Exhaust brake: 12V keyed wiring

[Blue Goat]

I have been reviewing the installation manual for the 2003 Jacobs exhaust brake. The manual directs the installer to splice into a factory harness to aquire 12 volt keyed power. Is there another option(fuse box) to gain 12 volt keyed power without splicing?

 

[Casey Balvert]

I have the brake on order through my dealer and have downloaded the instructions. I noticed the instructions to splice as well. I am not comfortable with splice there either and not really sure why they recommended that particular spot, except that it is close to the exhaust brake. Personally I would rather run a wire to the inside and splice there as there are plenty of sources for keyed 12 volt there and it is out of the elements. There might be other spots too but since I don't have the wiring diagrams yet, I am in the dark.



Casey

 

[Dean Upson]

I am not very well versed on the electrical end of these trucks, so if this sounds foolish just consider the source. Could it be that the connection is at the fan because the brake will cut itself off at idle at 170-175 degrees (page 16 of the installation manual)?



Dean

 

[Casey Balvert]

I would think that function would be controlled by the ECM connections. Again without the wiring diagram I can't tell what the actual source is for the wire that they are recommending.



Casey

 

[Blue Goat]

I believe the logic in the ECM controls when the exhaust brake is actuated. The exhaust brake will actuate at idle as long as the engine temperature is below 170-175 deg. F and the Stalk switch is on. This is for engine warm-up.

 

[Dean Upson]

Your explanations make a lot more sense than mine did!



Dean

 

[Blue Goat]

The new brake involves two pins on the ECM and a relay to pull in the solenoid. This is different form the 2nd generation brakes. The 12 volt keyed power is supplied to the light on the stalk switch and to pin B42 on the ECM. It could also be used to apply 12 volts to pin B39 on the ECM when the stalk switch is activated, but I am not positive. Not sure about how the logic works between the two pins.

 

[Casey Balvert]

Wow. So does that mean it does not matter where the keyed 12 volt power is derived from? I would guess it doesn't matter.



Casey