Hello all,

I have a MK7 Fiesta 1.0 EcoBoost with ST seats. The ST seats are heated and I am trying to make them work.

My car does not have the loom with the connector at the passenger footwell, nor does it have the fuses already in place on the fuse box. My ZS seat connectors are 7-pin like the ST seats.

I have the heated seat switch, smaller switch loom (that would have been connected to the passenger side connector) and the heated seats.

I know that the ST heated seats use the black, brown and blue connectors.

I have the wiring diagram / schematics for ST seats (see picture - thanks Unofix) and am comfortable with adding cables from the seat switch loom to the heated seats.

As I do not have the fuses I don’t think the wiring is in place on the fuse box so think I would need to tap into an ignition live. This is the part I am not sure on.

Would I need to tap into an ignition-live cable that is fused at 15a or more at the fuse box? If so, would I then run two cables from this ignition-live to each of the heated seats with an inline 15a fuse on each cable?

Just not 100% sure if I should be following the ST diagram as it’s retrofit so unsure if it needs to be done differently in my car?

However…

I was sent a (very skewered) guide of another way to do it but I’m not confident it’s right. I’ve added a photo of my breakdown of this too, excuse the writing. This shows the seat colour terminals their wires as well as the suggested wired the guide says. This guide suggests two cables go to the same switched green (high indicator?) and switch colours blue/black (to ground) and blue/brown (also to the permanent live).

Can anyone give some advice?

I would like the sense of satisfaction that I’ve managed to install myself (with some friendly help, of course), which is why I’m trying myself.

Thanks in anticipation.

(All of the other guides I have seen are where the loom cable already exists or aftermarket seat heaters are used).

I'm not familiar with a later Fiesta, but I would use a relay with the contacts supplied off a permanent supply to feed the heating pads, and the coil from a ignition switched source.

Thanks for your reply.

Are you suggesting that I wire it up like the ST diagram above but change the incoming power feed from the fusebox to a permanent live with a relay? Would this be 1 permanent live looped to connect both seats, or 2 separate permanent lives, one for each seat?

Also what do you mean by coil - I can’t see reference to that on the diagram? Is the coil not part of the heating pad?

Relays are normally four terminal devices.  Two terminals for the relay coil, and two for the relay contacts that switch on the current for whatever load is to be supplied.  The relay coil uses a low current source, and when the relay coil is energised, it enables the much higher load current to pass through the switching contacts.  Often used for headlights, horns etc..

The relay coil needs to be fed from an ignition controlled supply, and the switching contacts from a permanent high current source using suitable cable for whatever the maximum load of the heating elements, protected by a fuse of suitable rating.  You could feed both seats from one relay.  Like your car, my 2007 Fiesta has empty fuseways and no wiring for the heated seats, to which I was fitting the comprehensive X-Vision kit, which came with 16 pages of instructions.  But there was a connection from a 60A fuse way from the battery, to which I connected a 15A fuse to supply the relay contacts which were switched by an ignition supply.  This fed both seats.

You would not feed two 15A fused loads from one 15A fuse, as this does not give you any discrimination.

I do not have a Haynes manual for a 2016 car, but it may well have a much clearer diagram for the heated seats.

https://www.swe-check.com.au/editorials/understanding_relays.php

Perhaps you should seek advice from an auto-electrician.

Thank you for your reply Paul, very helpful.

You mention the relay coil needs to be from an ignition live and the switch contacts from a permanent live. Shouldn’t this be the other way around?

Would it not be that the relay is always ready to send power to the seats via a permanent live and the switch completes the relay-circuit via an ignition live (when the button is pressed)?

I think I’m slowly getting there!

How I did it on a 2007 Fiesta.

30 - Battery +ve

15 - from Ignition switch feeds K79 Ignition switch relay, pins 1 & 2 are the coil. Pins 3 & 5 are the contacts.

So when ignition is on, energises the additional relay to feed HFS

 

Thanks for that Paul.

Would it be better to use a 30A or 40A relay? Both seats have one 15A fuse each when installed from factory.

I understand I’ll need a fuse between the battery +ve and relay - am I right in thinking this needs to be 30A minimum? (To match the 2x 15A seats) therefore limiting the current to the relay to 30A anyways?

At what point would I need to include a 15A fuse to protect the seats? Would this be on the ‘feed’ line coming out the relay to the seats? If so, would each seat need its own 15A in-line fuse?

I wouldn't ask me ! My kettle has just gone Bang! With a big blue Flash !

I don't feel able to answer that specifically, I do not know the load current.

The starter is the maximum full load current, this determines the current carrying capacity of the supply cable.  The supply fuse rating is then set to protect the supply cabling to that load.  If you have fuses in series, and loads in parallel then you need to discriminate, so that a single fault does not take out the supply fuse to other equipment fed from the same source.

The X-Vision Kit to which I referred earlier came with a 15A Fuse, but if you have a Haynes with circuit diagrams, then I would refer to that.

22 hours ago, JJMS said:

At what point would I need to include a 15A fuse to protect the seats? Would this be on the ‘feed’ line coming out the relay to the seats? If so, would each seat need its own 15A in-line fuse?

Each seat will need it's own 15A fuse. Normal practice would be to install the fuse before the relay, then if it should ever go faulty the fuse will blow. Just make sure you fit the fuse in the main supply wire to the relay and not the relay coil terminal.

Thanks both. I will give this a go at the weekend.

I did stumble across the ‘add-a-fuse’ connectors yesterday and was wondering if either of you had any experience with these?

My thoughts are that one way of wiring in these heated seats would be to piggyback off of a 15a fuse already in the fuse box. With the add on fuse, both the original circuit and new circuit would be protected by their own 15a fuse - of course it would be 1x seat per piggybacked fuse.

I have been advised that the power draw for a single seat is about 5-6a (which makes me wonder why they’re protected by a 15a fuse and not a 10?)

Any reason why this approach wouldn’t work?

Piggy Backs - remember to put them in the "correct" way, ie with the common end of the piggy back connecting to the busbar side of the existing fuseway.  That way each load is protected by it's own fuse.

If inserted the other way, the combined load is taken by the first fuse, then the load is split back into the fuse box, and your new load.

The fuse is to protect the wiring, and although the standing load may be about 6A, I have no idea what the inrush current is into a cold heating pad.  Do the switches turn off the seats after a set time period ?