Turn signal electrical problem
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Joined: Dec 2010
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Turn signal electrical problem
When I turn the lights on in my 79 F-150 my left turn signal light comes on and stays on as long as the headlights are on. The light is only on on the dash not outside. When I activate the left signal the light blinks. The front signal does not function and the bulb is not bad. Has anyone had a problem like this? Is it the relay or a wiring short?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
This is a textbook example of the front turn signal socket(s) gone bad. The ground out at the socket has opened up, and the parking lights are back feeding through the dash turn signal indicators as the current tries to seek a ground. This is supported by the fact that the front doesn't light up, yet the bulb is good. Replace both turn signal sockets (front left and front right). This is almost always the case when there is an interaction between the parking lights and the turn signals, because of the dual-filament 1157 bulbs used in the system.
There is no relay in the turn signal system. The flasher is not a relay because it is in series with the switched circuit; there is no separate control circuit.
There is no relay in the turn signal system. The flasher is not a relay because it is in series with the switched circuit; there is no separate control circuit.
Mountain Pass
Joined: Jan 2012
Posts: 243
Likes: 16
From: Estacada, Oregon
What FMC400 said, I just had the same issue on my 77. Replaced the sockets (I did both as well since I had to replace one anyway) and everything is good again.
This is a textbook example of the front turn signal socket(s) gone bad. The ground out at the socket has opened up, and the parking lights are back feeding through the dash turn signal indicators as the current tries to seek a ground. This is supported by the fact that the front doesn't light up, yet the bulb is good. Replace both turn signal sockets (front left and front right). This is almost always the case when there is an interaction between the parking lights and the turn signals, because of the dual-filament 1157 bulbs used in the system.
There is no relay in the turn signal system. The flasher is not a relay because it is in series with the switched circuit; there is no separate control circuit.
There is no relay in the turn signal system. The flasher is not a relay because it is in series with the switched circuit; there is no separate control circuit.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It's not too bad of a job. Each socket has 3 wires; just keep track of which is which. I recommend soldering and shrink-wrapping the wires; don't use the butt splices that come with the new sockets. Butt splices should never be used on exterior or under-hood wiring.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I buy almost everything online from Rock Auto nowadays. In my area at least, one of the stores near me would have one socket, but I'd have to drive 15 miles in gridlock traffic to get to the store that had the other one. I got tired of an entire Saturday going to parts hunting; the shipping cost is worth it.
Junior User
Joined: Jan 2008
Posts: 71
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From: Andalusia AL
Just an update; I soldered up the front turn signal sockets on my '79 today they had the part in stock at my local parts store. Dorman Part # 85898, Just be sure to look it over good before wiring it up. The color code is not the same as Ford. That fixed my problems! Well except for a dash light and the "previous owners" butchered up trailer lights lol.
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