Troubleshooting Brake Controller Install Where Controller Stops Working with Blower Motor On

Question:

Hello, I have a 2004 Chevy, Z71, with a Reece Pilot brake controller. It only works when the heater/fan motor is off. It doesn’t matter if you use the brake pedal switch, or the manual slider on the unit. The pilot pigtail has four wires, and plugs directly onto the fuse box under the dash. Last fall, the blower motor resistor was replaced to repair the inoperative fan motor. I don’t know if the problem was initiated then or not, since this is the first time the trailer has been used for a while.

asked by: Dean

Expert Reply:

Hey Dean that is a really odd issue to have. I've been working in this department since 2009 (I think) and this is the first time this specific problem has been reported haha. I would think it has something to do with the blower motor resistor repair that was performed. It's hard to say exactly what but maybe the mechanic that did the job got creative with some wiring and when the blower motor circuit is active it's somehow deactivating the brake controller power wire.

expert reply by: Jameson C

Dean

3/5/2024

Hello Jameson, and thank you for your reply. I would normally agree, but in this case, I was the mechanic (ASE for over 35 years), and the resistor wiring was plug & play, with an identical (in appearance) resistor. The only thing I will add, it was an aftermarket resistor, and not OEM. And like I say, I'm not sure the timing correlates with when I replaced the resistor or not, since the trailer hasn't been used since. The truck has been meticulously maintained, and there are no extra wires added, chopped, spliced, etc., under the dash. Nothing is burnt or melted in either of the fuse panels. No extra wires are plugged into any fuse connectors. When testing the brake application voltage, (with the fan motor off), it varies as it should. I'll continue to investigate, but it might be a while, since my son normally has the truck, and he's not home often enough to do much testing with it. Thank you for any insight! Dean.

Jameson C.

3/5/2024

@Dean That is super interesting. So when you say it doesn't work when the blower motor is on does the controller lose power or does it just not function yet still is powered on? If it has power I would check to see if your third brake light is functioning when the blower is on as well. Typically the stoplight activation circuit for brake controllers is tied to that circuit.

Dean

3/6/2024

@JamesonC The controller does not lose power. It is still illuminated. The digital numbers don't escalate when the brake pedal is depressed, or the manual lever is moved. And no voltage is being applied to the brakes. The only way it will work is when the heater controls are off. I'll look at the third brake light when I see the truck again, and try to get a little more information.

Jameson C.

3/11/2024

@Dean Thanks for the follow up. Yeah it definitely has something to do with the stoplight circuit (red wire) of the brake controller. Your generation of GM truck is notorious for having a similar problem but it's the third brake light fuse blows and it causes the brake controller to stop working just like what you described. I can't imagine your third brake light fuse is connected to the blower motor but it's too odd not to mention.