F350 Headlights Got Very Dim

 
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coaledsweat
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Post by coaledsweat » Wed. Dec. 17, 2014 5:41 pm

2002 F350, the headlights were dim Monday. Tuesday they got dimmer. Both high and low beams are doing it. Checked the alternator, it is 14.02 volts so that should be good. Tried to read the voltage at the bulb and must have touched something wrong, no high beams now. Even the HB indicator on the dash is out. 30 amp fuse looks good. Finagled with a few wires figuring it was a ground issue. What say you wizards?


 
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Post by Rob R. » Wed. Dec. 17, 2014 5:51 pm

Start with the grounds, then the switch.

Does this have a plow harness on it?

 
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Post by coaledsweat » Wed. Dec. 17, 2014 6:33 pm

Yes, Minute mount Fisher plow. Plugged it in and it does the same thing.

 
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Post by WNY » Wed. Dec. 17, 2014 7:15 pm

check the voltage at the headlight when on, maybe a wiring harness or bad Relay if they use relays for switching. fuse might be good. Grounds are also good to check.

 
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Post by VigIIPeaBurner » Wed. Dec. 17, 2014 7:25 pm

Do the newer Fords still have the solenoid on the firewall? Older Fords (90s thru 60s) I had would act up and I'd pull the solenoid off the firewall, sand both to bright and it'd often fix a lot of crazy stuff. They were fussy on the grounding cable too. Check wiring harness connections going thru the firewall. Wiggle one wire at a time if you can. Might help isolate it there ... ? Did you check the battery voltage? Might have a cell shorting out but that should show on cold cranking.

 
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Post by coaledsweat » Wed. Dec. 17, 2014 7:35 pm

The motor spins over like a top. Battery is about six months old and charging at 14 + volts. In the morning I am going to unplug the plow haness and plug the lights back up OEM to isolate the problem. Plugging in the plow causes relays in the plow harness to switch from truck to plow lamps.

 
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Post by Rob R. » Wed. Dec. 17, 2014 7:56 pm

I suspect the plow harness and/or relays.


 
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Post by SMITTY » Wed. Dec. 17, 2014 9:12 pm

Yep - I'd put money on that.

Sometimes people wire them so they ground through the plow attachment to the truck .... then as you plow up all kinds of salt, and it sits overnight ... or a week .. and corrodes up like a zinc anode in Boston Harbor, the ground connection is compromised. Seen this several times.

Seem to see lots of hacked-in plow wiring jobs too. Got to use dielectric grease on EVERY connection, and EVERY ground to the frame. Also got to use weatherproof connectors, or solder - not those crap auto parts store yellow/blue/red connectors that are exposed to everything. Plow electrics need to be treated like boat electrics.

 
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Post by coaledsweat » Thu. Dec. 18, 2014 5:15 pm

Bypassed the plow harness, does the same thing. I'm thinking headlight switch now.

 
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Post by coaledsweat » Sat. Dec. 20, 2014 12:33 pm

Ok, looks like they're fixed. There are actually two fuses for high beams. A 30 amp for "high beams flash to pass"and a 15 amp for high beams. The latter was blown. That would fix the high beams being out but oddly enough, it appears to have fixed the dim light issue too. Since there is no fuse labeled for low beams, I really don't understand why they are both back to being bright unless fiddeling with the wires corrected a bad connection. The spade terminals on the fuse did appear to be a bit mungy though but when blown, I still had low beams. Weird.

 
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Post by VigIIPeaBurner » Sat. Dec. 20, 2014 2:13 pm

Could be the voltage from the complete circuit flowed back thru the open circuit via a common ground.

 
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Post by coaledsweat » Sat. Dec. 20, 2014 2:39 pm

VigIIPeaBurner wrote:Could be the voltage from the complete circuit flowed back thru the open circuit via a common ground.
The high and low beams were both dim when this adventure started. I just managed to blow a fuse and knock out the high beams trying to find out why.

 
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Post by coaledsweat » Sun. Dec. 21, 2014 5:23 pm

Well they are still dim, both high and low beams. Have 14.2 at the battery and 14.2 at the ground leaving the lights. Added a wire from there to the ground post on the battery..... still dim. What are the odds four lamps getting weak all at the same time? I probably have better odds with Mega Millions! Not sure what to do but will try new bulbs tomorrow.

 
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Post by Dave 1234 » Sun. Dec. 21, 2014 5:49 pm

CS, It will not be the bulbs. You have low voltage getting to them.
With the truck running and lights on, test voltage back from the bulbs twards the battery. Someplace along that circit there is a bad connection. Double check to see if the ground from the headlights to the radiator support is ok. A short piece of temporary wire to jump around any components like the fuse block will really help .

Good luck !

Dave

 
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Post by coaledsweat » Sun. Dec. 21, 2014 6:33 pm

I ran a new wire from the headlight ground at the lights to the battery negative post. I'm getting 14.2V at that ground wire. I would say enough voltage is getting to the bulb if 14.2V is coming out of them, right?


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