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2005 F-150 Electrical Issue

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Old 03-11-2008, 06:01 PM
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Join Date: Mar 2008
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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!!!

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Old 03-11-2008, 08:14 PM
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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.
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Old 03-11-2008, 08:52 PM
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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

2014 Platinum 4x4 SCrew 3.5L EcoBoost, A.R.E. Bed Cap, Line-X Bed, Paint Protection Film
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Old 03-12-2008, 12:03 AM
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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.
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Old 03-12-2008, 07:03 AM
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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.

If your original owner's manual is missing, download a soft copy from www.fleet.ford.com under the PARTS AND SERVICE tab.

1995 Mustang GT Convertible, only 68K miles. 2000 Ford Contour Daily driver.
2001 F250 SD, 6.8L, 4 X4. 2007 Mercury Mariner AWD - Wifey's daily driver,

Timesert 5553 kit available for rent, PM me.
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Old 03-12-2008, 08:22 AM
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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.
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