prodigy P2 brake controller acting funny

[s10texan1]

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

[s10texan1]

Ah, I'm not in Germany anymore. Back in the US of A. Better update my profile.

I did see a dually over there once. Once. lol

s10texan

[BenK]

What is it like driving a "2005 GMC 2500HD 4x4 ext cab" over in Germany?

Must be one of the biggest vehicles, other than commercial, out there, right?

[s10texan1]

Thanks Partsman!

I did some checking and yes, my wiring harness was not the right one. I think I must have taken this harness from my 2000 Chevy pickup when I traded it in and got this 2005 GMC, which would explain everything.

I moved the red wire to an different pin location (after looking up several pictures of Tekonsha wiring harnesses online), and now I get voltage readings when braking with the lights on or off. Turning the lights on and off makes no change to the brake controller display.

Thanks for the help people!

s10texan

[partsman01]

The following information is for the 1999-2002 wiring harnesses.

Pin
Wire Color
Circuit Number
Function
A
LT BLUE
1620
Stop lamps
B
RED
142
Brake controller 12?volt source
C
DK BLUE
47
Brake Controller output (Trailer Brakes)
D
BROWN
2409
Brake controller illumination
E
—
—
—
F
BLACK
1850
Ground
The following information is for the 2003–05 wiring harness.

Pin
Wire Color
Circuit Number
Function
A
BROWN
2409
Brake controller illumination
B
RED
242
Brake controller 12?volt source
C
DK BLUE
47
Brake Controller output (Trailer Brakes)
D
LT BLUE
1620
Stop Lamps
E
—
—
—
F
BLACK
1850
Ground
To modify a 12171982, 15366255 or 15086884 harness for use in a 2003–05 vehicle, switch the wires in cavities “A” and “D”.

To modify a 15085418 harness for use in a 1999-2002 vehicle (see model list at the front of this bulletin for applicable models), switch the wires in cavities “A” and “D”.

Warranty Information
When the correct wiring harness P/N is matched to the specific model year of the vehicle, everything works properly. Therefore, conversion of an incorrect wiring jumper to match the vehicle would not be considered a warrantable repair.

[partsman01]

Inspect the brake controller wiring harness jumper that is plugged into the vehicle relay block-body. The relay block-body is located under the left side of the instrument panel near the left kick panel, behind a plastic cover.

The 1999 though early 2003 wiring harness jumper that plugs into the relay block will have a reddish/brown 6-way connector and a tag with the last four digits of the wiring harness part number. Second design 2003–05 may have a white plastic connector with part number 5418 as well.

The 1999 jumper is/was P/N?12171982 with a pink/purple tag identifier of 1982. This number has been superseded to 15366255, with a pink/purple tag identifier of 6255.
The 2000 jumper harness is P/N?15366255. The pink/purple tag identifier is 6255.
The 2001-2002 jumper is P/N?15086884. The orange tag identifier is 6884.
The 2003–05 jumper is P/N?15085418. The orange tag identifier is 5418.
When transferring the brake controller with the wiring jumper attached from a 2001-2002 vehicle to a 2003–05 vehicle, a change to the jumper harness connector must be performed.

Object ID: 366012Click here for detailed picture of the image.

[partsman01]

Condition
Some customers may comment that when the headlamps or park lamps are on, the brakes on the trailer are always applied, or that the back lighting for the trailer brake controller only illuminates when the brakes are applied.

Cause
The cause of this condition may be due to wiring changes within the vehicle electrical system for the 2003 model year.

[s10texan1]

Well I got to changing the front rotors and pads and bleeding the brakes of my truck, so I didn't get much troubleshooting done on the trailer. But, I do know this:

- I have a plain Prodigy, not a P2. My bad.

- When the trailer is connected, I get ".c" and it stays that way whether the trailer is moving or not and whether I am braking or not. Except when I turn the lights on...

- When I turn the lights on, whether parking lights or headlights, the display on the Prodigy changes to "0.0" instantly. It will count up on its own or when braking... what I mean is, is that when the truck is just sitting there in park and I turn the lights on, the Prodigy will say "0.0" for a few seconds, and then it will start going up, like to "3.4" for no apparent reason.

- The brakes work manually, but apparently not with the brake pedal. But its hard to tell: At max voltage and full manual lever, the brakes just barely lock up on dirt (empty trailer). I think this is more a function of new brakes that need adjusted though.

- I only saw one ground connection on the trailer, and it had continuity all the way to the trucks bumper.

Thanks for reading!

S10texan

[consumeratlarge]

Maybe disconnect the harness from the P2. Put a meter on those harness pins as you apply brakes to see which wire is sending juice with the brakes. And also check if headlights on is sending any voltage to any pin on the P2 connector, it shouldn't, of course. On mine, it came with a generic connector going to bare wires, which can be wired in if the factory one doesn't make sense. Power, ground, brake switch can be easily found, and the trailer brake wire can be traced, and attached to the bare wire connector if all else fails. Got to have those brakes! I remember seeing more than one way to connect the 7 pin connectors, also, check that.

[s10texan1]

Oh yeah, good point guys I'll check the ground connections tomorrow morning. Bad grounds can do all kinds of strange stuff to electronics.

I used a pre-made harness. Plugged one end to the Prodigy, and the other to the wiring box under the dash. I looked and I didn't see a part number on it. I'll pull the harness out and compare the placement of the wires with how they should be for a 2005. Gotta find a wiring diagram on the web now.

Thanks!

s10texan

[carringb]

One of the sockets on the truck or trailer may have a bad ground, causing the taillights to back feed into then brake circuit.

[kaydeejay]

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.

[ScottG]

It should never apply brakes unless the brake lights are on. When it's acting funny that way I wold make sure they're not stuck on for some reason.
I would also clean out the 7 pin connector with electrical cleaner if it doesn't look clean.

[45Ricochet]

Yeah check your pins for rust etc. If that don't do it I'd re check the wiring to the harness with a DVM. Or drive only in daylight :W

[jerem0621]

May want to check the grounds on the TV and the Trailer. Bad grounds can do funny things to electronics.