I'm having a hard time trying to figure out how to keep my brake lights from coming on when my retarder is activated. I've searched on here and read many posts about this exact situation, but after looking at my wiring schematic and trying to isolate what to disconnect without impeding the functionality of my retarder I can't figure it out.
Any help would be appreciated, especially those who have a u320 close to my year who may have done this exact thing.
I'll also attach a photo of the relay under my dash by the brake switches that I thought would do this by disconnecting, but it does not seem to keep the brake lights from coming on with retarder operation.
Why would you do that? The retarded is pretty strong so it might prevent a rear end collision.
I personally would feel uncomfortable with my brake lights being on with retarder usage. I suppose if you mostly use your coach on flat terrain than probably not a bad idea for your stop lights to come on. We mostly travel in the western states where the retarder is being used for miles on end descending grades. Retarder is activated just enough to hold back speed saving on service brakes. When and if I hit the service brakes I usually slow 10 to 15 mph that's when I want my brake lights to come on.
I'm doing it because I tow a cargo trailer and use a curt bluetooth brake controller and I feel I'm going to burn up my trailer brakes on long downhill descents when I'm using the retarder to maintain my speed but not brake hard
When I hooked up a brake controller I put in an extra air switch for the brake controller so it would
only work when the brake was applied. The only other reason to disconnect the retarder is that
maybe the retarder could work while in cruise without taking it out of cruise. My Jake works that way.
Add a dash switch on the wire from main retard-relay mounted on dash 12v breaker panel in front of copilot chair to retard brake light relay. Or add the switch on this retard brake light relay's wire to air brake switches.
Our coach is different, as the air brake switches and retard brake light relay are mounted on front panel in street-side front compartment.
Switch is VERY handy to keep cruise control from turning off on highway dips when retard joystick is not in off position. Dip causes throttle to move to idle position allowing retard to come on, and at bottom of dip throttle will accelerate coach turning off retard, if cruise control is still active.
You are absolutely correct in wanting your trailer brake controller separated from your retarder application. There is two pressure operated pressure switches that work in parallel in the dash. By separating them and adding a heavy 12 diode they still can be redundant. Your retarder will be on one side and your brake pressure on the other. Take your brake controller trigger wire and retain on the brake pressure switch side, but isolated to the retarder brake application. Trailer brake controller activates every time the brake is applied as it should but is now isolated from the retarder application. Brake lights are still being illuminated with retarder use, but no trailer brake application. Step on the brakes and all works normal, retarder application and trailer controller. But controller has to be located at dash and one of the heavy spare wires used for trailer brake control. I changed to a now standard seven pin plug and also added a reverse light circuit , although I've never used yet. I totally agree with Barry and others about cruise control but have learned to just place retarder control to zero and leave retarder control on so will activate with brakes as needed
Scott
My 97 u320 cruise and retrader work together without disengaging the cruise. really slick operation. Common mod back then.
Most I've seen though disconnect the brake light function from the retarder. Bit more involved to allow retarder to activate brake lights yet not disconnect cruise and bypass trailer brake controller during retarder use. Yet still activate trailer brake controller with normal foot brake application. Disallowing trailer brake controller from operation of retarder resolves trailer or toad pad brake application. Much safer IMO
Scott
Would it make it less complex if I was ok with this functionality...
Cruise on
Retarder in manual mode (joystick used not auto retard)
When retarder activates NOT disengaging Cruise and brake lights not activated.
Was hoping that functionality would make it less complicated...like if I found the retarder relay that is associated with the brake light, just unplug it and the above criteria would be met.
Until I wrap my head around how it all is connected it's hard for me to grasp...and I'm in the desert and am hoping for a quick fix for the trip home. 👍
Pull relay and resolve later
Ok, but it seems there are multiple relays involving retarder/cruise/brake lights. Though there is one relay (R8) in my schematic labeled "retarder"...just thought if I disconnect that one the retarder won't work at all.
Why can't you just drive it home the way Foretravel designed it, then deal with it when you are home?
I could just use the retarder in auto mode and then wouldn't have to worry about smokin the trailer brakes in manual retard mode...just being cranky, want my cake and eat it too.
If your trailer brake controller is like most I've ever owned it's completely separate from the coach retarder/brake system. It uses its own circuitry to detect slowing and applies trailer brakes as needed. Has nothing to do with the coach stop lights being on.
Peace,
Don
I was looking though my wiring diagrams and I saw this and thought this might help.
Thanks Pete...I have that diagram also...it's just hard for me to figure out what relay to pull to do what I want. I'll have to just experiment until I figure it out.
Either do like DSD said or just add a separate brake switch for the brake controller. I always installed the diode and everything works great.