prodigy P2 brake controller acting funny

s10texan1 wrote:
Hello All,

Installed my Prodigy P2 in my 2005 GMC 2500HD 4x4 ext cab today. Hooked up my brand new car hauler and tried it out. Here's what I found:

Set up the Prodigy like it said... 6.0 volts at full manual lever. When I did this, I could tell the brakes were engaging manually because the trailer would slow the truck down. OK, so that's good.

I drove around and everything felt ok. But, when I turned the headlights on, the display changed from the normal ".c" to "0.0". And more importantly, when I accelerated the display would show voltage: up to 5 volts max when I accelerated hard. It's like the Prodigy confuses forward inertia with stopping inertia and starts engaging the trailer brakes, but only with the headlights on. What's going on?

Thanks!

S10 texan

What did you use to connect the Prodigy to the truck wiring? If you used a harness to plug into the firewall connector I suspect you may have the wrong one. GM changed the pin connections between 2004 and 2005. The headlight circuit should have ZERO effect on the controller.
Also, as suggested, check the ground connection at the trailer. A bad ground could cause a "NC" (not connected) display, although the other symptoms just do not jive with that.