As part of the Katzkin group buy I ordered some heating units for my front seats recently. The instructions for putting these in say to wire them straight to the battery. This means that they could be on anytime - even without the key in the ignition. It would be just my luck to accidentally turn mine on when I was getting out of the truck some night and then wake up to a dead battery. I really wanted to have mine where they could only work when the truck was running.
I got a fair bit of help with this. See this thread:
As always - do this at your own risk. I am not a professional or an expert and have no business giving advice on complex subjects such as modifying your trucks electrical system.
First you have to install the heating elements. Check out the Katzkin install threads for full instructions on removing/reinstalling upholstery. I suspect most will add heat when you are already doing this part of the project.
The elements I got for my truck were pretty small. Hopefully theyíll be fine. They have a peel and stick type of adhesive and just stuck right to the foam of the seat. I cut a slit in the foam to route the wiring through.
I put the bottom heater under my butt. When I sit in my seats now, I think it would be better, if you only have one small element to put it under your thighs on the other part of the seat bottom. I didnít do this because I worried that the wire passing under the bar would cause problems. Iíll bet you could just run the wire directly through the foam to the bottom of the seat and avoid that all together. If it wasnít such a hassle to mess with this stuff Iíd probably change it. Oh well.
I ran the wiring harness for the R seat under the carpet to the area under the center console then to the L kick panel. The L harness went to the L kick panel as well.
To get them into the engine bay, I connected them together and ran one power and one ground wired out one of the rubber plugs under the drivers seat.
These pics were taken from when I ran other stuff through here - but I just ran these right with them.
You also have to find a wire that is ďhotĒ when the ignition is on and ďcoldĒ when itís not. This is the one I found that fits the bill:
It is the blue wire with the yellow stripe. I tapped into it with a wire tap and ran this with the rest of the heater harness to the engine bay.
All the wires were zip tied together and routed to the drivers side of the engine bay. At this point you could just run them to the Pos battery terminal and to ground, but If you want to have them controlled by the ignition you need to wire them through a relay.
This is a diagram of what I did:
I used this relay and relay socket:
The relay is necessary because it uses the ignition power to switch on power to the seat heaters. If ignition is off now power will reach the seat heaters - even if you flip the switches in the cab.
I mounted the relay through the hole in the top to one of the holes on the side of the engine bay. It turns out that the bolts that hold the jump seats in place for the Access cab fit these holes perfectly. I had to leave one of my seats out for a little while and tried the bolt here. If I can find a part number or something, Iíll post it - but the closest thing I could find at Home Depot didnít fit the threads.
Before installing you need to put a diode in the circuit. Apparently a relay wired like this can allow a spike of current back through your system. It is definitely above my head - but it was recommended to me that I put a diode between the white and blue wires. This allows current to flow in only one direction. Iím afraid if I try to explain my understanding of this someone who really knows what they are talking about will expose my ignorance. If you can explain this to others well - please post it here.
I used this diode:
You can see that it has a white line at one end - that end should be connected to the white wire. The other end is connected to the blue wire:
I put some clear shrink wrap over it all so I could still see what I had done if I forgot:
The relay socket has five contacts. The center is red and I just trimmed it short.
The remaining 5 wires connect as follows:
Black - Pos battery terminal (I put one of the fuse holders from my seat kit here)
Yellow - Red power wire from seat heater harness
White - to 12v ignition power (the wire I tapped into at the steering wheel)
Blue - Ground
The black (Ground) wire from seat heater harness goes directly to ground as well.
I need to get a little accessory fuse box, but until then I tried to zip tie everything in place neatly. Sorry for the poor pics:
Finally (and to me the best part) I installed the heater switches in the center console. If you remove the shift knob you can pop up the silver cover on the top of the console.
I drew out where I wanted the holes:
Then I used on of these drill bits to drill them:
I had to make the holes a little larger than the instructions said but they fit fine:
This is what it looks like underneath:
There are some friction clips to attach the cover very close to these spots. I had to use my dremel tool to clean them up so the switches fit OK.
Now it works just like I want. Heaters are disabled and will not work if the ignition isnít on. With the ignition on the heaters work perfectly:
The drivers side switch is on high, the passenger side is on low: