2018 Isuzu Mux wiring - brake controller and Van fridge


New Member
Mar 4, 2018
I would appreciate any help people can give me on this....

We've recently taken ownership of a 2018 Isuzu MUX - so far I'm very happy with the purchase

We are going to get a 17.58-3 in July/August of this year. I now need some advise on wiring of the MUX in preparation of getting the van.

Question 1 - I've been told that the '18 model Mux has a Variable Voltage Alternator fitted making the installation of an in line VSR from the tugs battery to pins 9 & 10 of the flat 12-pin plug of limited use when looking to power the van's fridge and hoping not to flatten the tugs battery. I'm thinking of fitting some kind of Ignition switched relay instead of the VSR to help - can someone please advise on how and if they would do it this way?

Question 2 - With Variable Voltage Alternators are there any problems with powering the van's fridge from voltage drop when on the move (via 12 pin plug) . The fridge we are installing in the van is the Thetford N504 - I've been told Variable Voltage alternator's output can sometimes drop to as low as 12v. I imagine by the time it reaches the van's fridge it will be significantly below this. Has anyone had any problems associated with this? Is there a DC-DC type charger I can fit in-line that will boost the voltage to an acceptable level or should I just install the thickest cabling possible to pins 9 & 10 and hope for the best?

Question 3 - I'm looking to fit my Tekonsha Primus IQ into the MUX to work the van's electric brakes. Are there any issues with using the Tekonsha along side a Variable Voltage Alternator?

Question 4 - Has someone installed a brake controller into a MUX recently and if so where did they tap into the brake light to enable the controller? I have the tow pack fitted in the MUX with related towing loom.

thanks again for any advise


Well-Known Member
Nov 7, 2013
Cooloola Coast, QLD
Most modern vehicles you get a towing harness to plug in for your 12 or 7 pin, less hassles, with your brake controller if you can't find the hidden blue wire which is the wire to connect your electric brake controller to, just run a wire to your 12/7 pin brake light may mean a few extra metres of cable though......no matter what the alternator don't connect up trailer pins or brakes the old way as the wires for the lights and brake switch don't go to the lights any more they just send a message to the BCU/ECU, with a towing harness this makes it all work and you can piggy back the connections from the socket if needed.......if this sounds confusing them go to an Auto Lecko.
Likes: Bluey
Jan 21, 2018
Shailer park
Redarc make a nice LV 40 amp dc charger or 25 amp model specifically designed for variable voltage alternators and you could mount one in the van next to the batts, car feeds redarc, redarc feeds batts with 40 amps and adjusts down as it's a smart charger, you could then run you fridge from van batts and get an relay or something similar like isolation switch for the fridge in the van to switch off when the redarc powers off when the car shuts off to protect the van batts or not worry about it and just be mindful that the fridge is drawing juice from batts when car is off no biggy for say hr or 2 stop as when you take off the redarc will replenish the batts very fast anyway.

Redarc have a great user free hotline you can call up and discuss your needs and situation/car/van etc, they can point you in the right direction then either wire it up yourself you go to one of their recommended installers/auto elec in your area.

Or, just run a dedicated Anderson lead from tug to fridge with at least 6 b&s cable via a ign relay in car. The cars altenator should keep the volts up enough once the fridge load connects and starts drawing from the tugs battery system and from front of car to fridge with this cable size or bigger you will only get half a volt drop or so and the fridge will still run fine at 11.5 volts anyway. Just that at the lower voltage the element might only be drawing 80-90% of rated amps but this should be bugger all in the performance of the fridge. If the volts gets down below 11 at the fridge then you might have issues.
I've always run my van fridge via a dedicated Anderson lead via the car and shut off relay over the diff vans I've had in the past as I recon it's the best way, and using heavy wire like minimum 6 b&s ( 13.5 mm) from car front to fridge is the go.

I rerouted my vans fridge wire as Jayco used 10 mm cheap looking cable and they ran it from fridge on awning side, up to door, then across to otherside .

I removed it, replaced it with 13.5 good aussie made cable, straight from fridge , up the same side to draw bar, saved me 2.5 mtrs distance for volt drop and materials, car has same cable from engine to rear.
I see only 0.5 volt drop from start to finish now and the 3 way fridge runs magic when traveling on DC now.
It's a large 23 amp rated dc element and when I plug my inline power meter in now I see 22.5 to 23 amps been used. So it's running to spec.
Big dc cables, go next size up if close or border line. Minimum 13.5 mm size, and don't let some auto elecs say that's over kill because many of these guys don't have a grasp on volt drop/amp ect especially on dc 12 volt high loads like fridges and distance to rear of van from front of car, it's a reason long trucks run 24 v systems etc , but you will be fine if you run big cable...
I got 10 mtrs of 13.5 mm square aussie made twin for $79 delivered on ebay.

Last edited:
Likes: Drover


New Member
Mar 4, 2018
Thanks again to Drover / Coldspace and DaveMC who assisted with my original info request; I've been busy following up on the information supplied and I'm starting to get a clearer picture in my head on what I require as far as getting my rig ready for the delivery of the van.