Suggestions…
 

Here is what I need to do…..I have to run a flat 4 trailer wire from the front of my 2011 HHR to the rear lights. So what the best way to route the wire under the car out of harms way and then inside to the existing tail lights

What's wrong with under the carpet with all the other wires?

I could do that I guess….only issue with that is I would have to come thru the firewall with it some where. I really dont have a need the wiring inside the car although it would be protected that way. Con is….be another potential leak.

Just use a quality silicone sealant @ the entrance point.
Clean the surface around the hole with alcohol or acetone if it is factory paint before sealing..

I use Marine clear silicone.

Silverfox

anyone know if there is a rubber bulkhead grommet to route my wires thru in rear of the car?

Yep. Several back there.

What wires need to go through the firewall? The BCM is right there with spare fuse positions.

Curt and I’m sure other suppliers have plug and play harnesses. Easy to install and run the harness out the hatch to the trailer wires

https://www.chevyhhr.net/forums/how-...-wiring-32903/

Now if you’re connecting to the tail lights to harness up to a motor home in a flat tow set up, that should work just disconnect the HHR body side of the light harness.

There are wireless options, too. Cheaper than the wire.

I meant the brake/tail lights are controlled by the BCM, no need to run wires to the rear.

that is exactly what I have in mind….with diodes to prevent back feeding to the rest of the car’s wiring harness. Just need best location to route the flat 4 trailer wires.