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Voltage Problems

1995 F150 351W
I am having intermittent engine performance problems, getting codes for sensors having voltages out of range, and getting a high voltage reading on my dashboard. Battery is at 12.6V with engine off and 14.8V at idle. Battery is 5 years old and looks to be spraying out some battery acid (dry white specs on other parts). Alternator passed twice at NAPA, failed once at Auto Zone, and passed twice at Advanced. Voltage starts at 15.1 is regulated to 14.6 and is 14.0 under load. I had thought bad voltage regulator, now I am wondering if an old battery can cause this.

Thanks for the help!
 

DNFXDLI

The Token Canadian
Staff member
Check your cables and do a load test on the battery. 5 years is getting to the end of a typical starting batteries life.

Output voltages seem normal.
 

Fellro

Moderator
Staff member
Also, make sure the harness that goes into the side of the alternator is in good shape. They can get a bad connection and wreak havoc on things as well, one of them the harness can get hot enough to melt...
 

Big Jim F150

73-79 Ford Trucks Rock
I had gotten a little over 7 1/2 years out of the original battery in my 07 Chevy Colorado, and then I had a bad negative battery cable and my alternator was doing the same thing, until I replaced the battery cable for I had an indicator come on saying service charging system so I had the cable replaced when I had my oil changed, and that took care of my problem for once and for all. Albeit a Chebby, but in 2013 I had new battery cables on my 78 f-150 when I had ignition problems.smilieFordlogo smilieFordlogo
 
Well I went ahead and just replaced the battery. The voltage on my dash is still reading high. Harnes going into alternator looks fine. I'm going to replace negative clamp next. It is not making a great connection with he cables. I'll update after that, let me know if anyone has anymore ideas!

Thanks!
 

Big Jim F150

73-79 Ford Trucks Rock
Fordgirl

Just change both of your battery cables, and that should hopefully take care of your problem, especially with that loose battery terminal which will cause that problem, for I had that same problem with my 07 Chevy Colorado which is my daily driver, and I had replaced both cables on my 78 F-150 Ranger Lariat for they looked alright from the outside, but inside they were bad, I had that done while my truck was at the Ford dealer for ignition issues.smilieFordlogo smilieFordlogo
 

DNFXDLI

The Token Canadian
Staff member
Where exactly are you getting the "high voltage" readings from?...the numbers you mentioned are what you should be getting.
 
I wish I could replace the positive battery cable. It is harnessed in all the way to the starter, I would need a pro to do it.

I am seeing high voltage on the voltmeter on my dash. I believe this is alternator volts? It always was at the middle between R and M, now it is all the way at A (on NORMAL).
 

DNFXDLI

The Token Canadian
Staff member
If you are methodical, it shouldn't be too hard to do, just take your time.

I'm assuming that you have used an actual meter to get the readings you posted?
 

DNFXDLI

The Token Canadian
Staff member
I wouldn't be too concerned about the dash voltmeter if you are getting those readings from a VOM. , they are normal, the battery will normally see 14+ volts for charging...I'm pretty sure most alternators are rated at 14.4 volts.

The voltmeter on the dash reads whatever voltage the battery has or is getting.
 
So I've been dealing with coolant issues and haven't replaced any battery cables or clamps yet, but the problem got worse: drove truck to the gas station and I tired up fine twice, then wouldn't start to go home. Lights and everything would turn on, but NO NOISE. I kept trying and then all the sudden it started just fine. I have new battery in, new starter relay, and the alternator that passed, passed, failed, passed, passed during testing. Voltmeter on dash still reads high, volts will go erratic sometimes at a stop light and truck feels like it will stall, under load (lights on and rolling up window) lights will dim and voltmeter will go way towards negative on dash. I'm trying to not keep throwing parts in. Anyway to tell if it is bad battery ground cable or alternator, or maybe even something else?

Thanks!
 

DNFXDLI

The Token Canadian
Staff member
You need to look at the main cables...both the positive and the ground, they can be internally corroded.
 
So from my research, you can't really ever see problems with corroded cables. I'm going to perform a voltage drop test: positive on positive battery cable terminal and negative on other end of positive battery cable terminal on starter, hopefully it reaches. Sound like a good start maybe?

Also, I'm now getting codes for oil, coolant, and ACT sensors out of voltage range.
 

Fellro

Moderator
Staff member
Sure sounds like you have a grounding problem.
 
Sure sounds like you have a grounding problem.

smilieIagree smiliewhathesaid x2 - with the age of these trucks poor connections especially around earthing points probably account for 80 - 90 % of electrical issues ...... poor earths can lead to sensors breaking down before their time too so it pays to spend time going over those connections and give them a clean as well as putting a smear of dielectric grease on them as you make the re connections.
 

dustybumpers

don't play well w others
Follow the ground wire from the battery, down to the frame, and you will find your problem. Ford had a good idea, Make the cable bare, and ground the frame, then continue to the block.
The bad idea is the water run off from the tire and corrosion.
You need to replace the neg cable
I usually run a new cable from the block to the battery. I run a second cable with 2 bolt ends from the same bolt on the block back to the spot on the frame where Ford had the original ground. Make sure everything is shiny clean, and covered in dielectric grease.

I also run a 10 ga wire from the neg terminal over to one of the mounts for the wiper motor.
 

dustybumpers

don't play well w others
Looking back through your other problems with the truck, I think you have several bad grounds.

There is a ground for your computer on the driver's side hood hinge that needs cleaned
There is another ground for your fuel system behind your driver's side headlight on the inside of the core support That needs cleaned. This one you have to search for, it's near the top, is a 10 ga wire that pops out of the taped harness.

Grounds under the ash tray inside the cab have probably been used/broken over the years. check them, make sure they are tight, and hooked up
 

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