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Old Nov 21, 2008 | 10:26 PM
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99 F350

<HR style="COLOR: #d1d1e1" SIZE=1 itxtvisited="1"> <!-- / icon and title --><!-- message --><TABLE width="100%" border=0 itxtvisited="1"><TBODY itxtvisited="1"><TR itxtvisited="1"><TD vAlign=top itxtvisited="1">99 F350 signal lights flash normally on both left & right signals with all bulbs working properly, until I engaged the brake pedal at which time when I use either signal it begins to flash rapidly and when I let off the pedal, the signal flash rate returns to normal. Also if I turn on the lights, either dimmer or headlights the same rapid flashing will occur on either the left or right blinker. I replaced all bulbs, checked the grounds connection on both batteries and verified all fuses & relays are working properly. Need HELP, any suggestions?
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Old Nov 22, 2008 | 10:24 AM
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Originally Posted by ebs
...... I replaced all bulbs, checked the grounds connection on both batteries and verified all fuses & relays are working properly. Need HELP, any suggestions?
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Working properly when you have the other lights on or just by themselves? If the flasher relay is bad, or going bad, a slight additional pull of power, say the other lights coming on, can cause it start acting up. I would replace the relays and then try again. They are cheap and it takes a minute to change them out. Cheap fix or if not fixed, you aren't out of a bunch of $$ or time.
 
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Old Nov 22, 2008 | 11:09 AM
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Usually the rapid blinking is caused by a turn signal bulb being out. Since yours only does it when you hit the brakes, maybe you have a burned out brake bulb. Have you checked the brake lights lately?

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Old Nov 22, 2008 | 10:51 PM
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99 F350 Signal Lights

Working properly just by themselves. When I turn on the lights or when I apply the brakes, they began to flash rapidly. Thanks for the advice, I will check out the relays.
 
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Old Nov 22, 2008 | 10:54 PM
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Yes, I changed out all of the bulbs.
 
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Old Nov 22, 2008 | 11:51 PM
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I'll throw out two possibilities:

1) There is a bad ground and a bulb is grounding through the other circuit in that bulb's power side.

2) You have a bad turn signal unit on the steering column. If this is bad there are several things that can happen.

I don't see many replies to this thread so you must have stumped the experts!

Jock
 
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Old Nov 23, 2008 | 01:26 PM
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Thanks for your advice. I do believe that there is a strong possibility of a grounding problem. Everything worked fine until I replaced both batteries which powered down the truck. After installing the new batteries, I have been fighting this problem. I have changed every bulb & verified each one is operational. I will try to check out the ground on the batteries & make sure no wire somewhere could be grounding out the circuitry.
 
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