Hey guys,

So I got a strange battery drain in my 96’ 7.3. At idle, my batteries stay fairly consistent, but when the truck revs up, it loses more and more voltage continuously.

I bought two brand new batteries and tried two new alternators to no avail.

Please help! Kinda my last hope before i list the truck for parts.

 

Sounds like a terminal/cable issue. Have you verified the alternators are actually charging? I've had numerous bad out of the box...lame remans.

The battery cables can corrode internally where you can't see also. Forst step would be checking for alternator output, if that's good then it's got to be an issue with the battery wiring

 

@Obspowerstroke7.3 , welcome to the FTE!

As Edgethis mentioned, I would lean toward an issue with the cables, terminals or main grounds being faulty. The Ford Service Manual states the following as possible causes regarding a condition you described.

• Circuity
• Voltage regulator
• Generator

If you have a multimeter and a few minutes, you can check the cables and connection points for resistance using the Ohm setting on the multimeter. There are guides out there that state what an acceptable reading is for a certain gauge wire of a certain length.

I hope this helps and keep us updated!

 

Discovered the alternator is not charging at all. Truck is straight up just running off the batteries. Alternator tested amazing at the parts store so i know the regulator is working. Wiring seems fine at the plugs…any thoughts?

 

It is said that an alternator is the most efficient shortly after a cold start and until it warms up. Perhaps when the test was conducted it was in fact working properly, but after the engine and components are up to operating temperature it fails intermittently.

 

Nope, this is how it is even after running a while.

 

If the alternator isn't charging it (or the regulator) is bad. Theres nothing else to point at.

The battery voltage should read 14.4 ish when truck is running. Give it a minute to account for glow plug draw.

I recently replaced a reman alternator twice that the store said was good and when I came back they were both bad.

 

Edgethis has already commented and said what the core of the issue is, but I will help break it down a bit for you.

Ford states the following are possible causes of your "strange battery drain" issue.

• Circuity (wires and connections)
• Voltage regulator (regulator)
• Generator (alternator)

If the truck is running solely on the batteries, that points to an alternator, regulator or wiring problem between the batteries and alternator.

Don't trust ANYTHING a parts store employee tells you. You can test the alternator for yourself with a simple and cheap multimeter.

Plugs? Do you mean lugs like on the batteries, alternator B+ post and the main grounds? If so, how do you know, were you able to test them for resistance using a multimeter? A visual inspection of a main wire/cable is only 33% of the inspection at best. The connections should be cleaned, the lugs should be cleaned, the conductivity and resistance should be checked. The wires could be corroding from the inside, again as Edgethis mentioned already.

I am not sure what you are trying to say with this statement. The truck is consistently running only on the batteries after a while? Is the battery light on in the dash cluster? Does your battery light work?

Following the guidance from Edgethis and Ford again, you have 3 areas to focus on, which he has said and I listed above.

Lastly, if you decide to sell the truck for parts due to an alternator issue, let me know first. If you decide you want to do a bit of troubleshooting, we are here to help and eager to help you. This is a fairly simple fix, you just need to investigate a bit in order to find the problem.

Keep us updated!

 

Check the connection at the two small plugs on the top of the alternator. Over time the connections get loose and cause charging issues. New pigtails are cheap and easy to replace.

 

One test you can pull for the alternator without a multimeter is to pull the negative terminal off the battery. If the alternator is good the engine should run on its own without the batteries. Give the alternator a good tap or hit depending on your feelings for it. The batteries are just for start up. That's what I did on my gasser but I assume it should work for the diesels as well. I had the exact same issue of intermittent alternator problems. All the tests said it was fine. My ****. Did this test and engine died. Bad alternator. Don't trust the tests.

 

I had some autostore employee tell me the 3G for my 4.9 was bad, it was new in box, but possible due to freight. Just wanted to test before install. I watched the second retest, told her to try plugging in the stator for the third test...shockingly the alternator worked fine. Told me 'oh, I did not see that plug there'. So I said 'why else would that wire be in the test harness?' Moron. I almost always try to deal with the older guys at the auto stores, they actually know stuff.

Check for 12V at that green plug on the regulator plug key on. One runs back internally to constant 12V, usually yellow. White is the stator wire. Also check output on the +B post on the thing when running. It is possible the fusible link is smoked or you have surface caca on the ring terminals preventing it from charging.

Also, the alternator grounds to the bracket. May want to pull it, clean where it mounts, reinstall.