[johnkosir]

My left turn signal does not work, my right does. The left indicator on the dash turns on, but does not blink, 
    Micro Switches provide power to marker turn signal board
4 ways work left front signal blinks with flashers
Blue wire from fuse 42 in front panel to flasher
Blue wire from flasher to terminal 25 front panel
Black wire from front panel to connector on steering Colum
Yellow wire from connector to turn signal switch flasher power
Gray wire from switch to connector for left rear direction signal light
Green for left front from switch to connector for left direction signal light  
black wire is for rear left turn signal from front panel to back relay for turn signal
White from connector to front panel for left front
white with black stripe is for front left turn turn signal 
712 was built with led flashers
front leds plus rear relays are what make the flasher pulse
old led bulbs drew 30t-50% more power than new ones which was enough to make flashers work
some leds in my left turn signal bulb must of burnt out causing current to drop and it not to blink on left turn but blink with the 4 ways extra load from right bulb
the extra flashers the PO added made it do weird stuff
when I put in new bulbs it did not work called tech support for Truck Lite and they told me new leds used 30-50% less power than old ones
bought 2 different new flashers that were advertised for Led bulbs both did not  work
called Newell was told they put resistors in parallel  with the light if it does not flash that is what I did
Bulb is 1/4 turn to get out
      tool to get bulb out 2" plastic pipe with a piece of 2" pipe with 1" cut out of it compressed with channel plyer's and put in side the first pipe then 2 pieces cut off leaving 2  3/8" pieces trimmed to go in light
    2 nd piece pushed down into 1st piece
    finished tool 2 screws to stop it from turning hole drilled in case I need more leveraged
    I used this light following the circuit to see when it would stop working it never did when I got to the connection before the bulb the bulb would flash checked the  ground  it was good. Put a new bulb in it would not work, this was when I called tech support, 
    I did not need the scope but I was hoping someone could see something wrong in the trace and tell me what to look for


relay in front is pulsing
   

    PO added this don't know why  This was part of the problem

[Richard]

Do you have cornering lights at the front? Sometimes those were activated by the turn signals. That is just a WAG.

[cwl1979]

Do the lights outside flash? Does one stay bright all the time? could be that the dual filament is causing it to draw because one of the filaments is touching the other.

[johnkosir]

Kenworth direction signal control 4813-83 $75 on Ebay

[johnkosir]

If you have front entry and you turn the panel to work on it, you should check the large power wire for a nick in the insulation       mine had a nick in it that i taped over