all heated seat switch circuits

[DMonahan]

I have a 2005 town car Signature L. The illuminated switch on the front switch did not operate. I played with it and got it working, Then when I attached the door panel , it failed to operate completely. All the other switches worked, but they then all failed when I attached the passenger front door panel. I removed the passenger front door panel, but this did not restore the failures for all four switches. I checked the appropriate fuses and they all appear good. I tried to inspect the wiring on the front passenger switch and it appears to be okay. The default appears to be common to the circuitry to all four seat heat switches. Is there a fuse that controls the circuitry to all four switches or is there another issue that I am missing. Any thoughts. Thanks Dennis Monahan

 

[Action]

There are 3 electrical failures. Only 3.
A short circuit (Very rare in automotive DC circuits) where the power side wire contacts the return side wiring with no electrical load.
A grounded circuit where the power side contacts the metal part of the vehicle or the common ground.
An open circuit where the wiring is NOT connected either on the power side or the return side.

The first two situations, power will flow at a rate greater than design. And for the most part the wiring can not handle the current flow. Will heat up and could cause a fire. The protection to prevent those situations is a fuse or a circuit breaker.

If there is a failure for a given electrical function AND the circuit protection is intact, most likely the situation is an open circuit. The power flows to a point and because the circuit is open at that point, power goes no further. The variation to this is a poor connection. There is a connection. However, because the connection is dirty or not complete, power does not flow past that point. Either of these can occur on the power side or the return side. To diagnose this situation a wiring diagram and a test light are really all that is needed. Follow the power to the load. Then follow the return side to the vehicle ground reversing the test leads.

Action

 

[DMonahan]

I understand the information that you have provided, but why would the situation that you have described affect all four switches .... the front left and right and the rear left and right ?

 

[etinpa]

Wiring Diagrams for your use...

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[DMonahan]

Thank you That's amazing

 

[Action]

I understand the information that you have provided, but why would the situation that you have described affect all four switches .... the front left and right and the rear left and right ?

There is something electrical common to those four.
Which means start the diagnosis where power is coming into the system from the Central Junction Box. There is a fuse there and you stated the fuse is good.
The starting point would be to check for power at the fuse. Both sides.

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[DMonahan]

There is something electrical common to those four.
Which means start the diagnosis where power is coming into the system from the Central Junction Box. There is a fuse there and you stated the fuse is good.
The starting point would be to check for power at the fuse. Both sides.

Action

Got it thanks for your help. Just to be clear about the fuse. Can you advise the number where the fuse is located and does this fuse control all four heat switches. I really appreciate your help.

 

[DMonahan]

Just to be clear about the fuse. Can you advise the number where the fuse is located and does this fuse control all four heat switches. I really appreciate your help.

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[Action]

I am a little confused. You stated in post #1, ". I checked the appropriate fuses and they all appear good."
Did you or did you not check the appropriate fuse?

All circuit protection (including fuses and their locations) are shown in the owner's manual.
If you do not have one, you can always go to Lincoln.com

https://www.lincoln.com/support/vehicle/town-car/2005/owner-manuals/

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[DMonahan]

I'm sorry . I didn't mean to confuse you. I did check the approximate fuses that I could find in the owner's manual, but could not find one fuse that controls ALL four circuits. So what I shall do when it cools down up here in NY ( today was 102 degrees) is to pull out and inspect ALL the fuses in the entire system. What I suspect is that there is a single wire that is either open or shorted that has affected all four circuits . I can not tell you how very much I appreciate all the time and effort that you have give to me in this project. Do you beiieve that a single wire that is either open or shorted that could affect ALL four circuits . Thanks again.

 

[DMonahan]

I have specifically checked the following fuses in the passenger compartment : #9 7.5 amps "heated seat switch illumination" , #31 10 amps ( heated seats module ). In the Power Distribution Box : #16 20 amps "heated seats" , and # 118 20 amps "rear heated seats" . As I have indicated , I shall inspect ALL fuses in the chance if I find one that is blown , it MIGHT affect one of the four circuits. We"ll see.

 

[etinpa]

OK… let’s trace all of the wiring diagrams I posted.

Control for the front seats feeds from BJB F2 through CJB F9
Power for the front seats feeds from BJB F16 & F1 through CJB F31
Rear seats are from BJB F1 through CJB F31 & F118
The BJB F2 through CJB F9 circuit looks like backlighting only

Looks like the common feed for all heaters is the circuit from F1 in the BJB through F31 in the CJB.

When testing, note the CJB F31 only has power when the key is in the RUN position.

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[DMonahan]

OK I'll trace all and see what I get. Thanks again