One of the headlights out replaced the bulb with no success.

If input power reaching till the head light then its mean head light bulb is damaged need to replace.
Hope answer the question

That Uhaul harness is the first thing to check. Next would be the ground wire/s at the rear lamp. Your problem is that when the head lights are off, the rear light is grounded the the headlights(no power to the headlights). When you turn the head lights on, you loose the ground because the headlights over power the rear ground. Your flasher is not the problem. Use the OHM part of the meter(lowest setting) to check for ground. Anything above 5 Ohms is a wire replacement.

Have you checked the fuse box for any blown fuses? If they're all good then you must have a loose wiring harness somewhere or a bad ground.

If Halogen light bulb:
Ok then this is either an issue with the headlight switch or harness to the headlights . We're these checked ?

Common for the wire harness on the switch to go bad. Inspect the wire harness where it clips on to the switch and look for any signs of damage.

The plastic heats up from the current running through the switch and causes it to melt and then you loose connection caused from melted plastic between the contacts from the harness to the switch.

There is a upgrade to the headlight harness which is larger then the ones that came with the Suburban to address this issues. You can get them at the dealer or NAPA i believe.

Good luck and keep us posted. Thank you for using fixya and stay safe.

Molson02536

REMOVAL & INSTALLATION Examples of various types of automotive light bulbs
Fig. 1: Exploded view of the front headlight assembly and related components
If equipped, open the headlight access panel by sliding the latch and lifting the panel upwards
Fig. 2: Exploded view of the headlight bulb, retainer and wire harness plug

1. Open the vehicle's hood and secure it in an upright position.
2. If necessary, open the bulb access panel by depressing the latch then lifting. To remove the bulb, grasp the retainer and rotate it counterclockwise to unlock it . . .
   . . . then withdraw the bulb from the headlight lens housing
   
   
3. Unfasten the locking ring which secures the bulb and wire harness plug assembly, then withdraw the assembly rearward.
4. Disconnect the electrical wire harness plug from the bulb and remove the locking ring as well. Unplug the wire harness from the bulb and either slide the retainer over the plug, or remove it from the bulb
   To install:
   
5. Before connecting a light bulb to the wire harness plug, ensure that all electrical contact surfaces are free of corrosion or dirt.
6. Install the locking ring onto the bulb, then line up the replacement headlight bulb with the harness plug. Firmly push the bulb onto the plug until the spring clip latches over the bulb's projection. WARNING
   Do not touch the glass bulb with your fingers. Oil from your fingers can severely shorten the life of the bulb. If necessary, wipe off any dirt or oil from the bulb with rubbing alcohol before completing installation.
   
7. Position the headlight bulb and secure it with the locking ring.
8. To ensure that the replacement bulb functions properly, activate the applicable switch to illuminate the bulb which was just replaced. (If this is a combination low and high beam bulb, be sure to check both intensities.) If the replacement light bulb does not illuminate, either it too is faulty or there is a problem in the bulb circuit or switch. Correct if necessary.
9. Close the bulb access panel and the vehicle's hood.

If your getting power at the headlight wire harness, then it's going to be the bulb it self, but make sure your checking the right 12 volt terminal at the plug. There should be three terminals there, there is a ground, 12 volt low beam, and a 12 volt high beam. If both the low and high 12 volts are getting power, then it's going to be the head light bulb it self that has reached the end of it's life time since the day time running lights are always on which is the high beams. Good luck and check the fuse box under the hood by the battery. 

Review this guide...

Fig. 1: Examples of various types of automotive light bulbs

Fig. 2: Exploded view of the front headlight assembly and related components


Fig. 3: If equipped, open the headlight access panel by sliding the latch and lifting the panel upwards


Fig. 4: Exploded view of the headlight bulb, retainer and wire harness plug


- Open the vehicle's hood and secure it in an upright position
- If necessary, open the bulb access panel by depressing the latch then lifting.

Fig. 5: To remove the bulb, grasp the retainer and rotate it counterclockwise to unlock it ...


Fig. 6: ... then withdraw the bulb from the headlight lens housing


- Unfasten the locking ring which secures the bulb and wire harness plug assembly, then withdraw the assembly rearward.
- Disconnect the electrical wire harness plug from the bulb and remove the locking ring as well.

Fig. 7: Unplug the wire harness from the bulb and either slide the retainer over the plug, or remove it from the bulb


To install:
- Before connecting a light bulb to the wire harness plug, ensure that all electrical contact surfaces are free of corrosion or dirt.
- Install the locking ring onto the bulb, then line up the replacement headlight bulb with the harness plug. Firmly push the bulb onto the plug until the spring clip latches over the bulb's projection.

WARNING:
Do not touch the glass bulb with your fingers. Oil from your fingers can severely shorten the life of the bulb. If necessary, wipe off any dirt or oil from the bulb with rubbing alcohol before completing installation.

- Position the headlight bulb and secure it with the locking ring.
- To ensure that the replacement bulb functions properly, activate the applicable switch to illuminate the bulb which was just replaced. (If this is a combination low and high beam bulb, be sure to check both intensities.) If the replacement light bulb does not illuminate, either it too is faulty or there is a problem in the bulb circuit or switch. Correct if necessary.
- Close the bulb access panel and the vehicle's hood.

Good luck... and remember rated my help!

chapmnfarm: your head lights use a "2" fuse system.
one for the left and one for the right.
The fuse box you are looking for is under the hood on the passenger's side. It is a black box roughly 8 inches long and 4-5 inches wide. When you remove the cover, you will see fuses and relays. What you are looking for is the section in the box which has a cluster of 7 fuses. 3 in one row and 4 in the other. On the outer parameter are two relays. The fuses you are interested in are located in the row of 4 fuses, with the two closest to the "L" shaped part of the box. Both of those should be 15 amp fuses.
The fuse below those should be a 20 amp which is the lighting switch and the one below it is a 15 amp which is for the interior lights and the clock.
Check your harness grounds in the engine compartment near the area you have the problem. There are ground wires which come out of the harness on both sides of the core support. The wires are black in color and have "EYES" crimped onto the ends of the wires. Both of them will probably be located about 4-6 inches below the upper tie bar on each side of the radiator. Odds are that the eyes will be large enough to pass a 6mm bolt through.
I hope what I have given you will resolve your problem. Lem me know,,good luck>>>>>>>>>>>>>>>

If all fuses and bulbs are fine, it's probably a problem with the wiring harness. Take it to the dealer. Wiring harnesses are not something to do by yourself unless you're experienced with wiring on the specific car.