Fuel & Temp gauge, dash lights

Heres one for the minds. I have a 75 Gran Torino. 351 W.  Im the second owner and about a year after purchase I started having an issue with the dash lights. The lights would flicker then go out. I could tap on the dash and they would come back on. I didn't really get into it  because I wanted to swap dash clusters with a Sport. Well  before I could do that my fuel & temp gauges went wacky on me. The fuel will read full and the temp would go all the way over to hot. I thought no big deal, its something with this cluster and I had already ordered  one. I figured I would change it out and problem solved, well that didn't happen. When I installed the new cluster I had the same issue. Ive done some trouble shooting, pulling the connector off the fuel sending unit (which is a new one) and tested the units IVR. My manual says if the voltage is steady that  the IVR is bad. So to eliminate that possibility I plugged the other dash back in and still the same issue. I don't think both IVR's could be bad. Does anyone know what the number ID's on the plug are for ? Im thinking my issue is with the plug going back thru the vehicle and  not the dash cluster. Thoughts anyone ?  

  Could the dash cluster be from a different vehicle, there are differences in the wiring terminations of different year gauge clusters and/or plugs. This may help:

Edited by aquartlow - 08-September-2015 at 12:22PM

^^^ what they said. you may need to trace down the individual circuits from the plug to the gauge one at a time, you may need to switch a couple of the wires around to match up with the sport cluster (i did on my dash conversion in my car) also--- if your original cluster had idiot lights, you need to change the oil and water senders to a gauge type (there is a difference) they fit the same but use a different resistance value for the gauge vs a light

Well heres an update. I had to order a new ignition module as mine died on me after pulling the car in front of the garage door. Well during that time of waiting for the new to arrive I decided to do some more trouble shooting. Seems my plug that goes into the PCB of the cluster is the 77-79 (some 76models) D7GF 10C956 BA. The #1 pin being the purple with white stripe. After installing the ignition module  I plugged in the dash cluster and all my dash lights started working. I had switched over to LED's but  when I plugged it in earlier nothing  would come on. So, maybe the module had something to do with it (sounds unlikely ,but... you never know). I pulled the cluster again after seeing  both the fuel and the temp go all the way over. I matched up the pin identifier page  I had printed off (from the forum here) to the plug I have and it says its for a 72. So I'm not sure what I have ,lol. Anyways I took my meter and verified I had 12 volts on the plug,then  I went to pins 2(red & white) and 10 (white & red). First to 2 and checked it to ground for voltage with the key off, then on. Then check for continuity it both conditions: no reading. The same with pin 10. Then I check for voltage  from pin 4 to pin 2 -nothing  checked same pins for continuity and I had it both with key on or off. The same condition exist for pin 10 also. All of these checks were done with the fuel sensor plugged in. I unplugged the sensor and got the same readings. I then read between 2 and 10 for continuity and I had it (with the sending unit unplugged). I'm  not sure but it sounds like a wire has gone to ground. I tried tracing back the #2 pin & #10 wires to see if any thing  had shorted, found nothing there but  I did find a wire that was hanging loose at the fuse box,behind it the wire's purple in color with orange dashes on it. I couldn't see where it had come from or where it had maybe broke from another point. Ive tried to identify it  by its color from the pages I printed off but nothing matches up.  Does anyone know if there is a color code diagram for the wiring ?I'm not sure what else to do as of  now.

not sure if you already did his or not but, have your old cluster and one at a time trace the circuit along the printed part to the plug area there will be several ones to the gauges that are connected through the circuit those are the positive power  from the key then the other stud from each gauge will be the negative with will go to the sender for each gauge ...oil,water, fuel, they get their ground through the sender for each individually and amount of ground is controlled by the sender to make the gauge read appropriately. you'll need to trace each circuit for both clusters and see if a wire will need swapped in the plug for the new cluster to be correct! i think i had to swap 3 wires? also some sport clusters had the gauges in different locations that could cause issues so that's why i say to trace each circuit one at a time and make a diagram to refer to as it can get mind boggling at times  

I hear ya , I found a lot of my trouble with the dash lights is the twist sockets. I pulled all of them and cleaned the contacts and adjusted them to put more pressure on the contact foil and they are working now.  My issue with my temp fuel gauge is the same with either cluster I put in. Plus I keep blowing the rear passenger tail light bulb every so often. Im sure I have a ground issue  I just don't know where. I guess Ill start disconnecting  grounds and see what happens with the fuel/temp guage.

I have a similar issue with my '76 Montego with standard cluster.  At first, I thought maybe my car was running hot.  A couple of summers ago, I noticed my temp gauge creeping up.  But, I wasn't having any other typical issues of a car running hot.  Then, one day I noticed that every time my temp gauge would peg out, my fuel gauge was pegging out at the same time.  It's very intermittent, and only lasts for maybe 5 - 10 minutes when it does happen.  Not enough for me to mess with.  I probably just need to add some reliable mechanical gauges under the dash for now.

RPM will differ with axle ratio's. With 22-25 I'd guess you had around a 3.00 ratio?