I have a 2001 Yukon cruise control issue. The cruise control will not engage unless I plug in the trailer light adapter. With the adapter plugged in, the CC works fine until I turn on the turn signal which disengages the CC. Also, if the headlights are turned on, the CC disengages and will not reingage until the headlights are turned off. I do not have to have a trailer attached, just the trailer light adapter. It is the factory connection, no mods have been made. I also have replaced the brake switch.

Was the trailer light adapter OEM, or aftermarket.....

If aftermarket, did problem occur after installation?

The trailer set up is all factory. This just started occurring a short while ago. I have had the vehicle 5 years and it has worked fine up until now.

Then it sounds like a backfeed problem, due to a bad connection or ground.....

Any suggestions on how to chase it out?

You start with schematics......it will be fun trying to find one with the trailer adapter......

You may also have it scanned for codes, especially "B" and "U" codes, that might give you a starting point...

Thanks, the search begins