astro van lights out

Hi guys, If someone could point me in the right direction I would appreciate it. I work at a dealership in the body shop. Long story short. We worked on the front end of a 2000 Astro van with alarm, remote start, etc. The system was installed awhile ago and now we were just repairing collision damage. When checking out the lights,horns,etc, we noticed that when the headlights are on and you honk the horn,the headlights go out. Only for the moment you press the horn pad. Also on the dash the left turn signal indicator blinks and the high beam light flashes. Only when you honk the horn. Any ideas?

Sounds like a wire in the engine harness may have been damaged.  Which sucks considering how thick that thing is.  Good luck with it.  Wish I could help more, put that's not a car that I've dealt with enough to tell you exactly where the problem will lie.Cause I'm So white and nerdy...

First Class Certi-fried installer

Most likely nothing to do with the R/S system-- look for a common ground connector that are not attached to a ground post- like right in front of battery- there should be several on the one ground post- if you replaced the radiator support- you may have not transferred all the ground terminals- and the headlight ground and horn relay may be on the same ground- touching each other, but not a body ground--,, just a thought....Brcidd - Engineer That Does Remote Starter Installs on the side.

Just delivered it today and you are correct. There are two ground wires, in front of the battery just as you said, one comes off the negative cable and that was connected. The other one is held on by a 10 mm. bolt and it was hiding under the battery not connected. Grounds can sure do funny things. Thanks for the help. Working at a dealership makes us biased and quick to blame the aftermarket installers.  I think that most of you guys, as in my trade are qualified and try to do the best job they can do. Thanks again. Bondojoe