Electric brakes mystery

[noteven]

I hooked up the Big Toyhauler the other day. All lights and signals function correctly. But - no brakes. Hmmm....

I am a bit of a dummy when it comes to things electrical.

Here is what I know so far, with Hayes air/electric controller:

Jump 12v direct to the brake terminal on the trailer cord, brakes come on. Verified with one wheel off the ground and listening for magnets humming.

Test truck 7 way plug. 12v is present on the brake connection in the plug at all times. When trailer is plugged in it's brakes do not come on.

Cleaned connections in truck and trailer plugs.

13.5v at battery terminals on truck at slow idle.

12.6v at the blue wire coming out of brake controller at all times.

12.6v at black wire coming in to brake controller from truck.

0v at red brake switch signal wire from truck. 12v at this wire when truck brakes are actuated. Trailer brake blue wire volts do not change, stay at 12, brakes to not come on.

Disconnect Hayes, connect a simple Tekonsha controller.

All readings etc. identical to above.

Tomorrow I connect a 3rd known to be good controller from another truck.

No fuses blown.

Any and all ideas welcome.

Thanks

[noteven]

Got back at this today -

Intermittent continuity on the ground between the controller and the battery.

Fix it!

Thanks for your replies

[enblethen]

What happens when you apply the manual brake lever?

[noteven]

DrewE wrote:
Did you check the ground connections on both sides of the trailer plug (and through it)?

There is continuity through the ground connection.

I've been off this project for a couple days.

[DrewE]

Did you check the ground connections on both sides of the trailer plug (and through it)?

[enblethen]

Sounds like air is not getting to the controller or the controller diaphragm has issues.

[noteven]

wa8yxm wrote:

enblethen wrote:
Should not have continuous power on blue wire. It should only have power when brake pedal is applied.
What kind of tow vehicle?
Exact model of brake controller?

Actually many controllers put continous power on the blue wire, OPEN CIRCUIT (Trailer not plugged in it will read 12 volts if the controller sees that 12 volts (Well battery voltage) when it's not calling for brakes it flys the fault flag to alert you to a problem.

IF you put a load on it (Say a test light in parallel with your volt meter) you will see it go down like a rock in free fall for it's a high resistance feed... if you plug the trailer in the voltage approaches zero (you won't be able to measure it) I doubt it's light the test lamp.

One of the reasons you need both a volt meter (HIGH resistance or high impedance load (The two words apply to DC and AC respectivelly)often well over 100,000 ohms) and a test light (Low resistance load often closer to 1-2 ohms)

I wondered about 12v being "normal" with no trailer - I can't say if that is the case with the two controllers I mention in my reply above. I am calling Hayes tech support today.

[noteven]

enblethen wrote:
Should not have continuous power on blue wire. It should only have power when brake pedal is applied.
What kind of tow vehicle?
Exact model of brake controller?

It is a Kenworth T300, controller is Hayes:

Hayes air/electric proportional controller

I am going to call their tech support today.

The second controller tried was a Tekonsha 9030

[wa8yxm]

enblethen wrote:
Should not have continuous power on blue wire. It should only have power when brake pedal is applied.
What kind of tow vehicle?
Exact model of brake controller?

Actually many controllers put continous power on the blue wire, OPEN CIRCUIT (Trailer not plugged in it will read 12 volts if the controller sees that 12 volts (Well battery voltage) when it's not calling for brakes it flys the fault flag to alert you to a problem.

IF you put a load on it (Say a test light in parallel with your volt meter) you will see it go down like a rock in free fall for it's a high resistance feed... if you plug the trailer in the voltage approaches zero (you won't be able to measure it) I doubt it's light the test lamp.

One of the reasons you need both a volt meter (HIGH resistance or high impedance load (The two words apply to DC and AC respectivelly)often well over 100,000 ohms) and a test light (Low resistance load often closer to 1-2 ohms)

[enblethen]

Should not have continuous power on blue wire. It should only have power when brake pedal is applied.
What kind of tow vehicle?
Exact model of brake controller?