Redarc Tow Pro calibration in Disco 3

[Journeytower]

Hi Guys, I had a Redarc Tow Pro installed in my Disco 3 . The wiring was already in place from an existing brake controller I was not happy with . The Tow Pro had previously been installed in a TDI Disco I had, once I got to the top of a hill [smilebigeye]. Can't say I have a lot of confidence in the auto electrician that did the swap.

Problem is I can't get the Tow Pro to go into calibration mode & hence while the trailer brakes work effectively they are not as smooth in operation at the final slow down point.
When I go to put the unit in calibration mode as per the Redarc instructions with the ignition off , some of the dash lights come on as though the ignition was turned on. If I have the park brake on at the same time a Park Brake Error message comes up on the message panel when the ignition is turned on. This extinguishes when the ignition is turned off & back on again.

I have a feeling there is a feedback through the Redarc brake controller when trying to calibrate but I am unsure if this is a Redarc fault , a Disco fault or an installation error. Any suggestions out there as to the problem. Thanks, Wayne

[Tombie]

Check the wiring behind the tail light. Sounds like the diode may be incorrectly installed.

[LRD414]

Agree with Tombie but I also wonder about the brake wire connection. Is it incorrectly connected to the brake switch circuit instead of stop light circuit in the rear?

Scott

[Journeytower]

Thanks for the feedback guys.

An update, on my Disco the connections have been made under the dash except for the power supply coming direct from the battery via a self resetting circuit breaker & the blue service brake cable going direct to the trailer plug.

The Red signal wire of the brake controller was spliced into the Green with Purple trace wire at the brake light switch . This was done without a diode installed. As the green with purple trace wire does not have power supplied with the ignition off, when attempting to put the brake controller into calibration mode as per Redarc instructions with the ignition off the brake controller feeds power back into the vehicle ignition system & lights the dash lights . If attempting calibration outside Redarc instructions, that is with ignition on, there is neutral current flow due to 12 volt supplied to both side of the red signal wire & hence still no calibration mode for the brake controller.

I installed a three amp diode , as suggested on this forum so thanks again, in the brake controller signal wire, backed the car to the caravan & again attempted to enter calibration mode exactly as per Redarc instructions with the ignition off. Nothing happened, including no ignition lights came on, so on a winner there & a bit of a smile appearing.
I the turned the ignition on & went through the calibration procedure & voila the brake controller entered calibration mode, a bigger smile & reinforcement that if you want something done correctly do it yourself, mostly. The curse of an old mechanic.


I haven't tested the van on the road as yet but will over several days at the end of this week. I'll put in a brief report of or if any changes after correct calibration & mounting the controller securely.

[DiscoJeffster]

I’m sure it’s best to use the brake light signal from the rear loom and not the brake light switch. Read the sticky up the top of the forum.

[LRD414]

I’m sure it’s best to use the brake light signal from the rear loom and not the brake light switch. Read the sticky up the top of the forum.
Yes, there is a good reason not to use the brake light switch cable I just can't remember the detail.
Also, there was an update to the diode size. 3A can be too small depending on what lights the trailer/van has.
It's ok if installed only in a sense wire to controller but not if it's exposed to the full stop light circuit and there's more than 3A of lights.

Scott

[DiscoJeffster]

The diode is not in line with the power feed to the lights and is only part of a sense circuit to my recollection. It’s there to ensure the signal is one way only - to the brake controller, so as not to interfere with canbus sensing I believe? No current of any significance should flow through the diode as the brake controller only needs to sense a 12V signal. This is in parallel to the light circuit if wired correctly. It has been a while since I installed mine.

[LRD414]

The diode is not in line with the power feed to the lights and is only part of a sense circuit to my recollection. It’s there to ensure the signal is one way only - to the brake controller, so as not to interfere with canbus sensing I believe? No current of any significance should flow through the diode as the brake controller only needs to sense a 12V signal. This is in parallel to the light circuit if wired correctly. It has been a while since I installed mine.
That's not the only way to do it, hence my post.

Scott

[DiscoJeffster]

I may recall wrong and if so I apologise.

[LRD414]

Not wrong, just two options. Refer post #450 on page 45 of the D4 EBC sticky thread.
D4 Electric Trailer Brake Wiring (https://www.aulro.com/afvb/l319-discovery-3-and-4-a/97935-d4-electric-trailer-brake-wiring-45.html)

The diode needs to be upstream (CJB side) of the splice if you want the TowPro manual override button to illuminate the trailer brake lights. If that is not required then the diode can be located in the sense wire. Note that the 3A diode size only suits the sense wire position and needs to be larger if more current will flow to the trailer stop lights and its located in the stop light cable.

Scott

[Tombie]

The diode is there to prevent the CJB being cooked if a spike or short occurs...