Brake/tail lights flickering when headlights are on

Printable View

June 14th, 2018, 06:08 PM
78FordF150

Brake/tail lights flickering when headlights are on

Need some help getting my stop/turn lights to work correctly. When I'm in service drive (first click on three way switch) the brake and turn signal work fine. When I turn it to the second click and turn on the headlights, the front and rear marker/turn lights both will blink when using the turn signal or brakes. I have replaced with new parts the rear lights and both turn signal switch and controller. I replaced the wiring harness between the switch and controller with a used one that I had along with trying two different used 3 way stitches that I had. Wiring along the frame appears to be intact. I did have to repair the rear wiring for the lights at the end of the frame so that all should be good. I'm assuming I have a short to ground somewhere, but I have had no luck finding it.

Sent from my SM-G930P using Tapatalk
June 15th, 2018, 01:36 AM
tomb

bad ground most likely on the head light system
June 15th, 2018, 10:58 AM
kwai

Could also be a weak alternator. Check your voltage with and without headlights on. You should be getting at least 28V when charging properly.
June 15th, 2018, 11:01 AM
78FordF150

Headlights is the only thing I havnt really looked at. I added new star washers to all four signal lights. I'll look at the headlights this weekend.

Quote:

Originally Posted by tomb

bad ground most likely on the head light system

Sent from my SM-G930P using Tapatalk
June 15th, 2018, 11:06 AM
78FordF150

Quote:

Originally Posted by kwai

Could also be a weak alternator. Check your voltage with and without headlights on. You should be getting at least 28V when charging properly.

I never even thought to check that. My alternator is covered in oil from a leaking power steering pump. I could see where that could cause it to deteriorate a little.

Sent from my SM-G930P using Tapatalk
June 15th, 2018, 02:40 PM
Barrman

If that all checks out then you are left with the 3 lever switch or under dash wiring shorts. Those are always fun.
June 15th, 2018, 06:59 PM
Don Cavey

If I remember correctly, there is a circuit breaker inside of the three-lever switch. That might be weak or you may have a pinched or corroded wire somewhere.

Just a thought...
June 15th, 2018, 08:12 PM
78FordF150

Quote:

Originally Posted by Barrman

If that all checks out then you are left with the 3 lever switch or under dash wiring shorts. Those are always fun.

That switch wasn't easy to get out for a fat guy. Lol

Sent from my SM-G930P using Tapatalk
June 15th, 2018, 08:14 PM
78FordF150

Quote:

Originally Posted by Don Cavey

If I remember correctly, there is a circuit breaker inside of the three-lever switch. That might be weak or you may have a pinched or corroded wire somewhere.

Just a thought...

That could be why I had 2 spares in a box of parts that I bought. Any way to bench test it? Didn't really see anything in the manual for it.

Sent from my SM-G930P using Tapatalk
June 16th, 2018, 12:42 PM
Barrman

At the top of the page is a link to maintenance manuals. One of those is called the M715 lighting diagram. Print it out. It is the best pin out for the 3 lever and turn signal switch I have found yet.

I have the best success with a DVOM that has the beeper on the Ohm setting. Just set the meter to the beeper, put a lad in the power in pin and the as you move the levers to different functions. Put the other lead in the appropriate pin. If it beeps all is good.

That checks basic functionality of the switch. Not the breaker inside the switch. I have no idea how to Amp check it. Sorry.