Thread: Electric Brakes How do they work?

Originally Posted by Lotz-A-Landies

Electric drum brakes don't work in reverse and the mechanisms are sided.

Not so for mine at least (ie working), although the linings are mounted to favour forwards direction. The lever swings in both directions, moving what is normally the trailing shoe instead of the leading one when reversing.

Originally Posted by weeds

Originally Posted by Lotz-A-Landies

I know that the portable Tekonsha Prodigy RF that can be used in any car without the car being wired are not legal in Australia because the manual over-ride does not illuminate the trailer stop lights as required by ADR.

so the P3 manual lever should make the brake lights come on?.......i must try that when i next connect the trailer

I don't think it will work on my D4 either because they had to add a diode to the brake signal wire to stop feedback from the D4 electronics.

I haven't fitted a diode to my D4 (yet) but no problems to date. I spotted today that using the manual lever with the ignition off only operates the van brake lights. I didn't check if the vehicle's lights operate using the lever with the ignition on but all lights work with the brake pedal with the igniton off. It was rego check time...

Originally Posted by Graeme

I haven't fitted a diode to my D4 (yet) but no problems to date. I spotted today that using the manual lever with the ignition off only operates the van brake lights. I didn't check if the vehicle's lights operate using the lever with the ignition on but all lights work with the brake pedal with the igniton off. It was rego check time...

Oh dear - late model landrover owners need to beware of ebc's - that dasterly red wire sensing the stoplight . - tekonsha have confirmed that when you use the manual lever - the tekonsha (p3 at least) sends current down the red wire to illuminate the brake lights. - yep that's all good in an old kingswood, but in modern cars with ecu's all over the place that's not good to have 12v current going backwards in the vehicle wiring.

My landy dealer is installing (on 2008 freelander 2) a diode protection 4 pin relay in the brake light wire that comes from the trailer ecu. the trailer ecu brakelight wire will pull the relay which will connect the constant 12v on the relay to the output, then the P3 red wire will be spliced in between the relay & the trailer socket. He said he normally does this at the brake pedal light switch but as i had someone else wire in the P3 (badly) and the wires are already run he is going to do it this way.


so the P3 still "senses" the brake light when brake pedal pushed, but when manual lever used on P3 all that can happen is current feeds through to trailer and cannot get back to ecu because relay is open.

a lot of auto elecs do not know this and will splice the wire in where they can. Installing the diode in the P3 red wire will make the installation not comply with ADR

He said stay well away from the cars stop light wires as they are controlled by fet's and it doesn't take much to upset them and they are not replaceable (IE whole new ecu required)

It seems to me that LR has on the D4 fully catered for the likes of the manual lever on the P3 to ensure the trailer/van brake lights illuminate as required by law and that the locally recommended diode is not required.

FETs are replaceable but obviously not by your local mechanic and that warranty would also be voided. FETs for power switching are high current and robust devices that usually also have an inbuilt protection diode that cater for the reverse polarity current produced by a coil (eg driving a relay) when its power is removed, not that a P3 would be expected to be operating a coil/relay using the sense wire circuit.

Hi Graeme

Not sure where the P3 was tapped in, I know that in the US there is a Tekonsha harness available to connect the P3 to the LR4 (D4).

I do know that the day after fitting the P3 I had a series of error codes, including special programs off, hand brake fail, esc off, hdc off etc etc, later that day the trailer brakes locked on and then a repeat if the full set of error codes.

Diana

I won't hazard a guess at the reason why one D4's P3 installation works fine without a diode yet another doesn't, only that I fitted mine so I know how mine's connected.

Edit: I wonder if your one was connected to a brake switch wire and that wire was not the one for the lights but for the failed switch check circuit.

Hi Graeme - just for my interest sake? have you used the manual lever on your P3 whilst driving?

i would expect that the cars electrics are robust enough to support the connection of these add ons - considering the intention of these cars to go off road and with the towing capabilities they are engineered with!