Turn Signal Issues
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New User
Joined: Nov 2009
Posts: 3
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Turn Signal Issues
Recently bought a 78 F250 4x4 and am trying to sort out electrical issues. I have one left and it is really stumping me.
My turn signals stop working as soon as I turn my dash-lights on. The headlights themselves don't seem to effect it. With the dash-lights on both turn signal indicators on the dash will come on and stay that way, none of the actual turn signal lights will come on.
Also, using a test light both wires going to the signal flasher become hot when the dash lights are on, otherwise only the blue wire is hot.
anyone have any ideas?
My turn signals stop working as soon as I turn my dash-lights on. The headlights themselves don't seem to effect it. With the dash-lights on both turn signal indicators on the dash will come on and stay that way, none of the actual turn signal lights will come on.
Also, using a test light both wires going to the signal flasher become hot when the dash lights are on, otherwise only the blue wire is hot.
anyone have any ideas?
Junior User
Joined: Aug 2009
Posts: 95
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From: Holden
my 78 supercab does the same thing only it does it on just the right side. i cant figure it out.when i have no dash lights on my turn signals work great, but as soon as i turn on my lights my right indicator in the dash stays on and my right side signal stops working. please help
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New User
Joined: Nov 2009
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Check the turn signal socket on that side for corrosion and loose wires and check the bulb on that side.
The running light filament in the turn signal comes on when you turn your dash lights on and for some reason leads to that symptom if either the filaments are semi damaged or the ground inside the socket is iffy. (I'm horrible with wiring and just got lucky with a test light so I have no idea what actually causes it!).
You might be able to just turn the bulb a tiny bit to get it to work temporarily (one of mine started working after I played with it a bit)
The running light filament in the turn signal comes on when you turn your dash lights on and for some reason leads to that symptom if either the filaments are semi damaged or the ground inside the socket is iffy. (I'm horrible with wiring and just got lucky with a test light so I have no idea what actually causes it!).
You might be able to just turn the bulb a tiny bit to get it to work temporarily (one of mine started working after I played with it a bit)
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
This sounds like a ground issue at the turn signal bulb sockets. I'm assuming you replaced the bulb sockets, correct? Also make sure that the sockets are grounded to clean metal at the body, and make sure you have a healthy ground strap from the frame to the cab, and the engine to the firewall.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
D1FZ13234A .. Parking Lamp Socket-Plastic / Obsolete
Fits: 1975 F100/350 from serial number C50,001 & 1976/86 F100/350.
Fits: 1975/86 Econoline // 1978/86 Bronco // 1971/73 & 1976 Pinto/Bobcat // 1973 Mustang & Torino.
1973/74 and 1975 F100/350's before serial number C50,001: The metal socket is part of the metal parklamp body, the lens was available separately.
After C50,001, the parklamp body/lens is a one piece plastic assembly, the socket was available by itself.
Junior User
Joined: Aug 2009
Posts: 95
Likes: 0
From: Holden
got it fixed. I replaced the socket with one from a parts truck and it works fine. I was sure it was a ground problem but I guess not.
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New User
Joined: Jul 2012
Posts: 5
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From: ATTALLA, AL
I had the exact same problem on my 78 F100 Lariat with the left turn signal staying on. After reading a couple of these threads, I replaced the bulbs, sanded the ground areas. When none of this worked, I replace both left sockets and everything works perfectly now. Thanks so much for your posts. I would never have fixed it without them.
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