Seat Heater Repair 80 90 CQ

Andrew Lundy fast928 at
Tue Jan 23 16:12:51 EST 2001

This is a re-post of my earlier message.  I made one small clarification
This is the procedure that I used to repair the seat heaters on my 80Q.
This procedure will be able to be applied directly to the `88-`91 80/90/CQ.
This procedure will also work on the 4000/5000/100/200/S4's as well as the
later 90 models, but the wire colors and a few other details may differ

Tools needed:

Circuit tester
10 mm socket (possibly)
Ratchet w/ small extension (possibly)

The connectors:

Locate the green six point connector located under the seat.  You should be
able to gain enough access to this connector by simply sliding the seat all
the way back (manual seats).  Pull the connector apart.

Here is a (very) rough picture of the connectors---label as shown as if
looking into connector:

Connector A:

:X(1)  *  X(2)     X(3)   :
:X(4)  *  X(5)     X(6)   :
(This connector goes under the carpet and leads to the auxiliary relay
X - Denotes a metal (female type) electrical connector
* - Denotes empty (void) space---helps better relate orientation

Wires colored as follows
Drivers Side:
(1) - Brown
(2) - Black/White
(3) - Black/Yellow
(4) - Brown/Blue(Jumper to 5)
(5) - Brown/Blue
(6) - Brown/Black

Passenger Side:
(1) - Brown
(2) - Green/Black
(3) - Black/Red
(4) - Brown/Blue(Jumper to 5)
(5) - Brown/Blue
(6) - Brown/White

Connector B:
:---(1)  * ---(2)  ---(3)   :
:---(4)  * ---(5)  ---(6)   :
(This connector goes into the seat)
--- - Denotes a metal spade (male type) electrical connector
* - Denotes plastic tab---helps better relate orientation

Colored as follows
Drivers Side/Passenger Side(both are the same):
(1) - Brown/Blue
(2) - Brown/Blue
(3) - Brown/Black
(4) - Brown
(5) - Black/White
(6) - Black/Yellow

Testing procedure:

1) Turn the ignition to the on position---warning lights on
2) Flip on the seat heater switch
(Leave this for the entire testing procedure)

Step one:
The plugs need to be connected for "Step 1".  If the plugs are not
connected, this test procedure will not work.  After "Step 1" is completed
the connectors can be pulled apart for all of the remaining tests.

The first step is to be sure that there is power going to the seat. Find a
good known ground in the car, I like to use the top of the cigarette lighter
(the metal at the very top), hook one side of the circuit tester to the
ground and the other side into Connector A (3).  If you have power (light)
then skip to step three.

Step two:
If you don't have power then remove the panel under the steering wheel and
locate the auxiliary relay panel (Ratchet and Socket needed).  Locate the
appropriate relay, #13 & #14 (pre-'91) or #14 and #18 (`91).  Remove the
relay and look at the bottom of the relay, near the prongs there will be an
"h" on one and another will have a "15" by it (along with markings for all
the other prongs).  Locate where the prongs of the "h" and "15" plug-in to
the relay panel.  Test the "h slot" (in the relay panel) with the circuit
tester to be sure it has power.  If there is no power, check the fuse, if
fuse is okay locate the break in the wiring between the fuse and relay
If "h slot" has power then test the continuity of the wire between the relay
and the seat.  To do this put the multimeter in the lowest resistance (ohms)
range, put one end into the "15 slot" and place the other end in Connector A
(3).  You should get a very small resistance between the two, if you get no
reaction from the multimeter, trace the wire and repair the break.  If you
obtain a resistance test the function of the switch.  To do this, use the
circuit tester and connect it to ground and the "86 slot" in the relay
panel.  Also check the "P slot" for power......this should barely light only
in the first two positions and then it shouldn't light.  If power is not
attained at both slots then repair/replace the switch or wiring between.  If
power is attained at both slots then swap the relay with the other one and
return to step one (or see if the seat gets hot with the new relay in).

Step three:
This step requires checking the continuity of the heating elements.  To do
this use Connector B.  Use the lowest resistance setting on the multimeter
and connect (6) and (2).  Again, you should end up with a very small
resistance; if not, then the "butt" heating element has a break in it.  To
fix this check here:

If you obtain a small resistance then, on Connector B, use the multimeter
and connect (1) and (4).  If you obtain a small resistance then go to step
four.  If no resistance is returned then there is a break in the "backrest"
heating element.  There are two methods that can be used to fix this.

 Method one:  Follows similar to the following link except your in the

 Method two:  You can simply splice wires on Connector A and bypass the
"backrest" heater.  If you choose to do this, on Connector A, cut the jumper
wire, then splice the wire from (5) into wire (1).  You can leave the loose
wire at (4) disconnected.

Step four (two options):
Connect the circuit tester to a known voltage source and to Connector A (1).
If there is no power (light) then trace the wiring and repair break.  If you
get power you made a mistake somewhere, go back to step one and follow the
procedure again (or your seat heater works)!!!


Set the multimeter to the lowest resistance setting and check for
continuity.  To do this place one lead on a known ground and the other lead
to Connector A (1).  Again, you should get small resistance.  If no
resistance is returned then trace the wiring and repair break.  If there is
a little resistance then you made a mistake somewhere, go back to step one
and follow the procedure again (or your seat heater works)!!!

Good Luck!!!
Andrew Lundy
fast928 at
90 80q
91 90
95 90q

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