Sanky Posted March 18 Author Report Share Posted March 18 The control unit is part of the under seat heated wiring loom. Looks like a relay, but has Pic inside with some other electronics to monitor the temps. Quote Link to comment Share on other sites More sharing options...
½cwt Posted March 18 Report Share Posted March 18 So if paired with the correct original switch and the correct wiring it should switch power modes I'd have thought. You can't just plug in 12v and hope it will work correctly. The wiring diagram gives you the pin outs for the switch, the control unit and the connector under the seat at least. Quote Link to comment Share on other sites More sharing options...
Sanky Posted March 18 Author Report Share Posted March 18 50 minutes ago, ½cwt said: So if paired with the correct original switch and the correct wiring it should switch power modes I'd have thought. You can't just plug in 12v and hope it will work correctly. The wiring diagram gives you the pin outs for the switch, the control unit and the connector under the seat at least. Not sure what you are getting at. But I’ve done the complete wiring from the switch to the seat as per the factory wiring. The switch is functioning as it should, press once for high, press again for low. Press the led on the switch to switch off. I just don’t feel the seats heat up as much I was expecting. I have not fitted eBay heated seat elements to factory switches. Quote Link to comment Share on other sites More sharing options...
iborguk Posted March 18 Report Share Posted March 18 (edited) 1 hour ago, Sanky said: The control unit is part of the under seat heated wiring loom. Looks like a relay, but has Pic inside with some other electronics to monitor the temps. Would have thought on that basis the live values for temp should be readable by the right gear. I guess sit in another 986 owner's car nearby and see if they are the same. Edited March 18 by iborguk Quote Link to comment Share on other sites More sharing options...
½cwt Posted March 18 Report Share Posted March 18 2 hours ago, Sanky said: Not sure what you are getting at. But I’ve done the complete wiring from the switch to the seat as per the factory wiring. The switch is functioning as it should, press once for high, press again for low. Press the led on the switch to switch off. I just don’t feel the seats heat up as much I was expecting. I have not fitted eBay heated seat elements to factory switches. It was confirming info for others, not critique for your work. Someone seemed to be suggestion just connect 12v through the switch and to the seat, but it needs a more rigorous approach as you have demonstrated. Quote Link to comment Share on other sites More sharing options...
TV8 Posted March 19 Report Share Posted March 19 14 hours ago, Sanky said: The control unit is part of the under seat heated wiring loom. Looks like a relay, but has Pic inside with some other electronics to monitor the temps. You mentioned the seats have a resistance of 0.8 ohm. My 987 seats have a resistance of 1.3 ohm. Using the law of ohm V=IR. Assuming V is 12v and as we have different resistances, we would see different currents in the circuit for our respective seats. Assuming the seat resistance is fixed (my seats have two terminals), the current has to be controlled somehow and must be also measurable at the output of the control unit? With the two settings on the switch, I would be looking for a difference between settings and if possible, absolute values for each with the ammeter in series to the circuit for the current. Quote Link to comment Share on other sites More sharing options...
Sanky Posted March 19 Author Report Share Posted March 19 3 hours ago, TV8 said: You mentioned the seats have a resistance of 0.8 ohm. My 987 seats have a resistance of 1.3 ohm. Using the law of ohm V=IR. Assuming V is 12v and as we have different resistances, we would see different currents in the circuit for our respective seats. Assuming the seat resistance is fixed (my seats have two terminals), the current has to be controlled somehow and must be also measurable at the output of the control unit? With the two settings on the switch, I would be looking for a difference between settings and if possible, absolute values for each with the ammeter in series to the circuit for the current. 0.8 Ohm is for each heating element, base and back. These are wired in series giving a total resistance of 1.6 Ohm per seat, so not far off from you have. When the seat heater is turned on one seat only, its drawing around 5.8A per seat. It makes no difference to the current drawn if the seat heaters are set to High or Low. The only difference for the temperature setting, is that control unit under the seat switches the power on and off to the heating element sooner for the lower temp setting. So must have built in thermoset in the control unit to monitor the temperature. Some calculations below using ohms law. Current drawn 5.8A, Heating Element Resistance 1.6Ohm, Voltage 13.5 5.8A x 1.6Ohm = 9.28V across the heating elements. 5.8A x 9.28V = 53w for the heating elements, which seem correct on google for heated seats in general. I took some readings with infrared thermometer, on High setting I get a temperature fluctuating between 22C and 19C. On the Low setting its around 16C and 14C. I think this concludes the seat heaters are working correctly and I just trying to compare older technology in the Porsche to my newer technology in the Jaguar. But if someone can share some temperature reading with a similar device, it would be appreciated. 2 Quote Link to comment Share on other sites More sharing options...
TV8 Posted March 19 Report Share Posted March 19 6 hours ago, Sanky said: 0.8 Ohm is for each heating element, base and back Do you have 4 heater connection terminals with 2 on the base and on the back? I only have two, at least as far I can see? Anyway, it seems like they are working correctly although not sure what sort of thermostat would be fitted. Timer maybe? When I was thinking about this earlier, I was expecting there to be a variable resistance added to change the load and you have a constant load. I was expecting a higher wattage and if it was 55w, that is exactly the rating of a headlight bulb. I would be trying the two settings on a bulb to see what happens! Good luck Quote Link to comment Share on other sites More sharing options...
Sanky Posted March 20 Author Report Share Posted March 20 11 hours ago, TV8 said: Do you have 4 heater connection terminals with 2 on the base and on the back? I only have two, at least as far I can see? Anyway, it seems like they are working correctly although not sure what sort of thermostat would be fitted. Timer maybe? When I was thinking about this earlier, I was expecting there to be a variable resistance added to change the load and you have a constant load. I was expecting a higher wattage and if it was 55w, that is exactly the rating of a headlight bulb. I would be trying the two settings on a bulb to see what happens! Good luck @TV8, on the 986 seats you are correct there are 4 heater connections, 2 for the base and 2 for the backrest. Then I mentioned thermostat earlier, its probably not the correct terminology and more like a thermistor built into the CU that measure the temperature. Are you trying to fit 987 heated seats into a 986? I think you should be able to do this quite easily if you were to use the 986 CU, switches and wiring. You may want to start another thread if you are serious about getting the 987 heated working in a 986, as others may benefit from the details. Quote Link to comment Share on other sites More sharing options...
TV8 Posted March 20 Report Share Posted March 20 2 hours ago, Sanky said: @TV8, on the 986 seats you are correct there are 4 heater connections, 2 for the base and 2 for the backrest. Every day is a school day! Thank you. 2 hours ago, Sanky said: Are you trying to fit 987 heated seats into a 986? I think you should be able to do this quite easily if you were to use the 986 CU, switches and wiring. Did you have the parts details you used here please? It sounds like the output would be on 4 heaters and the 987 seats only have a single connector. 2 hours ago, Sanky said: You may want to start another thread if you are serious about getting the 987 heated working in a 986, as others may benefit from the details. it started with another question but hopefully covers it - Quote Link to comment Share on other sites More sharing options...
Sanky Posted March 20 Author Report Share Posted March 20 Parts list, apart from the heated seats. 2 x Seat Heater SW 986 613 152 10 A05 1 x Fuse Box Terminals 000979227E 1 x Plug Socket Left White 999 650 109 40 1 x Plug Socket Right Black 999 650 035 40 10 x Connectors for plugs 999 650 330 00 1 x Contact Pin Bush for BS connector 999 650 320 22 1 x Female Contact Bush 999 652 568 22 Wiring loom as per wiring and routing of your choice, I followed the factory wiring loom best I could. @TV8, the 986 seats don't have 4 heating elements built into them, there are just 2 heating elements wired in series that end up with 2 wires going to the CU unit. Hope that makes sense. 2 Quote Link to comment Share on other sites More sharing options...
K.I.T.T. Posted March 21 Report Share Posted March 21 Informative thread @Sanky 👍 A quick question about this: On 3/18/2024 at 4:08 PM, Sanky said: I had to replace the heated element for the back rest for a new, when I measured the resistance on the new element it was around 0.8 Ohm. Where did you measure this? My driver's seat heating died a while ago, and it's on my list of things to eventually investigate / rectify. If the button's pressed, it momentarily lights up red, before extinguishing. Guessing it's either a bad element, or control unit. Do you have any advice on diagnosis? If it's an element, what's the easiest way to determine whether it's the base or backrest, or do you have to start taking the seat apart? Quote Link to comment Share on other sites More sharing options...
TV8 Posted March 21 Report Share Posted March 21 On 3/20/2024 at 11:54 AM, Sanky said: there are just 2 heating elements wired in series that end up with 2 wires going to the CU unit. Hope that makes sense. Thinking about this, doesn't connecting the elements in series increase the resistance compared with in parallel if connecting 4 down to 2? I have this memory of light bulbs being brighter wired in parallel than in series. Assuming brighter could also mean hotter, it might explain your lower than anticipated temperatures? Quote Link to comment Share on other sites More sharing options...
½cwt Posted March 21 Report Share Posted March 21 Two 4 ohms in series is 8 ohms. Two 4 ohms in parallel is 2 ohms (but splits as half the applied voltage on each part of the parallel circuit). Quote Link to comment Share on other sites More sharing options...
Jon61 Posted March 21 Report Share Posted March 21 46 minutes ago, ½cwt said: Two 4 ohms in series is 8 ohms. Two 4 ohms in parallel is 2 ohms (but splits as half the applied voltage on each part of the parallel circuit). Your equivalent resistances are correct, but your bit in brackets is not right I'm afraid. If the resistances are in parallel, the full supply voltage is applied to both of them, as they are both connected directly to the power supply. It's when they are connected in series, and the supply voltage (= potential difference) has to fall from the full supply voltage down to zero in two stages, that less than the full supply voltage applies across each resistance (in this case, half across each, as the resistances are equal). Quote Link to comment Share on other sites More sharing options...
Sanky Posted March 21 Author Report Share Posted March 21 (edited) 4 hours ago, TV8 said: Thinking about this, doesn't connecting the elements in series increase the resistance compared with in parallel if connecting 4 down to 2? I have this memory of light bulbs being brighter wired in parallel than in series. Assuming brighter could also mean hotter, it might explain your lower than anticipated temperatures? Correct 2 heating elements at 0.8ohm each, wired in series would be 1.6 ohm. @K.I.T.T. there are 2 connections under the seat for each element disconnect them and measure the resistance. Or measure like above to check the total resistance. Your fault sound like one of the elements is open circuit if the LEDs on the switch are coming on and off. If you disconnect the elements you will get the same result Edited March 21 by Sanky 1 Quote Link to comment Share on other sites More sharing options...
½cwt Posted March 21 Report Share Posted March 21 6 hours ago, Jon61 said: Your equivalent resistances are correct, but your bit in brackets is not right I'm afraid. If the resistances are in parallel, the full supply voltage is applied to both of them, as they are both connected directly to the power supply. It's when they are connected in series, and the supply voltage (= potential difference) has to fall from the full supply voltage down to zero in two stages, that less than the full supply voltage applies across each resistance (in this case, half across each, as the resistances are equal). Sorry, wrong way round... Quote Link to comment Share on other sites More sharing options...
Menoporsche Posted April 26 Report Share Posted April 26 So on the thread about 987 seats linked above, we learned that PIWIS shows the cabin temp sensor has a role to play at least in the 987; it will switch the seat heating off if it thinks cabin temp is over 40degC (!). Cabin temp sensor is part of the aircon unit... Two stage heating appears to be controlled by pulsing the 4 heating pads, rather than applying to two different sets of pads with different resistance The 987 handbook (I think? Screenshot posted) actually describes how they work, with limited heating up periods on Level 1 and Level 2 lasting up to 9 and 11 minutes respectively, then the control unit switches to "continuous" phase and drops L2 power to 40% and L1 power to 14%. Meanwhile @DorsetWurzel posted in a 986 thread how he had retrofitted his: make sure you get the switches with the plugs and some loom and seats with the plugs to connect onto the seats and part of the wiring loom, 9 apart were brilliant and stripped the drivers side back to the fusebox, I had to make up some of the loom, but the was it. as for fitting, rake out you old seats, I depinned the red/violet power wire and the 3yellows and one ground from the supplied vehicle seat plug and populated the plug already on my car, you have to remove locking tabs (blue) on the plugs to do this and slide an end cap off to remove the smaller multi plug for the 3 yellow and one brown go to go in. once you have populated the seat plug you need to run the 3 wires to the switches, you do not have to follow the factory route! This will save you a ton of time. I went literally from under the seat up the side of the tunnel to where the switches are, less than a metre. you will have two wires left on the switches to connect, blue grey with red dots and a brown, you can connect both your ground and blue grey to the same colour wires in the electric window switches, this will save you a ton of time also. The blue grey is a 1.5v wire, so don’t try and wire it to a 12v supply! the thin brown that you connected with the yellows, just needs to go to ground. Earth points are under each seat. this leaves you the red violet, run this down the sill, to the fusebox, and on the top row is an unpopulated fuse space connect your wire there and fit a 25a fuse. Plug everything in and jobs jobbed.. Quote Link to comment Share on other sites More sharing options...
Menoporsche Posted April 26 Report Share Posted April 26 And Danncus suggested looking on ebay for VAG crimp repair terminals 000979227E for a tidy connection to the fusebox. https://www.ebay.co.uk/itm/126032837470 Quote Link to comment Share on other sites More sharing options...
Fat Rat Posted April 26 Report Share Posted April 26 Love the thread. But can’t get my head round why you would want heated seats in a car that has a great big heater behind the seats? Nice in a 356 maybe. 😬🤪😂 Quote Link to comment Share on other sites More sharing options...
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