My screen is dark and the green led light is now yellow.

Keep things simple and make this much easier. You will need a test light and probe each of the wires and you will have to do each wire while the lights are on, then the brake applied and then the turn signal and you will be in business in short order. Be shure to make all connections secure and use shrink tubing to waterproof the wires.

i belive ur yellow is left green is right purple is license plate and the dark green may be a grd

With both tail light lenses removed locate the black with yellow wires and the dark green with brown wires coming out of the brake/tail/turn signal sockets.

The black with yellow wire will be the running lights or tail lights and the brown wire from the trailer harness will attach to it.

The green wire on the trailer harness will be the right turn signal and will be attached to the passenger side tail light harness dark green with brown wire.

The yellow wire on the trailer harness will be the left turn signal and will be attached to the dark green with brown wire on the drivers side tail light harness.

The white wire on the trailer harness is the ground wire and will need to be attached to a good ground. Is it pretty easy to crimp an eyelet onto the end of the wire and use a self tapping screw to attach it to the body behind one of the tail light lenses.

Here is a trailer light/wiring article I have done in the past. It has a couple of good tips you may find useful.

http://www.hotspotoutdoors.com/forum/ubbthreads.php/topics/1425999/1/Trailer_Wiring_101

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

I will assume that you have checked out the power cables and external cables. If this is the case you will usually notice an indicator light from your monitor. Universally it is yellow or orange when it has power, then turns green when it detects input from your computer. If the Led light doesn't turn green even when your laptop is already booted, your culprits would be your iMac's video controller or your monitor's input cables.

Constant 12v + orange
Switched 12v + yellow
Ground Black/white
illumination grey/black
dimmer brown/white
antenna trigger dark green
left front speaker + tan
left front - grey
right front + light green
right front - dark green
left rear + brown
left rear - yellow
right rear + dark blue
right rear - light blue

Check the Lamp if no picture, audio may be present. Screen is completely dark. Lamp LED flashes 2X every 5 seconds, Power LED flashes GREEN for 140 seconds then flashes RED.
Check the ballast if no picture, audio may be present. Screen is completely dark. Lamp LED flashes 3X every 5 seconds, Power LED flashes GREEN for 140 seconds then flashes RED.

1998 Chevrolet Blazer S-Series Stereo Wiring Constant 12V+ Orange Switched 12V+ Yellow Ground Black Illumination Gray Dimmer Brown Antenna Right Front Front Speakers 6 1/2" Doors Left Front (+) Tan Left Front (-) Gray Right Front (+) Light Green Right Front (-) Dark Green Rear Speakers 6 1/2" Rear Doors Left Rear (+) Brown Left Rear (-) Yellow Right Rear (+) Dark Blue Right Rear (-) Light Blue

*** 91 park ave with delco bose =

black = ground
dark green = lights on input
grey = panel lights
pink = on input
yellow = power input
orange = battery power input

nca = shield ground
tan = left fr spkr +
orange/black = left & right spkr -neg
lite green = right fr spkr +

nca = shield ground
dark blue = right rear spkr +
dark green/yellow = right & left spkr - neg
brown = left rear spkr +

purple/white = display dim output
pink = vehicle speed input
-----------------------------------------------------------------------
**** 91 park ave without delco bose =

purple/white = display dim output
pink = vehicle speed input

grey = left front - neg
tan = left front + pos
dark green = right front - neg
light green = right front + pos

black = ground
dark green = display dim signal
grey = panel lights
pink = power antanna
yellow = ign input
orange = battery power
light blue = right rear - neg
dark blue = right rear + pos
yellow = left rear - neg
brown = left rear + pos .

there YA go

It may very well be a connection issue with one of the wire connections as its not giving you a error code. I would double check the wire plug connections

Battery LIGHT GREEN (+)
Accesory BROWN (+) RADIO HARNESS
Ground BLACK (-) RADIO HARNESS
Illumination DARK GREEN/WHITE (+) RADIO HARNESS
Dimmer DARK GREEN/BLACK (+) RADIO HARNESS
LF Speaker (+) GREEN/RED
LF Speaker (-) LIGHT GREEN/WHITE
RF Speaker (+) RED/BLUE
RF Speaker (-) LIGHT GREEN/BLACK
LR Speaker (+) YELLOW/WHITE
LR Speaker (-) YELLOW/BLUE
RR Speaker (+) GREEN
RR Speaker (-) GREEN/BLUE