OLLIeCRX

While sitting browsing here earlier and seeing people always asking for the honda demister wiring / relays / switches etc I thought this might be of help to some people.

I spent a good while searching the forum and pieced together various odds and ends on how to do this but no definitive guide.. so hopefully this will help

I recently wired this in my MY99 JDM which has been retro fitted with what appears to be a genuine honda roof from an 06 car going by the info I had.

I have yet to wire the rear soft top screen, as I have had the hard top on all winter, but the principle is the same

***I AM NOT RESPONSIBLE FOR YOUR OWN INSTALLATION AND ANY DAMAGE CAUSED AS A RESULT OF FOLLOWING OF THIS GUIDE, THIS IS HOW I FITTED MINE AND I AM SIMPLY SHARING THE INFORMATION WITH PEOPLE***

You will need (all available in Halfords / Maplin / eBay / Motor Factors)

1x Illuminated Switch (your choice)
1x 4 or 5 pin 12v changeover relay

3m of cable, colour isnt massively important, I used RED (i used 12gauge, 10 or 12 should be fine)

Electrical Terminals - I used 7x insulated spade connectors for the relay terminals, and switch, then male/female connectors for the hardtop wiring release.

2 fuse holders, and 2 fuses (15amp)

Tools :

Voltmeter
Screw Driver
Wire Strippers
Wire Crimpers
Soldering Iron
Solder
Zip Ties


ok, I firstly fitted my switch in the blank below the speedo, just above where the keys go in (theres one in either side for various things, you can put the switch wherever you like)

The switch had 3 clearly marked terminals :

POWER IN
POWER OUT
EARTH

Using my voltmeter I tested the wires coming off the ignition barrel, and from memory the BLACK/YELLOW was the ignition source wire. I soldered a length of wire from this BLACK/YELLOW wire and connected it to the POWER IN on the switch. I inserted a fuse holder and 15amp fuse inline between the ignition wire and the switch for safety. I also took a length of wire from the EARTH terminal on the switch and put it to a chassis earth (drivers kick panel, or say at the radio wiring is fine)

From the POWER OUT Terminal i ran a length of wire to TERMINAL 86 of the 4 or 5 Pin RELAY, The opposite terminal, TERMINAL 85 was then also wired to a chassis earth (you can use the same earth as you used for the switch)

Essentially now the relay has a switchable power source, this can be tested by putting the ignition on and operating the switch, the relay should "click" when the switch is turned on and off, and also the LED on the switch should illuminate

Next you need to put your power source that will power the rear window to the relay. To do this I again measured the voltage on the WHITE wire at the ignition barrel, this wire is 12V CONSTANT and again I fitted and inline fuse holder with 15amp fuse in the length of wire between the WHITE wire and TERMINAL 87 on the 4 or 5 pin relay.

With this now connected this leaves TERMINAL 30 on the relay the only free terminal (ignore 87a if you bought a 5 pin relay). from this terminal you want to run a length of wire from the relay to the rear of the vehicle where the OEM rear window demister wiring would be. For me this is behind the passenger seat on a RHD car.

I removed the panel behind the passenger seat to allow me better access to run the cable.

My hard top has a grey 2 pin plug on a curly "phone" style cable which is clearly the wiring for the OEM demister.

I then carefully pulled off the plastic trim panel on the side of the hardtop, this revealed the black curly cable going up and one wire connecting to the rear window, and the 2nd wire connecting the to chassis of the hardtop.

The wire that is going to the window is what gets connected to the wire you have just ran from TERMINAL 30 of your relay, from memory this is BROWN, but please remove the panel to double check.

again from memory the remaining wire is BLACK and is to go to earth, I used a small section of wire and chassis earthed this to a screw behind the passenger seat panel, this then allows me to have both the 12v feed from the relay and the earth on connectors to remove the roof with ease.

Using the male / female terminals I then crimped each wire, this allows me to safely remove the wiring when I remove the hardtop.

Once complete build up, using ZIP TIES secure any cables and the relay, sit back and enjoy!

I will update this with pictures ASAP, I decided to do this off the cuff and have no pictures.

I`m not really one for leaving my rear window on all the time, I use it sparingly and always turn it off once it has sufficiently cleared.

I dont know what effect leaving it on constantly would have as the method I have devised is not thermostat or temperature controlled to cut off. I have been using this for several months now and its a complete godsend being able to see out the back of my car on cold mornings!!!!

I hope this helps people who are struggling with finding the OEM honda wiring, or who simply dont want to spend 3 fortunes.

And anyone please feel free to add to this, any additional info is more than welcomed

Madfish

Thanks for taking the time to do this

I'll be using this soon when I hook up my back window,

Mark

razzele

Great write up.

I may have to do this now i know how !

TommyS2000

Ive just installed my hardtop and my immobiliser is where the demister switch should go.
I didnt bother installing the demister and TBH im glad I didnt.
Once you are driving, open your window for 2 minutes and voila! No mist

nomadicS2k

Good work Ollie!

ian_6301

A jolly good "how to", Sir!

Well written, easy to follow and simple. Good plan.

Might I offer a suggestion or 3?

(For those with a penchant for difficult, massively over complicated plans, read on

1) For those who are not over-enamoured with the idea of soldering/splicing into ignition wires (I for one have no issues with it - you should see my landy...), you could always make use of the spare power terminals next to the fuse box:

https://www.s2ki.com/forums/index.php?showtopic=301506 (about halfway down page 1)

2) If you wanted a timer on your rear screen heater, this is fairly easy to do, as Maplin do something called a 555 monostable timer switch kit:

http://www.maplin.co.uk/555-monostab...tch-kit-220009

You have to build it yourself, but frankly, it's not rocket science and any eejit with a soldering iron and a steady(ish) hand should be able to manage it. After all, I made one!

If you wire up an ignition switched feed (via a fuse) and an earth to the "DC In" side of the module, a momentary push switch (placed as before) to the "TRG" terminals on the timer, a live feed (via a fuse) to the "COM" terminal on the relay in the module and the "NO" terminal to the window (as above), you can then adjust the potentiometer to give you a system that is on for anywhere between 1 second and 15 mins - Ideal!

The relay in there is rated for 24v 10A across the contacts, which *should* be good for the 12v 15A or so that we are dealing with. If in doubt, disconnect the wires to the relay terminals, add a wire from the + terminal on the DC In side to the "COM" terminal on the relay and then take a wire from the "NO" terminal to drive a standard 30A relay (as described by the OP), switching power from a fused live.

Depending on what else you have wired up, you may have room behind the dash for the module, or you may wish to stash it behind the panel behind the driver's seat - effectively on top of the fuel tank, near to the spare wheel. Either way, you'll want a project box to house it in. This range, or something similar would do:

http://www.maplin.co.uk/miniature-general-...51-series-43710

If you want to be able to know when it's on, instead of soldering in the LED, you could take a feed (2 wires) from there to somewhere near the switch and mount a seperate LED (looks nasty), or if you use an illuminated switch, just wire up the feed to that instead. Just to give you an idea, something like the switch at the link below is cheap and easy to come by, but you may want to go the whole hog and get a proper Honda switch to make it look more professional...

http://www.maplin.co.uk/illuminated-push-t...ke-switch-34861

The only downside with this setup is that once you push the trigger button, the heater is on for how ever long you set the timer for, come hell or high water. The only way that you will stop it is by turning off the ignition, which will de-energise the relay and shut off the live feed.

The alternative is to wire in a second switch or to use a DP/DT rocker switch that has a mom-off-mom action, where up would turn the system on (or restart the timer) and down would turn it off. However, that is probably a step to far, unless you are a real geek... ahem..

3) Fuses. 15A should be fine for the Live feed, but the switch and relay (or box of geekery) will not need anything like that much. Standard automotive relays use 0.15A and even if you use a hulking great 5w bulb in the switch, it'll only draw 0.41667A, making around 0.57A (or about 0.72A with the timer) so I'd suggest using a 2A fuse on the Ign feed.