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Heated seats fixed (5k)

Several listers wanted to know how to fix their seat heaters before winter
sets in. The method was good for an 1987 5kcstq with leather seats, and
having electrical adjustment and position memory. I have no website, so
this post is probably headed for the archives.

SHORT VERSION: After you find the broken element, soldering nichrome
doesn't work. Crimp after twisting around a third conductor such as a
thicker solid copper wire section.  Substitute plastic ties in place of hog
rings when you put the seat back together.

Additional notes: Check out the connections between the feed wires that go
to and from the thermistor, which is located in the heating element pad. On
several seats, we found one of those wires broken right where it joins one
side of the thermistor wafer.  The thermistor is a separate unit that is
only in physical contact with a section of the resistance wire. It is glued
to the resistance wire, and can be peeled off, repaired, and reattached.
This was in addition to finding and fixing the burned spots in the actual
heating element pad.

Caution: Heater elements in the 4kq are very different than are described
here, and much harder to locate and diagnose.


The electrically adjustable leather front seats came out of the 87 5kcstq
easily by first removing the two front bolts that hold each seat to the
floorboard, and also removing the small bumpers at the ends of the  seat
track. Otherwise the seat won't easily slide out the back of the track.
Also, slice your carpet at the rear of the inner track, to ease that seat
runner from sliding under the carpet as it exits, and jamming the removal.
You can cut the carpet just after taking off the blade-like plastic trim on
top of the rear inner track (one screw).

We didn't disconnect the battery during our work, which made it possible to
use the power adjusters on the seats to get them into more favorable
positions. It would probably be a good idea to consider battery
disconnection once the seats are in full reverse position and just before
you start taking them out.

After you have the driver seat unbolted in front, you can tip it up toward
the steering wheel, block it in place, and get underneath with a flashlight
to pull apart the three electrical connectors: Seat belt sensor (white
plastic), Power for adjuster motors (brown, large, and hard to reach);
Actual seat heater power and thermistor wires (six prong two-color brown
and green plastic). These are all plastic-tied to adjacent structures. We
cut the plastic ties and replaced the ties at reassembly.

After unplugging the electricals, slide the seat backward and out onto the
rear passenger floor. (To avoid grease on the carpet, first cover with
disposable towel.)

To avoid fighting the steering wheel during seat removal, pivot the driver
seat and removed it headrest-first through the back door. Passenger front
seat comes out the front door pretty much the same way, but with fewer
electrical connections. Thorough vacuum cleaning of the carpet around the
seats is now possible prior to seat replacement, and will never be easier.


When you have the seats in the shop on the bench, find the plastic shields
on each side at the junction of the seat bottom and the seat back. These
have several almost invisible plastic push-pins holding them in place. Use
a punch to find them and remove them, otherwise you break off the tubes the
pins are in, and the shield is toast to re-install.

With the shields off, Go to the panel that contains the seat position
controls.   Unscrew the  two retaining fasteners (front and middle
screws)that hold the control panel covers to the underlying supports. 

Then take off the black caps from  the bolt heads at each pivot point for
the seat back. Under each black cap is a big Phillips-head screw. Take them
out on both sides. Now move the two-part control panel cover to a safe
location away from your work area.

Use a big screwdriver to pry the flat angular pivot plate up and off its
pin on the seat bottom,  doing first one side all the way, then the other.
The plate is springy enough to allow this.  Now the seat bottom is loose
from the seat back except for two wires. Don't apply undue stress on these
unsupported wires as you manipulate the seat components.


Again, without undue stress on the wires, tip both seat halves up on one
side and inspect the underside and rear of the bottom seat.

Start at either rear corner of the bottom seat, and locate the wire cable
that runs in a fabric tube all the way around the sides and front of the
seat cover. At each rear corner, it wraps up and around a metal ear of the
seat structure. This wire must be traced and un-bent/unwrapped from its
perch on the ear. Loosening either corner takes the tension off the lower
edge of the seat cover, making it easier to loosen at the other attachment
points on the sides and front and at the other corner.

At the front of the seat bottom there are two obvious pointed push-pins
that look like buttons holding the fabric under the front edge. Press these
pins out, after first loosening them with a flat bladed screwdriver, and
pull them the rest of the way with pliers.

On each bottom side, find a bent-over metal tooth about midway, holding the
seat cover. With pliers, bend the tooth out straight and pull the cover
from its snagged grip. You now have the front and sides free. 

Go to the back edge of the cover and massage, pry/tug the fold-over flap
from its metal slot all along the back of the seat bottom. If you get one
end loose, it slides out easily with some pulling with pliers and flat-blades.

You can now peel the seat cover up and off its block of seat foam.

With the rear, sides and front of the seat cover up, you can see where the
wires and hog-ring clips hold the center section of the seat cover in place.

Instead of removing each hog ring individually, I un-bent the looped end of
each foot-long support wire over which the rings are clipped, and I pulled
the entire wire out from the string of hog rings. It then required a few
careful snips with sharp scissors to get the tube of seam fabric (that
contained the support wire) away from each hog-ring clamp.

You now have access to the actual seat heater pad, which is held to the
sides and front of the foam with low-grade adhesive. It separates with some
effort and a little tearing of the foam.


You can inspect the surface of the pad and easily spot the burned areas
that identify broken resistance wires. Most of ours were along the outside
edge of the bolster, where the weight of the passenger or driver first
slams down on the seat and bends the element.

Using an Exacto knife, I dissected the wires out of the fascia of pad
material for about an inch and a half at both sides of the break.  I then
did a conductivity test between each end and the connector plug, to prove
that I had found the only break in that section. If you can't prove
conductivity, you are going to have to pin out the wire until you find the
other fault(s). By that, I mean poke pins into the resistance wire through
the insulation and do conductivity tests until you find good wire, then
work backwards until you isolate the break and fix it.

I shaved the insulation back along each end of the broken element for about
a half inch, twisted them tight individually and then twisted them together
in to a short stub, and then wrapped the stub around a section of solid
copper #16 wire and crimped the final structure with a commercial crimp
connector of the proper size.

We didn't have any faults in the seat backs, so I can't write about fixing
them. It appears that all our faults were due to passenger weight fatiguing
the bottom seat wires over years of daily use.


Retest the conductivity of all the circuits, make sure you find and check
the thermistor and its connections, and reassemble the seat using plastic
ties in place of the hog rings. Reassembly is the reverse of taking it apart.

Doyt Echelberger
87 5kcstq