I have just purchased a 2017 Isuzu Dmax Tour mate and thought I might explain how to access the engine bay from the cab interior without wrecking the vehicle and setting off the airbag,This is my 3rd Dmax so have explored various options ,this has proved to be the easiest yet.

Before starting a couple of things to note,The 2017 Dmax is equipped with a smart alternator,wiring of Red arc and Cteck 250s (Silver and Black models)devices need to be explored on their various websites for wiring diagrams.I use a silver Ceteck 250S dual for charging my Caravan batteries,up graded wiring is necessary using simple 30 amp automotive relay ,easily installed if your Dmax has a smart Alternator .Google up Cteck 250 250S dual and smart alternator its all there to see.Unfortunately I dont know about the Redarc unit so cant comment ,I'm sure there is something about it on line.

Accessing engine bay from cab for wiring .

Looking into engine bay from front of vehicle on LHS of motor directly behind the turbo unit and to the upper right of where steering rod comes through fire wall is a diamond shaped plate about 75 mm high and about 50 mm wide,this is where we are bringing the wiring through from the cabin.The plate is bolted through the firewall and two 12 mm headed nuts need to be removed from the cab side,carefully remove the two nuts making sure they dont drop down behind the floor matting impossible to retrieve unless all the matting is removed (I know)had to find a new one .Nuts removed ,the plate is stuck to the firewall with a rubber gasket,getting down under the driver side dash I used a wooden broom handle and hammer to drive the plate free into the engine bay.

Modifying the plate.

Retrieve the plate,I drilled a 18 mm hole through the centre of the plate and silicon-ed a piece of agriculture PVC pipe into the hole about 25 mm each side of plate,smaller pipe or other devices could be used to protect wiring from chafing on the plate reinstall the plate with a gasket of silicone to the firewall (replaces the rubber seal probably damaged on removal). I used 18-19 pipe as I intend to silicone the wiring inside the pipe to prevent water ,dust and fumes entering the cab when all wiring complete.

Picking up a Ignition switched power without doing too much damage in the Cab.

I decided to pick up my switched ignition power off the cigarette outlet in the top glove box .To access the wiring off this outlet ,open the lower glove compartment,grasp each side with your thumbs inside the box gently pull the whole glove box upwards it has two plastic clips on the bottom a fixing it to a hinge,a bit of strength is required when it comes off the hinge,remove the G/box.

Behind where the glove box is a plastic plate with 4 securing screws 3 recessed across the top the 4th is located about the centre of the plate in front of you.This plate is integral part of the glove surround ,it pulls outwards towards the rear of the cab and has plastic knife like clips on the top and bottom of the sides ,gentle pull and work the plate/surround out ,the clips will release ,make sure you pull backwards so as not to damage these clips,its a bit of a fiddle ,dont be in a hurry,when Plate /surround is removed access to the cigarette lighter is easily seen.pulling the plug off the lighter is a another story, I didn't work it out .

Connection to the wiring behind lighter was achieved by splicing into Yellow/brown positive side 12 Volt ,single black is negative.I used crush connectors and red black 3 mm twin flat its rated at 10 amps same as the cigarette lighter for my switching leads ,I ran two of these as its easy to pick up the second one at a later date if needed ,than doing the G/box removal. insulate your splicing and feed your wiring across the transmission hump to the drivers side and into the engine bay via your pipe though firewall.I used a couple of zip ties to secure the wiring from moving around. carefully Replace glove box  .Hey your done !

Think about installing CB Antenna ,Power cable,electric brake wiring through the Ag pipe /plate before sealing up with silicone.Use split loom to cover all wiring in engine bay and keep wiring as far as possible from turbo maybe some heat shield wouldn't go astray over wiring in this vicinity 

Points to remember make sure ignition is off and keys removed before cutting into wiring behind lighter.if your not completing your other wiring straight away insulate the ends with tape so they dont short out when next you turn on the ignition .Dont want to have to replace fuses for being slack

Cheers Philby