I have an 06' F-350, 6.0 that is having electric issues. I put a new alternator on last week which seemed to fix the battery light but it only lasted 3 days & now the battery light is on again. I have had the alternator & batteries checked & they all checked ok. Anyone have any suggestions????

 

The batteries have to be checked totally iosolated from each other. If done the way they did mine at AZ, you didn't have a valid test.

 

Batteries need to be:

A) removed from vehicle

B) charged fully

C) load tested separately with a realistic load similar to what a diesel starter imposes.


One major issue: Alternator wiring - pigtail and also battery / alternator connectors.

Check link below.


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Test alternator output (voltage and current with a clamp on ammeter).

Give us data on voltage:

a) sitting still after 12 hrs no run / charge

b) key on, glow plug cycling

c) key on after 2 min

d) cranking

e) immediate voltage when engine catches

f) voltage at 30 sec intervals to 5 min after start.

It should be in the 14ish vote range then.

 

could be a bad alt out of the box.

 

I have the charger on the secondary battery tonight. I will check it in the morning while the primary battery is charging. I hit them with a load tester while hooked in circuit & they both tested bad so I will isolate them & check. I had the new alternator tested & it is good according to the tester. Thanks for the input.

 

If only 1 battery tests bad, replace them both. If not the older one will drag down the new one.

 

Roger that.

The older battery that is good is often fine for use in another car....


Mark:

If you are reading... the batteries that "dont test" for your truck is the perfect batteries for your inverter ---

free, and it is "good enough" for the job.

 

Replaced both batteries & the light stayed off for an hour & then back on. As I stated before, I had the alternator tested & now 2 new batteries but no cure yet. I guess it will head to the shop tomorrow to get a full diagnostics on it.

 

Before you run off to the shop check all of the grounding wires/straps. You might get lucky

 

I am willing to bet you (if it is not something simple like the grounding strap, contacts).

It is the pigtail.

If the pigtail is good, the other guess: another bad alternator.

 

We tested the output of the new alternator & it is only putting out 11.5 volts. The old alternator when tested was acting funny & spiking weird. I have some corrosion on the trailer plug so I am wondering if that would cause this to short out. I have checked all the ground straps I could find & they were good & clean. The only conclussion I could come come up is the trailer plug.

 

I am guessing alternator is the problem, especially if it is only putting out 11.5 on the test stand. On my 7.3, I went through 4 of them in about 10 days (was ugly). Also be wary of the control wires going to the alternator, not just the large power wire, and make sure the mounting area is clean, as the unit grounds through the body of the alternator to the engine.

The corrosion in the trailer plug on the back should have no real effect on the alternator, as all of those circuits are protected by fuses. A short would simply blow the fuse.

 

There have been a rash of bad alternators (including brand new ones) from what I see as sub-standard components.


11.5V?

What is the test procedure? Was it on car?

If it is ---- suspect a bad pigtail.

 

It was tested on the truck with it running. The weird thing is that the light started coming on while I was acclerating & then it would go off when I would stop at a light or sign. This is driving me nuts trying to figure this thing out.

 

Have the alt tested where you bought it, off of the vehicle. If it tests OK, do like gearloose said and get a pigtail.