stores can do this). If that checks out fine, then we'll move on to the wiring and grounding.

 

Still don't know what 3G is.

 

Upgrading to a 3G does fix his problem. The original alternator is anemic at best and is poorly regulated. Doing the whole swap is cheaper than paying for a reman regulator or alternator.

A 3G alternator is a 3rd generation ford alternator. Do a search for the thread" just did - 3G swap" it will explain the whole thing. Super easy to do and you gain double the charging capacity or the original. I did my swap for $42.00 including a buss mega fuse holder.

 

Thank you.......

 

just jumping in on the thread, I have a 73 f250 camper special, what doner vehicles will the 3G come off of? how easy or complicated of an install

thanks

 

Here you go. I just learned it too.
https://www.ford-trucks.com/forums/9...g-upgrade.html

 

This isn't my point. Upgrading to a 3G might solve his problem. But we don't know what the problem is yet. If his voltage regulator is bad, which I suspect, then yes, a 3G alternator will solve the problem. But if his regulator isn't even getting power because of a wiring issue upstream, then a 3G alternator won't solve the problem because it will suffer the same issues as his current setup. This is why we need to at least help him understand why his current system is failing, and then he can decide how to fix it - whether that's an upgrade, or stock replacement.

He's not seeing the numbers he's seeing because the stock system is poor; he's seeing them because he has a problem. A stock setup should easily put out 14 volts when the RPMs jump. The stock setup works just fine until you start adding custom loads like heavy-duty electric fans, etc - none of which the OP has mentioned yet.

On a side note, I don't agree that a 3G swap is cheaper than a $15 replacement regulator.

 

Our trucks are notorious for bad grounding , you should be putting out 14 volts when running and 12 when not , my mechanic told me that the alternator was not grounded or the voltage regulator , so he told me to run a ground from the alternator to the regulator to the neg battery terminal and a ground from the engine block to the frame which I did , so far my alternator , voltage reg , starter and starter sulenoid have lasted over 3 years without problems , I used to replace the starter and alternator every 2 years , now I dont , give it a try and does sound like the voltage reg is not working , good luck .

 

Check for voltage at "S" term on regulator. Should be the red/green wire. Without this, it won't charge. This diagram may differ a litlle from what you have, but should help. If you have an idiot light instead of ammeter, the bulb being no good will not allow it to charge. Just a few more things to check.

 

@fmc400 Okay I will take the alternator and voltage regulator in today to be tested. I was thinking it had to do something with the regulator but wasn't quite sure since they were only three weeks old. I know though you shouldn't always trust new products.

@gfw1985 I checked the wiring and everything seems to be wired correctly. The corresponding colors are in the right location and did not see any crimps in the wiring. Edit: Also I have just the ammeter that doesn't seem to work but from the forums it sounds like these go bad anyways. Is that correct?

One thing I will check again is the grounding of the alternator, I cant recall checking that ground so I will make sure to do that as well. Eventually I may do a 3g conversion but like fmc400 said I want to try and solve my problem first before doing a conversion that may arise the same issue.

 

Just make sure you're getting the voltage on the red/green. No voltage/no charge.