So, I'm trying to install a Hayes trailer brake controller in a 2007 Ranger 4.0 XLT. I'm down to the last wire on the controller that is supposed to go to the "cold" side of the brake switch down at the brake pedal. There are two wires. When unplugged from the switch, one is indeed hot (12V) and the other cold. However, when plugged into the switch, both wires are reading 14V without the brake depressed. When depressed, one wire stays at 14V, and the other drops to zero. This seems to be the opposite from how it's supposed to work. Everything I've read says that the cold side should go to 12V when the brake is depressed. I certainly don't want to tap into a wire that's hot all the time. Can someone explain this to my confused brain??

 

Engine running is the only time you should ever see more than 13volt in any vehicle, so a problem with your meter unless engine was running

Brake Pedal switch is actually 2 switches in one case, a switch for brake lights, and then a separate switch as a "sensor"

On a 2007 the Purple/White stripe wire is the one you want to tap on the brake switch, it will only have 12v when brake pedal is down, it runs to 3rd brake light on cab and rear brake lights

The "sensor" switch is a GROUND with brake pedal up and then 12v with brake pedal down, so it has 2 signals, grounded or 12v
Brake light switch is 0 volts or 12volts, 0 volts is not the same as Grounded

 

Thanks Ron!
For some reason, I was reading a voltage on both wires (purple/white and orange/purple) while they were plugged in, and with the brake pedal up. One meter lead was on the bare (stripped) wire, and the other grounded. I think a retest today is in order. I'll report back. Hanks again for your expertise and quick response. Have a great day!
Dan

 

OK, Ron. My truck must be a freak! So I reran the test several times, and I got very consistent results. There are two small wires running to the brake switch - a blue/white and an orange/purple. With my meter grounded and the other lead clipped onto the stripped wire, and the connector plugged in, ignition switch in Accessory (car not running), I'm getting....

orange/purple wire - 12V with no brake, 0V with brake pedal depressed (I'm 100% sure of this)
blue/white wire - 12V all the time, with or without the brake depressed.

The results are the same, whether the engine is running or the ignition is in accessory position.

I'm thinking that the organize/purple (which is the one that cycles) maybe feeds a relay that reverses the signal to the brake lights. Would that make sense?
the last thing I want to do is hook into a line that is always hot, and burn up my controller or brakes, or both. 😬

 

There is no relay in any vehicle's brake light system it would be unsafe

There are 5 wires on the Brake Pedal switch, 2 wires for brake light switch and 3 wires for Sensor
2 wires for brake lights are larger gauge(16)
3 wires for sensor are smaller gauge(22)

Yes, the SENSOR part would have 12volt on 2 wires with pedal up, and then 0volt on one of those wires with brake pedal depressed

Brake switch looks like this: https://cld.partsimg.com/image/uploa...pf506603_1.jpg
Has a 5 wire connector

If you can see the Numbers on the switch:
"1" is the 12v in from fuse 19 in cab fuse box
"2" is 12v out to brake light bulbs<<<<this is the wire used for trailer brake controller

"3" is 12v in from fuse 32 for sensor
"5" is a Ground
"4" is out to a few devices that need to know brake pedal position, i.e. cruise, ABS, Computer

Pull out Fuse 32 in cab fuse box and retest, if you now have 0v then you were testing sensor wires, and with fuse 32 out the only 12v at the switch will be on brake light wires

Found picture with numbers shown here: https://ic.carid.com/standard/items/sls247t_6.jpg

The trailer brake controller wire may be a smaller gauge than brake light wires, but that's OK as it is not using any AMPs thru that wire, its a monitor circuit, it monitors if voltage is present, it doesn't use that voltage to power anything

 

Hey Ron! Well, you nailed it. Turns out I was testing the sensor switch. Once I saw the brake light switch down below, I had an Aha moment. Thanks my friend. Shout out if you're ever down in San Antonio. I owe you several beers!

Dan in SA

 

Good work