What aftermarket connector do I need for low beam headlight?

Check the HEAD LEFT LWR FUSE (15A) and the HEAD RIGHT LWR FUSE (15A).
These fuses control the headlights when they are on LOW. Though its rare for both fuses to blow at the same time, I need you to verify that they are working.
There could be a blown blub on one side and a blown fuse on another side (still unlikely).

If the above procedure does not reveal the problem try this:

With the headlights ON, check for power on the #2 RED wire on the left headlight connector to the low beams. Check for ground on the WHT/BLK wire on that connector.

Check for power on the #2 RED/GRN wire on the right headlight connector to the low beam. Check for ground on the WHT/BLK wire on that connector.

Remove the affected headlight and replace the headlight socket on the wiring harness. I've had to do this for both headlights. It's a design flaw by GM and cheap parts. The connectors are not insulated and oxidize. You have to place them with aftermarket ones. Simply pull out the wiring harness and snip the wires, use electrical wire twists to connect the new socket. Reessemble and you'll be good.

These trucks are known for bad multifuction switches.
the switch that i talk of is the signal switch , the handle is the switch, it bolts to side of steering column . this switch controls the signals and the headlights and high /low beams. the other thing is the headlight switch connector, the connector some times goes bad and starts to melt or just comes out of the connector. you will need to remove the cover to steering column, the screws are located under the bottom cover in holes. remove cover and check connector and then test for power if you have power going into switch but not coming out then switch is bad.

the last thing is to make sure the bulbs are good , make sure the headlight bulbs are good , and also the driving light bulbs, test for power at the connectors to those lights to.
You will need to do a little testing to find the problem.

I can find out which color wires are for which bulbs if that would help.

Replace the headlight dimmer switch on the steering column and check the connector to it fro signs of overheating, replace connector and switch as one repair. Do not use crimp connectors, solder all wires as needed and use shrink tube to insult the solder joints.

Obviously you have a connector which has come partially apart somewhere between the Headlights and the Headlight Switch. Most modern vehicles have several connectors between the Headlight Switch and the Headlights, Start at the Firewall Connector and work forward toward the Headlights making sure all connectors are securely mated. Another remote possibility is that you have fractured the "Low Beam Filaments" in BOTH Headlights. You don't mention how hard you hit the Speed Bump but if it caused the car to "Bottom Out" the front suspension it was a hard enough impact to fracture the filaments. You can use a 12 Volt Test Light at the Sockets for the Headlight Bulbs and see if you are getting 12 Volt power there. If you are in Low Beam position you have fractured the filaments. Check with High Beam too.

Since you've eliminated the headlight itself as the source of the malfunction, the problem is most likely the headlight bulb connector - the female connection inside the connector to the hi beam is good, but the connector supplying power to the low beam is bad. Your fix is to replace the headlight connector.
How: buy a replacement headlight connector at your favorite auto parts store, cut off the old connector, then (a) solder and heat-shrink or (b) wire nut and E-tape, or (c) crimp connector the new headlight connector onto the existing wiring (being careful to route the conductors to the correct wires on the connector).
Your cost: about $3 for a new connector

Removal & Installation To Remove:
WARNING
The halogen fog light bulb contains gas under pressure. The bulb may shatter if the glass envelope is scratched or if the bulb is dropped. Handle the bulb only by its base. Avoid touching the glass envelope.
NOTE: The headlight bulb should not be removed from the headlight assembly until just before a replacement bulb is installed. Removing the bulb for an extended period of time may affect headlight bulb performance. Contaminants may enter the headlight assembly where they can settle on the lens and reflector. Never turn on the headlights with the bulb removed.

1. Before servicing the vehicle, refer to the precautions in the beginning of this section. NOTE: Make sure that the headlight switch and the ignition switch are in the OFF position.
   
2. Remove the pin-type retainers, screws and the air deflector from the radiator.
3. Remove the three bolts and the headlight assembly.
4. Disconnect the electrical connector.
5. Remove the cover from the rear of the headlight assembly.
6. If equipped with HID, release the spring tabs to remove the low beam bulb, otherwise disconnect the electrical connector and remove the bulb.
7. Disconnect the electrical connector and remove the high beam bulb.

HID low beam headlight bulb

Standard low beam headlight bulb

High beam headlight bulb

To Install:

1. Place the headlight assembly in the proper position.
2. Install the cover from the rear of the headlight assembly.
3. Connect the electrical connector.
4. Install the three bolts and the headlight assembly.
5. Install the radiator air deflector.

You have a bad ground on the left low beam. Using a test light connected to ground see what wire is positive with low beams on. Using a piece of electrical wire connect one end to ground and with the headlight connector connected to the headlight and headlights on stick the other end into back of the connector at the ground wire. If the light gets brighter, you can cut the original ground wire to the connector ( 2-3 inches from headlight connector) and run a new wire from ground and connect it to the wire at the connector. Hope this is helpful.

Headlight's are not fused, there is a circuit breaker built into the headlight switch, pull the head light switch out and look for a burnt discolored connector and discolored terminals on the switch, if u find either or both replace the headlight switch and the connector, headlight switch connectors are avail in the aftermarket through full service parts stores like NAPA, also on the internet under automotive electrical repair connectors, if the headlight switch checks ok and has power in to it and out to low beams then replace the multifunction switch opn the steering column.