Turn signals and brake light issue

[Longshot379]

2000 K3500, 7.4 4l80e

New multifunction switch, New brake light switch, grounds checked and cleaned, light sockets cleaned and checked, New TYC brand rear lights,new led flasher, led front bulbs.

The issue is when turn signals are on, front flashes like normal. Rear flashes both sides. Apply the brakes and everything goes steady and flasher hyperclicks. Turn signals also apply trailer brakes.
I have changed multifunction switch twice. Ran new grounds for rear tail lights( lights got brighter).

I'm tempted to order another multifunction switch from a different company and try it. But I wanted to see if someone else has run across this problem first.

 

[GoToGuy]

If your turn signals are wonky don't attach trailer. 1) reran new ground? Exactly like factory, getting feedback through wonky ground?
2) your trailer plug needs to be rechecked,or your tap for plug is wrong.
3) providing your taillights are wired and grounded correctly your problem is in the cab.
Are you following the wire diagram in service manual? If not your chasing your tail. Download it free on here/ forum.
What does the center high mount brake light do when braking, and when braking with turn signal on?
Your sure your turn flasher is correct, and functioning normally?
If your on second multiswitch, either it's not the multi switch or you made a mistake somewhere.
What was the cause for this maintenance?
Select turn signal come to stop with brakes applied, turn signal has priority on selected side. As shown in wire diagram.
Do taillights ground to same point? Try separate ground points. Just a wag.
Good luck.

 

[Longshot379]

The problem exists with or without multiple trailers. Trailers are fine.

Center high mount brake had a loose connection in the plug. That has been cleaned and repaired. The light now flashes with the turn signals and goes solid with brake lights with turn signals on. The flasher no longer hyper clicks when turn signals are requested with brake lights on.

Wires were cut at the rear bumper by p.o. at some point. I basically piggy backed a ground wire to original ground point on frame rail which improved the brightness of brake and tail lights but did not change the original issue. All other lights on the truck work as designed.

The cause for this maintenance???
To get my brake lights and turn signals to work properly. It's the last thing left after rebuilding the truck from bumper to bumper.

 

[Longshot379]

Ok. I fixed the turn signal problem. Removed the 2 scotchlocks that someone put in beneath cab connecting both sides of the turn signals together. Now I don't have rear brake lights( have center high mounted stop lamps). That should be easy enough to fix.

Thank you for your assistance.

 

[Onizukachan]

Thanks for coming back and reporting what you found! Some one someday down the road will google and find this and it will help them!

 

[GoToGuy]

I guess I wasn't clear the trucks trailer plug wire taps are making the trailer crazy.
Well done.