Seat heating
02-19-2017, 09:54 AM
#16
Rennlist Member
I pursched replacement seats for my car from Mark during his sale. These seats are 12 way power and have heat. As I stated earlier I have a good fuse in #44. I have tested power at the switches and there is power. i have followed the WSM for the 1990 as that is what I have wiring diagrams for. These seats must be from a pre-89 car as the test steps in the manual do not show how to test the switch without the potentiometer and the manual says "as of MY-89". I can only assume the potentiometer came out in 89.
So, I guess I need to do as you said and take the seats out and test each element for resistance to see if one is broken.
Do you have the pre-89 steps to test the switch or just assume that since the two wires have power I am good on the switch part of this and move on?
So, I guess I need to do as you said and take the seats out and test each element for resistance to see if one is broken.
Do you have the pre-89 steps to test the switch or just assume that since the two wires have power I am good on the switch part of this and move on?
Last edited by jeff spahn; 02-19-2017 at 11:15 AM.
02-19-2017, 11:13 AM
#17
Instructor
Thread Starter
NEVER assume anything when it comes to electricity/electronics ! 
!
To be 100% sure about the switch, I would remove the seat heating relay. That way you are sure to test only the switch.
Terminal 1 of the switch should measure 12V
Terminals 4 & 6 of the switch should measure 12V when you press the according switch area.
When that is the case you can be sure that the switch is ok.
You can then measure at pins E & A of the relay socket, still with no relay. Again you should have 12V on these E & A terminals when pressing the switch, 0V when pressing nothing.
Once that is ok you are sure that all wiring between switch & relay is ok.
If you plug in the relay and measure only 5 V with switch depressed and 0V with switch pressed (on which terminals by the way???) , I can’t tell you if that is ok since I don’t have the circuitry of that relay.
Further you can connect your multi meter in Voltage mode between terminals 87 & 31 (ground) of the relay. On these terminals you should measure 12V for a given time after pressing one of the switches.
When that is the case you know that the relay is working: with every press of the button the heating elements (your Voltmeter in this case) gets 12V.
When you don’t measure anything, check the 12V at terminal 15 of the relay. If no voltage there you have a power problem to the relay even with fuse #44 ok.
Please provide some pictures of the seats when removed from the car.
Can you please also post the electrical drawings you have, then we both look at the same stuff.
Hope this helps!
Have fun!!
Regards
!To be 100% sure about the switch, I would remove the seat heating relay. That way you are sure to test only the switch.
Terminal 1 of the switch should measure 12V
Terminals 4 & 6 of the switch should measure 12V when you press the according switch area.
When that is the case you can be sure that the switch is ok.
You can then measure at pins E & A of the relay socket, still with no relay. Again you should have 12V on these E & A terminals when pressing the switch, 0V when pressing nothing.
Once that is ok you are sure that all wiring between switch & relay is ok.
If you plug in the relay and measure only 5 V with switch depressed and 0V with switch pressed (on which terminals by the way???) , I can’t tell you if that is ok since I don’t have the circuitry of that relay.
Further you can connect your multi meter in Voltage mode between terminals 87 & 31 (ground) of the relay. On these terminals you should measure 12V for a given time after pressing one of the switches.
When that is the case you know that the relay is working: with every press of the button the heating elements (your Voltmeter in this case) gets 12V.
When you don’t measure anything, check the 12V at terminal 15 of the relay. If no voltage there you have a power problem to the relay even with fuse #44 ok.
Please provide some pictures of the seats when removed from the car.
Can you please also post the electrical drawings you have, then we both look at the same stuff.
Hope this helps!
Have fun!!
Regards
02-19-2017, 11:20 AM
#18
Rennlist Member
Thanks! I am going to do that. I posted a pic as well in my last reply. Here's the wiring diagrams I have.
I'll have to get the seats out later today or tomorrow. I have memory seat on driver side and non memory on passenger. I'll start with passenger as that must have the relay instead of the funky memory module giant flat thing with all the plugs.
Oh, and I don't have sport seats, they are comfort seats.
I would like to try to find 9269 cable also from the Rennlist brain trust. I mean I'll bite the bullet and buy it ($145) if I have to but I don't know how to get power to the seats so everything works via the 14 pin seat connector.
Porsche 928 Wiring Diagram - 1990.pdf
I'll have to get the seats out later today or tomorrow. I have memory seat on driver side and non memory on passenger. I'll start with passenger as that must have the relay instead of the funky memory module giant flat thing with all the plugs.
Oh, and I don't have sport seats, they are comfort seats.
I would like to try to find 9269 cable also from the Rennlist brain trust. I mean I'll bite the bullet and buy it ($145) if I have to but I don't know how to get power to the seats so everything works via the 14 pin seat connector.
Porsche 928 Wiring Diagram - 1990.pdf
02-19-2017, 11:45 AM
#19
Instructor
Thread Starter
Well, when I asked for a picture, I mend a picture of the bottom of the seat to see the wiring/relays and so on
Attached:
1) Part of the drawing of a ’88 schematic diagram. As you can see, 95% identical to the ’90 one.
2) Picture of the 14 way connector of passenger seat, only 3 are used.
3) Picture of the 14 way connector of driver seat with memory, 13 of them are used.
If I remember well pins 1 & 3 are used for power.
If in doubt, check on the car first which terminals brings power to the connector.
Do you have a 12V regulated power supply, or another car battery?
May be easier (and saver) to use instead of looooong wires between the terminal in the car and the one at the seat outside the car (I you see what I mean ?
?)
I used a regulated power supply when investigating my heating problem.
Attached:
1) Part of the drawing of a ’88 schematic diagram. As you can see, 95% identical to the ’90 one.
2) Picture of the 14 way connector of passenger seat, only 3 are used.
3) Picture of the 14 way connector of driver seat with memory, 13 of them are used.
If I remember well pins 1 & 3 are used for power.
If in doubt, check on the car first which terminals brings power to the connector.
Do you have a 12V regulated power supply, or another car battery?
May be easier (and saver) to use instead of looooong wires between the terminal in the car and the one at the seat outside the car (I you see what I mean ?
?)I used a regulated power supply when investigating my heating problem.
02-19-2017, 12:44 PM
#20
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
You talk about a '90 car but also mention "the seats you put in" where were these from? and what happened to the original seat(s). Did you just add a different passenger seat? Are both configured the same way?
Did you take the seats out to test? if so can we see pictures of the underside?
Memory seat for '90 should have the seat heater timed on and variable level seat heating (with potentiometer control) and the heating relays in the main (large) relay controller unit. '87-'89 seats with memory have the simpler single power level timed on seat heating with the switch without the potentiometer. Seems this is what you have - seats from an earlier car for some reason. Even in this case the seat heating relay is integrated into the (large) seat relay controller in much the same way.
Locate the 2 pin connector that feeds the heater circuits in the seat - it connects to the switch (brown wire) and to the main relay controller white wire. Brown is ground and White is seat power.
You can test the voltage on the white wire with the connections still made - or pull the connector and on the control side connect up pigtails to a load between White & Ground (high power bulb is OK). Here you also need to connect this brown wire to the main Ground (in) connection on the seat - since the seat elements ground separately. The small brown wire is the sense line to the switch - not the power supply to the elements.
Then see what happens when you operate the switch with power to the module as normal (e.g. best to have the seat connected to the car - awkward). You must have the ignition on for seat heating to operate. Monitor voltage on the White wire.
Most likely cause is still broken seat heating elements - they have a finite life, partly through electrical usage but also just age and usage stress. If the controls are working you can adap modern type heating elements that are more robust (they don't have a single element failure point). Of course to do that you need to remove & reinstall all the seat covers - but you'd need to do the same for the stock replacement elements (if still available). Second most likely cause is connections not made correctly (or broken wires).
Another possible test method is to just measure the resistance and/or apply 30A fused power to the seat elements after you unplug the connector and see what they do? helps to isolate the failure point.
Alan
Did you take the seats out to test? if so can we see pictures of the underside?
Memory seat for '90 should have the seat heater timed on and variable level seat heating (with potentiometer control) and the heating relays in the main (large) relay controller unit. '87-'89 seats with memory have the simpler single power level timed on seat heating with the switch without the potentiometer. Seems this is what you have - seats from an earlier car for some reason. Even in this case the seat heating relay is integrated into the (large) seat relay controller in much the same way.
Locate the 2 pin connector that feeds the heater circuits in the seat - it connects to the switch (brown wire) and to the main relay controller white wire. Brown is ground and White is seat power.
You can test the voltage on the white wire with the connections still made - or pull the connector and on the control side connect up pigtails to a load between White & Ground (high power bulb is OK). Here you also need to connect this brown wire to the main Ground (in) connection on the seat - since the seat elements ground separately. The small brown wire is the sense line to the switch - not the power supply to the elements.
Then see what happens when you operate the switch with power to the module as normal (e.g. best to have the seat connected to the car - awkward). You must have the ignition on for seat heating to operate. Monitor voltage on the White wire.
Most likely cause is still broken seat heating elements - they have a finite life, partly through electrical usage but also just age and usage stress. If the controls are working you can adap modern type heating elements that are more robust (they don't have a single element failure point). Of course to do that you need to remove & reinstall all the seat covers - but you'd need to do the same for the stock replacement elements (if still available). Second most likely cause is connections not made correctly (or broken wires).
Another possible test method is to just measure the resistance and/or apply 30A fused power to the seat elements after you unplug the connector and see what they do? helps to isolate the failure point.
Alan
02-19-2017, 03:36 PM
#21
Rennlist Member
You talk about a '90 car but also mention "the seats you put in" where were these from? and what happened to the original seat(s). Did you just add a different passenger seat? Are both configured the same way?
Did you take the seats out to test? if so can we see pictures of the underside?
Memory seat for '90 should have the seat heater timed on and variable level seat heating (with potentiometer control) and the heating relays in the main (large) relay controller unit. '87-'89 seats with memory have the simpler single power level timed on seat heating with the switch without the potentiometer. Seems this is what you have - seats from an earlier car for some reason. Even in this case the seat heating relay is integrated into the (large) seat relay controller in much the same way.
Locate the 2 pin connector that feeds the heater circuits in the seat - it connects to the switch (brown wire) and to the main relay controller white wire. Brown is ground and White is seat power.
You can test the voltage on the white wire with the connections still made - or pull the connector and on the control side connect up pigtails to a load between White & Ground (high power bulb is OK). Here you also need to connect this brown wire to the main Ground (in) connection on the seat - since the seat elements ground separately. The small brown wire is the sense line to the switch - not the power supply to the elements.
Then see what happens when you operate the switch with power to the module as normal (e.g. best to have the seat connected to the car - awkward). You must have the ignition on for seat heating to operate. Monitor voltage on the White wire.
Most likely cause is still broken seat heating elements - they have a finite life, partly through electrical usage but also just age and usage stress. If the controls are working you can adap modern type heating elements that are more robust (they don't have a single element failure point). Of course to do that you need to remove & reinstall all the seat covers - but you'd need to do the same for the stock replacement elements (if still available). Second most likely cause is connections not made correctly (or broken wires).
Another possible test method is to just measure the resistance and/or apply 30A fused power to the seat elements after you unplug the connector and see what they do? helps to isolate the failure point.
Alan
Did you take the seats out to test? if so can we see pictures of the underside?
Memory seat for '90 should have the seat heater timed on and variable level seat heating (with potentiometer control) and the heating relays in the main (large) relay controller unit. '87-'89 seats with memory have the simpler single power level timed on seat heating with the switch without the potentiometer. Seems this is what you have - seats from an earlier car for some reason. Even in this case the seat heating relay is integrated into the (large) seat relay controller in much the same way.
Locate the 2 pin connector that feeds the heater circuits in the seat - it connects to the switch (brown wire) and to the main relay controller white wire. Brown is ground and White is seat power.
You can test the voltage on the white wire with the connections still made - or pull the connector and on the control side connect up pigtails to a load between White & Ground (high power bulb is OK). Here you also need to connect this brown wire to the main Ground (in) connection on the seat - since the seat elements ground separately. The small brown wire is the sense line to the switch - not the power supply to the elements.
Then see what happens when you operate the switch with power to the module as normal (e.g. best to have the seat connected to the car - awkward). You must have the ignition on for seat heating to operate. Monitor voltage on the White wire.
Most likely cause is still broken seat heating elements - they have a finite life, partly through electrical usage but also just age and usage stress. If the controls are working you can adap modern type heating elements that are more robust (they don't have a single element failure point). Of course to do that you need to remove & reinstall all the seat covers - but you'd need to do the same for the stock replacement elements (if still available). Second most likely cause is connections not made correctly (or broken wires).
Another possible test method is to just measure the resistance and/or apply 30A fused power to the seat elements after you unplug the connector and see what they do? helps to isolate the failure point.
Alan
Both seats have been replaced. I don't know what year they are from but as I referenced above with photo of seat controls they must be pre-89. Got them from Mark at 928 Intl. Driver seat is 12 way w/heat and memory. Passenger is 12 way with heat, memory is not present on the seat but I did add it to the car and I know have learned that it won't work with the big flat module on the bottom of the seat. Oh well, looks good on door anyway. I am going to build or buy a 10' extension cable from the car to the seat so I can work on them out of the car on a bench. I'll test the connection from relay or module to heater to heater to heater and see where the break is (advice given in the thread to me). If the heaters are dead, and I suspect they are based on what you two have said, I'll get new ones and put them in.
I'll let you guys know what I find and put it here.
02-26-2017, 10:52 AM
#22
Three Wheelin'
FWIW my guess is lack of continuity due to broken wiring in the seat heaters themselves. 12 way heated memory seats are special (time to make them Sport!) but the factory heating elements are pricey.
03-13-2018, 03:56 AM
#23
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They just act on the relay and that is all, 12v positive is fed from the relay through pin 87 at plug 2 to seat heating element in seat base cushion. There is a thermistor switch in the seat base that can go bad, and element can show continuity and still not heat. Test by bypassing seat cushion and test seat back. There is a capacitor circuit in the control box that functions like a timer to release the relay.
That is as far as I have gotten, my circuit now works for seat back, need to unwrap the seat cushion and check thermistor in there.
Try this link, I have the wiring diagram on my Google drive, hopefully this link works.
This in for is for 88 12 way power seats with memory.
For good measure I also pulled the control box out and resoldered the connection points for all plugs, they were cracked and looking rugged.
https://drive.google.com/file/d/1j7x...w?usp=drivesdk
03-14-2018, 02:01 AM
#24
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So now I have verified that each seat heating element works when wired indicidually, but they don't work when wired in series. Not sure why that would be the case. Any ideas? Using a 12v battery for power supply.