I have two seat heater diagrams side-by-side. These are 12V car seat heater diagrams and I wanted some help understanding the difference between the two and the left would activate and heat up vs the right. Both seats have the Ignition, Ground, TH and SW connections. The SW connection if i'm not mistaken goes to some relay but there is 1 connection that is only on the left side and thats the P connection.

I just wanted to try and figure out how i can make the left one work and heat up based on the right one's wiring. I have in place the wiring from the right hand side diagram but I have the heated seat system of the left side which I cannot activate without the P connection.

Any help or advice would be great.

Thanks

 

The fact that some of the names of the Inputs/Outputs are similar, means absolutely nothing.

The Seat-Heaters are controlled by the "Body-Computer" of the Car.

See those "Black-Boxes" labeled "Seat-Heater-Control" ?,
Those must be removed and replaced by a Custom-Thermostatic-Control-Circuit
if You expect the Heaters to function safely.

That is, unless You can find specific and detailed information and specifications for the
types of signals the manufacturer used,
and exactly what they do, and why they designed it that way.

The likelihood that You will ever find this information is "slim to none".
The manufacturers Electrical-Troubleshooting-Manual "may" provide enough information
to estimate the functions of the Inputs and Outputs,
well enough to get the System to have limited functionality.
The manufacturers Electrical-Troubleshooting-Manual is absurdly expensive,
usually in the ~$300.oo range, that is, if You can get one.
Some manufacturers will not sell them to the public.
.
.
.

 

The fact that some of the names of the Inputs/Outputs are similar, means absolutely nothing.

The Seat-Heaters are controlled by the "Body-Computer" of the Car.

See those "Black-Boxes" labeled "Seat-Heater-Control" ?,
Those must be removed and replaced by a Custom-Thermostatic-Control-Circuit
if You expect the Heaters to function safely.

That is, unless You can find specific and detailed information and specifications for the
types of signals the manufacturer used,
and exactly what they do, and why they designed it that way.

The likelihood that You will ever find this information is "slim to none".
The manufacturers Electrical-Troubleshooting-Manual "may" provide enough information
to estimate the functions of the Inputs and Outputs,
well enough to get the System to have limited functionality.
The manufacturers Electrical-Troubleshooting-Manual is absurdly expensive,
usually in the ~$300.oo range, that is, if You can get one.
Some manufacturers will not sell them to the public.
.
.
.

I've had a look into it further by accessing paid section on the manufacturers tech portal. And on both seats the
SW goes to the Seat Heater Switch and TH goes to Relay on the Seat Heater Switch The only thing I cant find is the P

 

See those "Black-Boxes" labeled "Seat-Heater-Control" ?,
Those must be removed and replaced by a Custom-Thermostatic-Control-Circuit
if You expect the Heaters to function safely.

OK So I think I figured out a solution. Transfer the Seat-Heater-Control which seems to be a small electronic box under the seat. So the Seat-Heater-Control box is a tiny box that looks like a relay. On the left diagram seat the control box has 5 wires and on the right it has 4.

 

P is possibly "Positive", ie. 12VDC. The thermistor is a resistor that has a resistance that varies with temperature. It works by being in series with a fixed resistor. A current is passed through the two serial resistors, one varying and one fixed, and the voltage where they join is proportional to temperature. The problem with the circuit diagrammed on the left is that it shows no functional link between the thermistor and the SW. Of course there is one, but it's black box and probably handled inside the BCM.

 

ok so i compared both seats physically and checked the wires. I'll refer to the seats in the diagram as left and right (left being the newer one with the 5 wires and the right being the older seat with the 4 wires which i have connections for)

Both the seats have 4 wires going from a small black box called the Seat Heater Control Assembly which is mounted under the seat very close to the main connector. This box looks a bit like a relay of some kind. The right seat has 4 wires coming from the main connector via a disconnectable plug to this black box and then from the black box there is a 4pin connector with 4 wires going to the seat heating elements.

On the left seat, there is also a identical 4pin connector that goes from this blackbox to the heating elements of the seats. However, the difference is this blackbox does not have the 5 wires coming from the main connector to a seperate input connector. Instead, the 5 wires related to the seat heating seem to come from the main connector and go inside a black conduit, wrapped in a lot of insulation tape and then it's somehow linked to this same 4 pin connector that is the output to the heater elements. But it appears there is only 2 wires going to the seating element itself. Whereas on the right seat, there is 4 wires going to the seating element system.

On the left diagram, that zigzag component between TH and P seems like it's incorporated into the wiring loom and taped up because it doesnt actually go to the blackbox like it does on the right side seat. What is that zigzag component? and how does it differ from it's function on the right seat?

So, what i'm trying to figure out is how to adapt it so I can transfer the blackbox over from the right seat to work on the left seat so that the cars original 4 wired control is able to operate the seat heaters.

 

The zigzag indicates a resistor and in this case a thermistor. It has to be placed in the seat near the heating element, not in the loom. Unless someone modified it.

What vehicle is this? You should be able to find very specific information. It's not always easy, but the information should be out there.

 

OK, so I did some more digging and physically tracing the wires on both seats. So on both seats it appears there are only two wires (red and black) that actually go to the heating elements of the seats from the black box.

On the right seat. There is two additional wires from the black box going to what appears to be an embedded thermistor in the seat itself. So that thermistor provides the feedback back to the black box itself. On this same seat there are 4 wires coming from the car loom. 1 is ignition from battery via 15a fuse. 2 is ground. And the other two come directly from the seat heater switch unit itself. This is a switch on the centre console.

The other seat on the left works very similar in that there are two wires (red and black) going to the heating element. But where it is different is that the thermistor which is also integrated into the seat does not directly feedback to the black box on this seat. Instead the thermistor is connected back to the heater control switch on the centre console. Therefore the difference between the two is that the right seat uses the black box to regulate the temperature based on the feedback it receives from the thermistor. Whereas on the other seat, the regulation seems to be happening directly from the heater switch itself. It explains why the two blackboxes are slightly different size. The one that’s doing the regulating is big and the other is very small.

Based on this. I’ve modified the drawing attached below with the proposal to transfer over the. Black box from the right seat to the left seat and connect the thermistor to that black box.

If anyone can kindly have a look at the diagram I’ve drawn below. Does it look right?

Also, are thermistors polarity sensitive? Because I would need to figure out which way round to connect the two thermistor wires to the old black box

Also, not sure what the dotted line on the thermistor is on the right seat

Thanks

 

Also, are thermistors polarity sensitive?

No, they're not. They're special resistors that, instead of being as immune as possible to temperature like a normal resistor, are designed to change resistance with temperature.