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Topic: Double checking my brake controller install (Read 303 times) previous topic - next topic

Double checking my brake controller install

VC-22RD chassis (hydraulic brakes), made the following connections:
Power and ground, blue to the trailer brakes, red to brake light wire going into one of the rear brake lights.
I know the vac pump under the hood that supplies the AC control also provides some vacuum to the brakes, but here's where it got weird.  Ignition key on, if I step on the brakes or use the manual override on the controller, another pump sounding something comes on from under me.  I am assuming this is another electric pump for the brakes.  I've just never hit the brakes with the engine off so I never heard it before.

So two questions, am I right that is another brake pump, and is it ok that it comes on when I hit the manual override on the controller without hitting the brake controller? 

Re: Double checking my brake controller install

Reply #1 –
Quote from: Paul GA –
VC-22RD chassis (hydraulic brakes), made the following connections:
Power and ground, blue to the trailer brakes, red to brake light wire going into one of the rear brake lights.
I know the vac pump under the hood that supplies the AC control also provides some vacuum to the brakes, but here's where it got weird.  Ignition key on, if I step on the brakes or use the manual override on the controller, another pump sounding something comes on from under me.  I am assuming this is another electric pump for the brakes.  I've just never hit the brakes with the engine off so I never heard it before.

So two questions, am I right that is another brake pump, and is it ok that it comes on when I hit the manual override on the controller without hitting the brake controller? 
It sounds like your controller is powering the light circuit when you press the override. See if the tail lights come on when you press it.  The sound is probably the brake boost pump turning on because it thinks you are on the brakes.  You could add a diode to the wire going to the brake controller to prevent this if needed.

Re: Double checking my brake controller install

Reply #2 –
So think I have it figured out.  The brake pump relay, and the brake lights (as well as my brake signal connection) are on the brake pedal switch (provides power when pressed).  There is a flow switch that grounds the relay when there is no flow thru it (I am assuming from the hydro pump on the engine).  So if the engine and hydro pump are running, the brake pump relay will not be grounded and the pump won't run when I override the controller.

Re: Double checking my brake controller install

Reply #3 –
Quote from: kgrover –
It sounds like your controller is powering the light circuit when you press the override. See if the tail lights come on when you press it.  The sound is probably the brake boost pump turning on because it thinks you are on the brakes.  You could add a diode to the wire going to the brake controller to prevent this if needed.

The controller is supposed to power the light circuit when overriding, so the brake lights come on when applying the trailer brakes.  The issue was making sure I wasn't causing a problem with the electric brake pump, but think I have it now.

Re: Double checking my brake controller install

Reply #4 –
Quote from: Paul GA –
The controller is supposed to power the light circuit when overriding, so the brake lights come on when applying the trailer brakes.  The issue was making sure I wasn't causing a problem with the electric brake pump, but think I have it now.
That makes sense. I'm still trying to figure out what the brake system would need the vacuum for if it's boosted from the hydraulic pump on the engine. I wish I could find a schematic of that chassis, because I'm really curious now.