2002 Express 3500 electrical problem (Cruise Control)

[CafeBonnie]

For a few months now, I've not been able to engage cruise control with the lights on.
When I have the cruise control on, and I turn on the lights, the cruise control function disengages.
A quick internet search revealed that many Express vans (GMCs as well) have a weak ground to the running lights. This made sense to me, since when I hook up my trailer, the turn signal (20 amp) fuse blows after several uses of the signals.
I decided today to add two 14 gage ground wires (fore and aft of the trailer harness into the trailer accessory wiring loom underneath the right hand panel that holds the jack, etc.)
I went for a ride and was delighted to find that my additional grounds had brought back my cruise control function with the lights on...
...unfortunately, the same modification caused my brake light fuse to blow when I depressed the brake pedal, and the turn signal fuse to blow after three cycles of the blinker.
I'm simply mystified. I can understand how adding aditional grounds would re-instate the cruise control, but not why it would blow fuses.
Would anyone like to take a crack at this?
Regards-
CafeBonnie

[brcidd]

Your problem is in your brake light/turn signal light circuit- blown fuses only happen when there is a "short" to ground, not a poor ground- the cruise control is disabled when you hit the brakes- the brake light circuit is activated and is shorting to ground- and affecting your cruise control. the light circuit is feeding some voltage to the brake circuit- thus disabling your cruise control-The common denominator in these two circuit is at each and every tailight bulb, or tailight circuit- including your trailer wiring harness connector. Look for proper bulbs, proper bulb installation, any cut, frayed, or damaged trailer wiring harness, any tee-taps on trailer harness under truck, that are exposed, corroded- (I never use T-taps- always solder) - unplug the entire trailer harness where it plugs in - at the jack stowage location- see if problem continues- to try to trace down the problem. It has been my experience that trailer wiring harnesses, and corrosion cause 99% of these types of issues- heck my old van's back-up lights were always on for a few days- when the lights were on-- found my 6 pin plug trailer connector extremely corroded- that was crossing up in behind the plug- where the wiring goes in- I always fill that area with dialectric grease- and still those plugs only last a couple of years- you can bet that if your trailer plug is more than a year old- it too may be filled with corrosion- look in where the wires go into the backside of your connector on the vehicle. Have fun....