Have you googled it, or looked on this site?
This is on FW

"I have a TowPro / Hydrastar setup, but...

Started out with a standard TowPro unit that wouldn't recognise the trailer.  Fixed the problem with a Load resistor, but the unit actively calibrates and wouldn't do that with a Hydrastar.  The solution was to calibrate on another trailer with a compatible unit, then it would be OK and it would work with the Hydrastar.  Unfortunately I didn't have access to another trailer.

Ended up buying the Elite version - changed the units over and it works fine.  The Elite calibrates differently and works well with my setup.

Like you, liked the in dash design of the TowPro.  Now have a standard TowPro for sale on Gumtree!!  Also have a P3 if anyone wants one."

Also on Hydrastar that some Redarcs are not comptible.

Check the blue wire at the Hydrastar, also check the earth is connecting between trailer/car

thanks mate
yeah google came up with everything where there is no power to the unit - I have power to the unit under brakes
I have been told that the towpro is compatible (but that remains to be seen!) and the blue wire that runs into the hydra star is getting 12v when the brakes are applied... just fitted the towpro and took me ages to get the controller in the right place..... ripper

hmm -looks like I will have Redarc towpro elite for sale shortly.....

It sounds like you have it covered already, but there is two 12V cables.

The first is on all the time, the 2nd is tbe beake signal. Need to make sure you have both of those.

Where are you testing for voltage at? make sure teh connnections on the trailer plug are all in good condition and making good contact through the plug.

Can't tell from your post but if you're stationary and trying the brake pedal, the tow pro won't work. Try pushing the red arc button manually, should hear the hydra star unit pump kick in. Tow pro elite works on inertia and won't actually apply brake if car is already stopped. Manually pressing button overrides this and energized brakes (handy when bleeding lines). Otherwise, when you first drive off brakes will be clunky until unit calibrates itself.

 I have a hydrastar unit and tow pro elite controller and it works great. Just get an auto sparky to have a look at it. Mine will work if stationary too, foot on brake unit kicks in. It's a new hydrastar and tow pro elite all installed early this year. 

 Just to throw it out there. Hydrastars have 2 circuits. If the breakaway works doesnt always mean the that the unit is fully functional. Theres afew tests you can do to verify the units running and wired up correctly. 

Once yourve verified the hydrastars fine then you can look at car.

If your near O'Conner, bring the trailer past fremantle trailers and we will have a look. 

 You do know that the redarc elite is a proportional controller right? As in it will only apply the brakes when it actually senses you decelerating, it does this so you don't burn out the actuator sitting at the lights. 

thanks all - so before I rip my dash out to remove it I might go for a run down the street - I did think if I turned it to manual and turned it up to 10 the unit would kick in... - test run tonight, no boat on the trailer so on manual and full braking (10) I should get lock up pretty quick....

Just to throw it out there - I have a Hydrastar but my controller is different. When I had the towball and seven pin plug fitted to the car the guy wired up the plug wrong. From memory the Hydrastar requires a pin with constant power. My guy wired this to the reversing light pin...so my unit only worked when I was in reverse. When I was Googling my issue  I did find wiring diagrams such as was originally done on mine...so perahps if they do not know you are planning to use it on electric brakes this may be the case??? 

i have a hydrastar unit but with a tekonsha p3 controller.. for the 7pin plug i had to get a auto sparky to allocate power to the reversing lights pin to ensure its constantly charging..

 Rather than using the reverse pin, I reckon its better to use an Anderson plug.
Can draw 20 plus amps and you can also use the anderson plug for other stuff when camping etc

Had the same issue, the unit won't calibrate with a hydraulic system. You need to calibrate it with a trailer with standard electric brakes first before you use it with boat trailer with electric/hydraulic brakes.

https://www.redarc.com.au/faq-tech-tips/tow-pro-elite-active-calibration

Hi pelagic my Hydrastar did the same the power cable to the plug was to thin as Resurgence explain. I used a 12v battery to test the actuator to make sure it work fine that is when I found that the thinner cable doesn't work  used a thicker cable from the 12v battery and the actuator work fine.

I took my car back to the auto electrian to fit a bigger cable came back and test with trailer and the hydrastar work fine but only in manual mode I struggle for days and the redarc towpro just refuse to go in auto mode. I send the towpro back and fit the towpro elite problem solved and the trailer brake works perfect. 

www.dunbier.com/wp-content/uploads/2013/05/HydraStar_SM.pdf

Go to page 8 and run the tests as described, if the resolution is unit needs repaired it is most likely the circuit board

I have 2 units with stuffed circuit boards, $200 for a new board or just get a brake commander and never worry about your brake controller or actuator again.

thanks guys
think the unit is ok - as westcoast suggested I tried it with car in reverse and it works fine -
does that mean I need to change the wiring though?

You know you are desperate when you take auto electrics advice from me!! I had never had electric brakes before. Assumed they were working as everytime I backed the trailer back they would lock up. Only took me a year to figure out nothing was happening under normal operation.  

Not sure where you are located but Russel from Advantec (mobile auto sparky) sorted it out. He is in the Scarborough area. Roland from Towsafe knows his stuff as well and will go through it over the phone...although I still needed a sparky!!

If you know a bit about electrics could probably do it yourself. From my limited knowledge the unit requires constant power, in addition to getting a signal when you press the brakes. Looks like the constant power wire is hooked up to the reversing pin...which is the way a lot of the wiring diagrams appear when you Google it?

My Hydrastar operates with a constant power supply wired to the reversing light pin (instead of a reversing light wire). Sounds like you need to disconnect the reversing light wire from the allocated pin on the plug and replace it with a 12 volt constant supply direct from the battery. If your unit works when in reverse, this seems to indicate that everthing operates when there is a power supply. I reckon this may solve your problem.

I was looking at compatability of my redarc controller and it is not compatible with the brake unit I am going to get.

Apparently it has to be progressive to work on a hydraulic setup...

 I have Hydrastar HBA-12 units on our boat trailer (with break-away) and camper trailer (without), but use Tekonsha controllers. After 8 years of tinkering this is how I set them up. Most has already been said above.

Large 7 pin plugs,  (7 pin small plugs cannot accept the required cable size). As Rob H says you could use an Anderson plug for Pin 2 & 3 if you already have one wired up. I dont because my anderson is running 50 A cct breakers and I prefer to run 20A on the hydrastar units.

Pin 2 (Reverse) Car Battery +ve to solid black on hydrastar, with auto reset cct breaker and at least 6mm auto wire.

Pin 3 (earth) Car battery -ve to hydrastar solid white (buy twin core for the above and use the black wire, large plug will also have room for the standard earth wire).

Pin 5 (service brakes) Controller signal wire to hydrastar solid blue.

There are also different generation hydrastar actuators and the controller compatability list changes depending on your units serial numbers. See hydrastar.com.au for all the info, but Red Arc does not crack a mention as its all US based. The Aussie distributor probably knows though.

oops