2007 trailblazer When you put my trailblazer in drive, the headlights are not coming on. We had transmission work done awhile back. Is there some kind of switch they may have dislodged?

Chevy Trailblazer 2002 2009 Factory Service Workshop repair manual

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sounds like a weak spring on the relay ?? but iam no doubt wrong ,if all else fails rewire the light switch through the ignition switch

I would check to make sure they are not burnt out, Then check my fuses, then check my switch.. It is a matter of elimination

Headlight Replacement (Trailblazer, prior to 2006)

Your grille and chrome bar are held to your truck with eight clips. You can see the top clips if you look. First VERY GENTLY!!! start pulling your grille until you start popping those clips out. Keep an eye on your chrome bar, because it is clipped into the headlight. GENTLY pull on the chrome bar at the headlight until the clips come off, then work your way over to the other headlight. The goal is to be take your time and be gentle until you have all the clips released. Set your grille aside(be careful not to scratch it). Each head light has two metal tabs on top of it, the outer tabs are slightly hidden in the fender. If you pull these tabs up, it will release the headlight from the frame of the truck(be careful not to let the headlight fall out and scratch your bumper). Once you have the headlight assembly out, pop off the circle rubber cover on the back of the unit. Your bulbs will be inside there, and make sure you don't touch the bulb when removing it. Just reverse the process when your done changing your bulbs. Don't forget to put the rubber cap back on the headlamp unit before you re-install it.

Your grille and chrome bar are held to your truck with eight clips. You can see the top clips if you look. First VERY GENTLY!!! start pulling your grille until you start popping those clips out. Keep an eye on your chrome bar, because it is clipped into the headlight. GENTLY pull on the chrome bar at the headlight until the clips come off, then work your way over to the other headlight. The goal is to be take your time and be gentle until you have all the clips released. Set your grille aside(be careful not to scratch it). Each head light has two metal tabs on top of it, the outer tabs are slightly hidden in the fender. If you pull these tabs up, it will release the headlight from the frame of the truck(be careful not to let the headlight fall out and scratch your bumper). Once you have the headlight assembly out, pop off the circle rubber cover on the back of the unit. Your bulbs will be inside there, and make sure you don't touch the bulb when removing it. Just reverse the process when your done changing your bulbs. Don't forget to put the rubber cap back on the headlamp unit before you re-install it.

Your grille and chrome bar are held to your truck with eight clips. You can see the top clips if you look. First VERY GENTLY!!! start pulling your grille until you start popping those clips out. Keep an eye on your chrome bar, because it is clipped into the headlight. GENTLY pull on the chrome bar at the headlight until the clips come off, then work your way over to the other headlight. The goal is to be take your time and be gentle until you have all the clips released. Set your grille aside(be careful not to scratch it). Each head light has two metal tabs on top of it, the outer tabs are slightly hidden in the fender. If you pull these tabs up, it will release the headlight from the frame of the truck(be careful not to let the headlight fall out and scratch your bumper). Once you have the headlight assembly out, pop off the circle rubber cover on the back of the unit. Your bulbs will be inside there, and make sure you don't touch the bulb when removing it. Just reverse the process when your done changing your bulbs. Don't forget to put the rubber cap back on the headlamp unit before you re-install it.

could be the fuse under the hood or the selector lever itself malfunctioning

The daytime running lights run the high beam bulbs at low voltage so it sounds like you need to put the relays back where they were and either replace the low beam bulbs or repair the wiring to them.Also the relay you removed could be defective.

You friend broke the low one way clutch. He was rolling backwards and shifted into drive and floored it before the vehicle came to a stop.

did you check the fuse's and or relays.