Restoring Auction-bought 2001 Cobra - No Power Door Locks

[foofinator]

Hello Stangnet.

This is my first post here, but I am a long-time Mustang fan. I just added a sixth Mustang to my fleet (https://www.instagram.com/teamflyingbanana/ for pictures of said fleet) -- a 2001 Mustang Cobra convertible I bought at Copart, which I am in the process of restoring.

I'm having a frustrating issue with my power door locks. When I use either the passenger or driver side switches (either lock or unlock), the GEM clicks, but the lock actuators do nothing. Nor is there any power to the wires that go to the actuators.

So far, I've checked for continuity between the GEM and the wires that go to the driver door actuator (red and orange and white and red), and that was OK. I also replaced the GEM with a junkyard unit today, and I have the same issue. My thinking was, if the GEM clicks when I hit the switches, the switches are fine. And, if I have continuity between the GEM and the actuators, it must be the GEM. I was wrong.

In case it helps, I did finally get all four windows working, which I understand also go through the GEM, so maybe its not a ground?

Any thoughts on what I should look at next? I've done some extensive searching of Stangnet (through Google), and didn't see a solution, though I could tell members here have a lot of expertise. This door lock issue is really slowing down the progress on the restoration. I'd like to get this fixed up before I finish the carpet and reinstall the door panels.

Thanks in advance!

 

[wmburns]

Double check fuse F2.19 has +12 volts in and out. Use a KNOWN good ground for testing.

1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271

If this were my car I would double check the ground(s) to the GEM itself. These are the black wires and black wires with a white stripe. The main GEM ground is behind the center console. I would also verify the ground all the way back to battery negative. Here's some information on how to perform voltage drop tests.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Since you know where the GEM is and have access to it, here's my recommendation on how to split the problem as to where to focus further trouble shooting. Using a volt-ohm meter (VOM) (or a test light) probe GEM terminals #7(RD/OG) and #9(RD/WH). Now attempt to lock/unlock the driver's door. NOTE to see if there is any voltage present.

IF there is voltage at GEM #7/#9 THEN the problem is between the GEM and the door locks. Either in the wiring or door solenoids.

IF there is NO voltage at GEM #7/#9 THEN more tests are needed to narrow down.

Note, While I have never replaced a GEM there is a possibility that the GEM may need to be reprogrammed after swapping. My Ford service manual makes reference to this.

 

[foofinator]

Thanks, and happy holidays.

I will double check the fuse, and I will pull the radio bezel and radio to check the ground behind them. I had tested that ground indirectly (this could have been advice from one of your older posts) via the cigarette lighter ground (nearly 0 ohms). I did not test it all the way back to the battery. I just replaced the entire interior, and I hate to remove interior panels if I don't absolutely have to in order to avoid breaking the old plastic - I'll suck it up and do it and will be careful.

In addition to there being no resistance between the GEM and the driver's door actuator (testing continuity on the RD/OG and RD/WH wire), I did verify that the GEM is not providing voltage to those wires. If everything checks out with the fuse and the grounds, do you have any thoughts regarding the further tests mentioned in your post?

Thanks!

Jeremy

 

[foofinator]

Ok, so I have the shifter bezel, radio bezel, and radio removed. I don't see anything that looks like a ground back there - can you help point me in the right direction? Unfortunately, the previous owner did some serious hacking of the harness, so I'm glad I removed it. Almost looks like there was a small electrical fire at one point.

 

[foofinator]

Found the grounds! In case anyone else is looking for them - they are G203 and G204 in the picture below. Unfortunately, mine are in great shape, so that's not my problem.

 

[wmburns]

Now we need to confirm that the GEM is actually getting a good signal. Using the VOM or test light confirm power between GEM #20(LG) and #18(VT) while attempting to lock/unlock the doors using the driver's side buttons. The test light should light each time the lock/unlock button is used.

IF no power then either there's a wiring fault between the switch and GEM or the switch is bad. More tests are needed to determine which it is.

IF power is seen, then the problem is in the GEM.

Note about grounds and ground testing. Measuring zero ohms does not ensure that the circuit is able to carry large currents. Further, having a good ground at G203/G204 does NOT ensure there actually is a good ground path all the way back to battery negative.

The best way to test/confirm this ground is by loading it. For example using a test light and a scrap piece of wire extend the pig tail of the test light to battery positive. This should cause the test light to light up bright whenever the probe (tip) is touched to ground. ALWAYS confirm that the test light works before using it (IE touch to battery negative to confirm the light works). Now use the test light tip to positively confirm each ground point at the GEM produces a bright test light. Then you will know positively the ground path all the way back to battery negative is good.

 

[foofinator]

Thank you for your help wmburns.

Finally located the problem. Most of the wiring diagrams I found did not show how the GEM receives power for operating the locks, but I finally found a wiring diagram that did. Power for the locks comes into the GEM through a yellow/green wire, which is fused at location 12 in the underhood fuse box. I did not have any power coming through this wire.

While I could have sworn I tested all of the fuses, I must not have. The fuse appeared to be fine, but was shot. Once I replaced it, the locks worked. Interesting thing is the manual says fuse 12 is also for the power windows - my power windows worked even though this fuse was blown.

Tail tucked between my legs, I spent the next couple of hours reassembling the car. Totally could have avoided days of troubleshooting, but live and learn.

I just hope this helps someone else!

 

[foofinator]

I found the diagram mentioned in my last post - it paints a much more complete picture than others floating around the internet.