That’s right, this unicorn feature can be yours – if you’re lucky. Rear heated seats were a very rare option in the 93-00 run of P80 chassis Volvos. They were available in the 850, V70, V70 XC, and S70 models. It’s nothing short of sublime having a heated torso in the Winter, and extending that pleasure to your backseat passengers is a treat they will surely love.
A junkyard is your best bet
There are a few caveats to this, as locating the parts is often the most difficult part. I’d rate the install a 5/10 for ease, but 8/10 for actually finding the stuff. A junkyard is your best bet, as once in a while one of these super rare vehicles will pop up. I’ve seen this feature in a few different vehicles, like a ’98 V70 XC, ’98 S70 GLT, and a ’98 V70 GLT. Still haven’t seen a ’99 or ’00 with this option installed – but they’re out there. More on that later.
The 850 used a different system that allowed independent heater control of each rear seat. From what I gather, it may have only been available for 850s ordered through Volvo’s overseas Tourist and Diplomat Sales channels, and not as an official option stateside. In short, there aren’t that many.
The fallopian harness
Know your pads
The 98-00 rear heated seat system is controlled by a single switch in the center console. When pressed, a timer-relay activates for 15 minutes and heats both rear seats, bottom and back. That’s more than you get in a new Kia Optima, which only heats the seat bottoms in the rear. (Can you say cost-cutting?) Thus, the Volvo S70 is a clear winner in any comparison test.
The heating pads are wired in series, with the chain ending at a ground bolt under the driver’s side rear cushion. The whole seat system is fed by a single 12v wire that comes from the center console. This means that if one pad fails, (even a minuscule section of heating element) the entire system is rendered useless. There is also thermostat in each seat bottom pad that will cut power to the system if they get too hot. The system really is quite simple, and I like how Volvo designed it without utilizing a mass of wires to implement it. Every car was built with holes for the wiring harness clips in the body, and the seat pads have holes pre-cut for each pad’s wires.
Console wiring
What’s the heart of the system? The center console. The only difference between a car equipped with rear heated seats and a car without them is the center console wiring harness. Every car’s body harness already has the wiring in place to power this system, but it is dependent on the console’s harness whether or not it gets utilized.
Normally, the rear seat ashtray panel only houses a 12v socket. As our coddled bottoms know, cars with rear heated seats also house the momentary control switch in this panel. This switch toggles the orange relay, which shoots power out to the rear pads for 15 minutes. Rear heated seats cannot be “left on” because the driver has no control over them. Hence, the reason for a timer relay.
The best part about this harness is that it simply screws in to your existing center console, with no modification needed. It can be retrofitted in five minutes… if you have a ’98.
Console harness receptacles
Getting it to work in a ’99-’00
There are three connectors on the console harness that meet under the parking brake handle. One is the OBD-II port wiring. The other is the yellow, switched 12V source for the rear heated seats. The third is the larger main connector for the console’s 12V cigarette lighter outlets and front heated seat switches. This connector differs greatly between ’98 and ’99-’00 vehicles. Luckily, the wire colors remained the same between years and a ’98 console harness with rear heated seat functionality can easily be retrofitted into a later model vehicle. I did this on my ’99, and it worked flawlessly.
There’s a few ways to convert a ’98 style plug to the later version. You can simply de-pin the wires out of the ’98 connector, and insert them into the correct slots on a ’99 connector. (Use my pictures as a guide) Or, you can cut the wires and splice them. Obviously it’s a bit more time consuming to de-pin the connector, but it looks a lot cleaner all said and done. (Ignore the butt connector in my ’99 wiring, I screwed up) And of course, it’s as easy as reversing this process to install a ’99-’00 console harness into a ’98 vehicle.
Wire up the rear
Installing the “fallopian harness” is as easy as popping the clips into their designated holes on the body. You can’t screw this up. The yellow tail of it goes down the passenger side of the tunnel under the carpet, past the console, and snakes up in front of the shifter. It then loops back to the OBD-II and console harness connectors. In the rear, it branches and goes to each side of the car under the seat cushion, just peel back the carpet a little.
Install the pads
If you like upholstery work, you’ll love this. It’s just enough work to get a taste of what it’s like to work in a seat factory, but not so much that you’ll never want to do it again. The worst part was removing the entire rear seat – yep, the seatback and bottom need to come out for this step.
As far as getting the heating pads, you’ll need to either install a set of rear seats with the feature already installed, or gently cut the leather in a junkyard car to peel the heating pads off of the foam. They are glued from the factory, but not hard to remove at all.
NOTE: V70 seat bottom pads have much longer wires than S70 bottom pads. S70 bottom pads will need their wiring extended for use in a V70/V70XC as these vehicles utilize hinged seat bottoms.
Once your seats are out, the hog rings can be removed with a pair of pliers and you can unzip the upholstery where applicable. The pads are easy to align – they match the seat’s pad design perfectly. Use a spray contact adhesive on the foam and slap the pads down. Run the wire through the existing holes in the fabric, zip tie (or hog ring if you’ve got the tools) it back together, and you’re done.
Even though it’s warm outside, keep an eye out for these kits at the junkyard. The parts aren’t available from Volvo anymore, so it’s a dwindling secondhand supply. Having this feature is a cool trick that your passengers definitely won’t expect, and will get a lot of use if you frequently cart people around.
A Complete Rear Heated Seat System
About the Author: Alex Fiehl
Alex is FCP’s Blog Manager and an automotive enthusiast based in Endwell, NY. He has over 8 years of experience working on a wide array of import makes, but is partial to Volvo and Subaru. In his free time he likes to write about cars and drive his two Volvos.