foothilltom

Hey guys, just for "closure" (as often there is none in these threads), I chose to sell the 2nd gen C4 I had bought as a stop-gap (per my original description).  Son limped the car up from LA and I set about re-building his original C4 first gen tranny over a 3 week period.  Never had done that before, so I was quite uneasy.  Took my time, took a zillion photos, and found at least 3 significant issues that would have explained the bad behavior.
Anyway, C4 is back in, new servo, o-rings, bands, clutches, steel, thrust washers, bushings, seals, etc. and the Stang is back on the road.  Only set us back the price of the master rebuild kit so I'm going to call it good for now.  I'm sort of trivializing a rebuild that my hair standing on end at times, but it all worke dout.
Thanks again for all your input.  
Tom

Hey guys, just for "closure" (as often there is none in these threads), I chose to sell the 2nd gen C4 I had bought as a stop-gap (per my original description).  Son limped the car up from LA and I set about re-building his original C4 first gen tranny over a 3 week period.  Never had done that before, so I was quite uneasy.  Took my time, took a zillion photos, and found at least 3 significant issues that would have explained the bad behavior.
Anyway, C4 is back in, new servo, o-rings, bands, clutches, steel, thrust washers, bushings, seals, etc. and the Stang is back on the road.  Only set us back the price of the master rebuild kit so I'm going to call it good for now.  I'm sort of trivializing a rebuild that my hair standing on end at times, but it all worke dout.
Thanks again for all your input.  
Tom

Yup, it is a terrible design.  Ford went to plastic housings in 1971.  This problem was one of the reasons I make hard-wired dash cluster harnesses to get rid of the circuit card, which was often blamed for gauge problems.  To replace the circuit card, you must undo the nuts holding the gauge in place, which allows the gauge to move and have the posts contact the metal housing.  But only without the circuit card, you can test continuity between the posts and the chassis: should be very high.  If you see 14 or 0 ohms, then you know one of the posts is touching.  With the circuit card in place, a touched post causes all the non-ammeter gauges to read 14 or 0 ohms to metal chassis, and you can't tell which one is causing the problem.

Nice work, Tom. That's a common problem, often difficult to diagnose. You're right, it's not a great design.

Last update for this post. After much troubleshooting, the fuel gauge problem was a re-assembly issue with the cluster. Even though the insulation brackets were in the right spot, the posts on the back of the gauge were contacting the cluster housing, grounding them out. I put some electrical tape around the inside of the housing where the posts slide through and it worked. Seems like a bad design, in my opinion, but it worked for 15 years before I messed with it so what are you going to do?
Got the idea from this video I found in an old forum. Hope it helps somebody else. 

Last update for this post. After much troubleshooting, the fuel gauge problem was a re-assembly issue with the cluster. Even though the insulation brackets were in the right spot, the posts on the back of the gauge were contacting the cluster housing, grounding them out. I put some electrical tape around the inside of the housing where the posts slide through and it worked. Seems like a bad design, in my opinion, but it worked for 15 years before I messed with it so what are you going to do?
Got the idea from this video I found in an old forum. Hope it helps somebody else. 

***SOLVED***
First off, I would like to thank you all for your help. Between all of your insights I was able to figure out the problem.
LONG story short, I hooked a 9V battery to some speaker wire and started poking my fully assembled cluster (now on my kitchen counter) until lights started turning on. To my surprise, sometimes almost all of the lights turned on! WEIRD! After a while I noticed a pattern that when I put voltage across each light socket, one of two things would happen: 1) Only two lights would light up OR 2) All of the other lights besides two would light up. This would happen after changing the polarity of my test by reversing which side on each socket I had the "positive" and "negative" cables from the 9V battery. 
I then checked the forum to post my findings and saw what @danno had said about the insulating brackets so I took apart the cluster again and made sure they were in the correct position. Once I re-assembled the cluster and repeated my earlier test, I got the same results EXCEPT now two different bulbs were lit up (or not lit up depending on the cable polarity).
Once I bashed my head against a wall a few more times, I thought back to what @Midlife said about polarity, and even though the bulbs I purchased have reversible polarity, and, therefore, should not care how they are installed, I thought maybe, just maybe, technology back in 1969 wasn't set up to handle reversible polarity.
I then, in the proper "positive/negative voltage flow" scenario, removed and rotated each bulb, that wasn't lighting up, 180 degrees and BOOM. All bulbs work as intended. What a relief.
TLDR: Even reversible polarity LED bulbs bought from modern manufactures are not reversible in this context. I have no idea why and random chance of how I chose to install each bulb has been my downfall all along. I will definitely be marking my lights and light sockets with a pen from here on out.
Anyways, a test drive to make sure my gauges were working revealed that the only casualty is my fuel gauge, which does not work anymore. @danno this gauge had the insulating brackets in the correct place all along so i'm not too sure why it's suddenly not working, but I am taking the win for tonight.
Pictures attached of my 9V test for those who are curious. I hope this thread helps others who have issues with after market LED's. 
 

***SOLVED***
First off, I would like to thank you all for your help. Between all of your insights I was able to figure out the problem.
LONG story short, I hooked a 9V battery to some speaker wire and started poking my fully assembled cluster (now on my kitchen counter) until lights started turning on. To my surprise, sometimes almost all of the lights turned on! WEIRD! After a while I noticed a pattern that when I put voltage across each light socket, one of two things would happen: 1) Only two lights would light up OR 2) All of the other lights besides two would light up. This would happen after changing the polarity of my test by reversing which side on each socket I had the "positive" and "negative" cables from the 9V battery. 
I then checked the forum to post my findings and saw what @danno had said about the insulating brackets so I took apart the cluster again and made sure they were in the correct position. Once I re-assembled the cluster and repeated my earlier test, I got the same results EXCEPT now two different bulbs were lit up (or not lit up depending on the cable polarity).
Once I bashed my head against a wall a few more times, I thought back to what @Midlife said about polarity, and even though the bulbs I purchased have reversible polarity, and, therefore, should not care how they are installed, I thought maybe, just maybe, technology back in 1969 wasn't set up to handle reversible polarity.
I then, in the proper "positive/negative voltage flow" scenario, removed and rotated each bulb, that wasn't lighting up, 180 degrees and BOOM. All bulbs work as intended. What a relief.
TLDR: Even reversible polarity LED bulbs bought from modern manufactures are not reversible in this context. I have no idea why and random chance of how I chose to install each bulb has been my downfall all along. I will definitely be marking my lights and light sockets with a pen from here on out.
Anyways, a test drive to make sure my gauges were working revealed that the only casualty is my fuel gauge, which does not work anymore. @danno this gauge had the insulating brackets in the correct place all along so i'm not too sure why it's suddenly not working, but I am taking the win for tonight.
Pictures attached of my 9V test for those who are curious. I hope this thread helps others who have issues with after market LED's. 
 

Hey guys.  It's been about 8 years since I darkened the doorway of this great forum.  Hope everybody is still alive and kicking.
This game called life has unfolded and the 69 302 coupe my son and I built together oh so many moons ago has once again landed in my garage.  My son is 25 now and off living his life and has no place for the stang.  So it sits with me now.  Bwah-ha-ha-haaaaaaaaaaaaaaaa.
Anyway, I would like to get back on the horse (pun intended) and start asking some questions.  Just thought I should say "howdy" first before just shamelessly picking your brains.
Hope all is well.
FoothillTom

Hey guys.  It's been about 8 years since I darkened the doorway of this great forum.  Hope everybody is still alive and kicking.
This game called life has unfolded and the 69 302 coupe my son and I built together oh so many moons ago has once again landed in my garage.  My son is 25 now and off living his life and has no place for the stang.  So it sits with me now.  Bwah-ha-ha-haaaaaaaaaaaaaaaa.
Anyway, I would like to get back on the horse (pun intended) and start asking some questions.  Just thought I should say "howdy" first before just shamelessly picking your brains.
Hope all is well.
FoothillTom

Hey guys.  It's been about 8 years since I darkened the doorway of this great forum.  Hope everybody is still alive and kicking.
This game called life has unfolded and the 69 302 coupe my son and I built together oh so many moons ago has once again landed in my garage.  My son is 25 now and off living his life and has no place for the stang.  So it sits with me now.  Bwah-ha-ha-haaaaaaaaaaaaaaaa.
Anyway, I would like to get back on the horse (pun intended) and start asking some questions.  Just thought I should say "howdy" first before just shamelessly picking your brains.
Hope all is well.
FoothillTom