Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
I'm having troubles with my fuel and temp gauges for my 1966 Plymouth Fury and want to make sure I have a good ground. The voltage limiter works fine and I installed a new temp sending unit. Here's some inconsistant tests I ran:
A. I tried the shop manual's bench test (disconnected and removed instrument cluster): 1. Hooked up 12 Volts to the cluster "I" bolt 2. Connected instrument cluster housing to battery negative terminal 3. Connected cluster housing to fuel gauge "S" bolt RESULT- fuel gauge did NOT move
B. Alternate bench test (disconnected and removed instrument cluster): 1. Hooked up 12 Volts to the cluster "I" bolt 2. Connected fuel gauge "S" bolt directly to battery negative terminal RESULT- fuel gauge reads FULL! (as it should)
Question 1: Why didn't test A) work? The gauges are bolted to the cluster housing. The housing is metal and I sanded it a little before clamping onto it.
Question 2: How do you make sure the installed instrument cluster is grounded? I know that by screwing it into the dash should establish a ground, but is there a way to install a discreet ground wire? Thanks for any suggestions!
Joined: Sun Feb 26 2006, 08:46PM
Location: Kingston,Ontario
Posts: 5622
PUTTING 12 VOLTS TO THE FUEL GAUGE CAN DAMAGE IT!! It only runs on 5 volts. In test 3,the guage will not move since it is not getting a reading from the sender. I tested my guage with a spare sending unit,and went through the voltage limiter and correct circuit order..
The instrument panel is grounded to the dash since everything is metal. I assume you checked the fuse for the guages,and checked the bulkhead connector for continuitity. Hope this helps. BTW,did I see your car at the Long branch show?
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
sorry I wasn't at the Long branch show. Where is the fuse for the gauges? I didn't see one in the wiring diagram from the shop manual. Are you sure a fuse goes to these? The "I" bolt is for the incoming 12 V power. The fuel gauge has a voltage limiter inside it which drops the voltage down to 5 V. In my alternate bench test, hooking up the "S" bolt to ground basically gives zero resistance, so the gauge registers full. I did this for ~1 sec so as to not fry the gauge.
By the way, how do I modify the original thread? I can't correct some errors. The smiley face should be test .
Joined: Sun Feb 26 2006, 08:46PM
Location: Kingston,Ontario
Posts: 5622
Sorry,I got the instument panel lamps fuse mixed up.My bad. To modify the original thread just click on edit (between REPORT and QUOTE on the right side of the screen and edit away even on the title if needed.
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
Thanks for the tip on editing! I have good contintuity from the sending units to the wires that plug into the instrument cluster. I have good continuity on my circuit board. It bothers me that bench test A completely failed. I'm missing a contact somewhere. If the gauges don't have ground as a reference, then they won't work. The fuel gauge actually edges up to "empty" on a full tank of gas, but the temp gauge doesn't move at all.
Joined: Sun Feb 26 2006, 08:46PM
Location: Kingston,Ontario
Posts: 5622
Didd you test the ohms from the fuel sending unit?? Full tank should read 12-19 ohms and empty tank should read up to 75 ohms. based on what you are saying I am suspecting the voltage limiter. You can get an electronic limiter that well work with your guages.
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
I'm confident it is NOT the voltage limiter. I bought a NOS gauge and my bench test B worked fine. I can't figure out why bench test A didn't work. It means that the cluster housing is not conducting.
Joined: Fri Oct 07 2005, 12:03PM
Location: Central Ky.
Posts: 1575
If you really think it's a ground issue find a screw going into the Circuit board that hit's a ground trace & use a wire/ring connector under & find a good ground point to the metal dash.
Circuit board should ground to the Aluminum cluster Housing & then to the metal dash through the mounting screws. <span class='smallblacktext'>[ Edited Fri Jul 02 2010, 06:28AM ]</span>
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
Thanks for the tip. Would you say the (philips head) screw located in the center of this instrument circuit board (in between the light bulbs and above the alternator bolts should go to ground? I'll have to add the image of this circuit board after I cleaned it up. I suspect that maybe you are right, perhaps the circuit board is not properly contacting the housing, which provides the ground. <span class='smallblacktext'>[ Edited Fri Jul 02 2010, 01:15PM ]</span>
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