2005 F-150 Electrical Issue - F150online Forums

Go Back  F150online Forums > Body > Electrical Systems
2005 F-150 Electrical Issue > 2005 F-150 Electrical Issue

2005 F-150 Electrical Issue


Old 03-11-2008, 07:01 PM
Junior Member
Thread Starter
Join Date: Mar 2008
Posts: 2
2005 F-150 Electrical Issue

Randomly my lights, inside and out will dim for aprox 5 seconds and then go
back to normal, the blower will slow also if it's on. I have tried to shut
off everything and this still happens. The dealership has changed the
battery, (because it was a little low??) but can't find anything else wrong.
I notice this more at night, steady highway driving, sometimes at a stop
light, but basically random.

Isn't there something that can be hooked up, say via the cigarette lighter,
to monitor and log the voltage? My dealership says there isn't, but I have a
volt meter that will show peak voltage, you'd think they would have one that
could do low or high voltage. They said the monitor won't log in the
electrical system.

I'd think that there is a problem in the charging system, maybe the
alternator is overloading and shutting down for 5 seconds, so I am going to
battery power then back to alternator. But I don't know, I'm not a auto
mechanic. But I have mentioned it to the service manager, but he says that
if he can't replicate it he doesn't know what else to do.

They have the truck now, overnight, and will probably call me in the morning
to tell me they can't find a problem, but it's still going to be a problem
it has for the last 2 years off and on.

Help Please!!!

Reply With Quote
Old 03-11-2008, 09:14 PM
Technical Article Contributor
Join Date: Jun 2002
Location: Under the flightpath of old ORD 22R
Posts: 10,510
You could take your alternator to Napa or a similar palce to have it tested, but it might test OK ?? Don't know if the load test would find this problem.

Dumb question time, have you checked the Pos and neg leads on the battery, as in all points on both ? Might be worth a try to see if it is a loose connector ( would expect this to be more then here and there for the problem ) or frayed connector on the cable ? This woudl require crawling under, and checkign the ground side as well.

OBD-II / CAN scanning and logging software for laptops start about 130.00 and go up.

Old O-Scopes and the Vellman personal O-Scopes are in the 100.00 to 150.00 range.

Tough call, considering the dealer might not even know how to capture this problem ( they woudl need the Autotap type software and see the problem, or leave it in the truck while you drive it ), after a visual on the cables and connectors on the Pos and Neg cables, and having an Alternator test done, do you spend the money on the test equipment to diagnose the problem, or do you take a swag at it is the alternator, and replace it, in hopes this is the problem ???

I would start with checking the cables and connectors, and then take the alternator in for a test, before making that choice, you might find a bad cable, or problem under load with the Alt.

Someone else might have a better idea...

Good luck.
Reply With Quote
Old 03-11-2008, 09:52 PM
JackandJanet's Avatar
Global Moderator &
Senior Member
Join Date: Aug 2007
Location: Among javelinas and scorpions in Zoniestan
Posts: 6,976
If you had an Edge programmer, and had one of its gauges monitoring voltage, you would probably see a fairly significant voltage drop when your lights dim. But, this would not tell you the source of the problem.

I really can't see this as a problem with your alternator or your battery. In my somewhat unschooled opinion, I think you have some device in your truck that is coming on briefly and is sucking alternator power during your "dim" periods. I used to see this in older vehicles when the air conditioner would come on (this was back in the days when air conditioner compressors were "cycled" on and off with a clutch - who knows what they do now?)

As far as reading voltage, you COULD connect a voltmeter to the battery and run the test leads inside your truck through the passenger window. Put the voltmeter on the dash. Then, you could get an accurate read of the voltage while driving. I did something like this when I was troubleshooting a faulty tachometer on a Ford Thunderbird back in the 70's. I had a "replacement" tach in the instrument panel and my old tach on the dash. BOTH malfunctioned at the same time, telling me (and the dealership) that the problem was NOT in the tach. Saved me some money.

- Jack
Reply With Quote
Old 03-12-2008, 01:03 AM
Senior Member
Join Date: Jun 2006
Location: Toronto, Canada
Posts: 451
im gonna suggest something no one else has thought of, and say maybe you have a short somewhere in the system. not a big enough one to blow anything, but just one little strand of a wire causing you all this grief.

and i will mention checking the ground connection, making sure its solidly bolted and has nothing obstructing it.
Reply With Quote
Old 03-12-2008, 08:03 AM
Senior Member
Join Date: Oct 2002
Location: St. Louis (Out in the woods)
Posts: 6,274
I'd bet your alternator is simply dropping out intermittently.

For $15, you can pick up a voltmeter that plugs into the cigar lighter. I got one when my 94 SHO was exhibiting the same symptom without a warning light.

I completely doubt that any type of short could cause this, they simply don't work this way.

Reply With Quote
Old 03-12-2008, 09:22 AM
Junior Member
Thread Starter
Join Date: Mar 2008
Posts: 2
Thanks for all the help, I had thought about the compressor drawing hard on start up, say for the defrost, this is why I had everything off except for the headlights and dash lights. I do think I will try the volt meter suggestion, I have one and I also have some spare cigerete lighter plug in's, I should be able to rig up something to make it work so I can view it inside the cab.

We'll see this morning what the dealership says.

Btw this is under warranty, I don't want to spend any of my money, cost enough for gas to drive it... Just want to give the service manager some ideas, he seams to be giving up pretty easy...If I find somthing I will post it.

Again thanks.
Reply With Quote

Related Topics
Thread Starter
Last Post
2004 - 2008 F-150
12-29-2017 06:16 PM
05-03-2016 02:00 PM
Electrical Systems
07-28-2015 05:12 PM
Electrical Systems
07-20-2015 10:45 PM
Electrical Systems
07-13-2015 12:10 PM

Thread Tools
Search this Thread
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


All times are GMT -4. The time now is 09:15 PM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
  • Ask a Question
    Get answers from community experts
Question Title:
Your question will be posted in: