Joined: Fri Oct 07 2005, 12:03PM
Location: Central Ky.
Posts: 1575
I cant tell, the pic is too small. What you want is to follow the traces & see which trace is ground & has a screw in it. that big one might be but I can't see the traces.
Here's a tip, take the board off & clean all the copper traces where the nuts sit & such with say 0000 steel wool . Just make sure everything is clean so it makes connections. from your pic the left is the Fuel gauge & right is the Temp I'm guessing with Ammeter down in the middle.
If the board gets cleaned & makes good with the Housing it should get a good ground. check it with a meter for ground.
Joined: Fri Oct 07 2005, 12:03PM
Location: Central Ky.
Posts: 1575
YES! Now that I can see the traces it sure is. Light voltage comes in on the left pin flows through each bulb & then to ground. course that's just ground for the 2 lights. A wire there would ground the cluster housing better since the screw goes into the housing. Just ground to the meatal dash frame somewhere.
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
I took the instrument cluster apart for the 100th time and checked that the screw (Circled in red) threaded into the housing nicely and sanded the contact points where the housing and dashboard meet and screw together. I can't check the fuel sending unit because I can't drop down my tank, but I did make sure the tank is full and there is good continuity for both the temperature and fuel sending wires.
Here are 4 tests that I ran recently:
I. With the cluster in the dash, I disconnected the temperature sending unit wire. A. Connected the battery ground to the dangling temperature sending unit wire. Gauge reads "HOT"(good result!) when ignition turned on. NOTE: this was done for just a second, so I wouldn't fry the temperature gauge. B. Connected the battery ground to a 21 Ohm resistor. The other side of the resistor was then connected to the dangling temperature sending unit wire. Temp gauge reads "COLD" (should read 1/2 way). C. Switched to a 10 Ohm resistor. The Temp gauge reads "COLD" (should read "HOT").
II. Pulled the cluster out of the dash and disconnected the multi (4-prong) connector from the back of the circuit board. I kept the alternator wires connected. Used an alligator clip to connect the battery positive post to the Fuel Gauge "I" post. Connected the battery negative post to a 21 Ohm resistor. The other side of the resistor was connected to the Fuel gauge "S" post. RESULT: Fuel gauge reads "FULL" (should read 1/2 full according to some web sites).
So what is going on? It appears the gauges function, the sending unit wires have continuity, the circuit board has good continuity, but the gauges have a much narrower response to resistance than what they should. Any suggestions would be GREATLY appreciated! <span class='smallblacktext'>[ Edited Sun Jul 11 2010, 09:15AM ]</span>
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
Thanks to the bozos who engineered a voltage limiter INSIDE the fuel gauge. This is the crappiest design that makes for a HUGE headache. I bought a NOS fuel level gauge on E-bay and my gauges still don't work. But, I think I've discovered the problem. I've disassembled the fuel level gauge by drilling out the 2 rivets that hold on the face plate:
Here's how it (SHOULD) work. The voltage limiter is circled in blue. It takes 12 Volts from the "I" post, and sends current to the heating coil contact via the white wire. The contact opens (stops current flow) and closes (allows current flow) to produce an average of 5 Volts, which is sent to the "A" post via the coiled band (note the flimsy gound wire indicated in green). The "A" post then sends this averaged current (via a coiled band) to the fuel level gauge on the left. The "S" post reads a resistance from ground from the sending unit. The 5 Volts and resistance from ground causes the gauge arm to swing anywhere from empty to full. I noticed that when I applied 12 V to the "I" post, the heating coil contact would open and not allow the fuel gauge coil on the left to heat up enough to cause the arm to swing. At risk of frying the wires, I physically held the contact closed (ouch, hot wire!) and the gauge arm started to move. This indicated to me that the gauge functioned properly, and the voltage limiter works, but does NOT work correctly! Following the procedure from the shop manual to test a varying current at the "A" post (swinging 1-12 volts) was not enough to diagnose this problem. The following post is how to perform a better test and my recommendation.
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
Here is a better and safer bench test of the fuel level gauge which will not fry your component and does not require taking the fuel level gauge apart:
First, hook up 4 charged D batteries in series and test the voltage with a multimeter:
This is close enough to the 5 Volts we need at the "A" post. Next, tape a wire to the positive battery terminal and clip it to the "A" post. Then tape a wire to the negative battery terminal and clip it to a 1/2 Watt, 5% tolerance resistor (10, 22, 47, or 75 Ohm) bought from Radio Shack. Clip the other side of the resistor to the "S" post. NOTE: I found it is crucial to clip as close to the resistor as possible, or this doesn't work correctly!
Full setup, with resistor circled in yellow (contact at + post not good):
Here's my test with a 47 ohm resistor, making sure the contacts are tight:
Here's my test with a 22 ohm resistor, making sure the contacts are tight:
Some notes: The 10 Ohm resistor should get a "full" reading. The 22 Ohm resistor should get a 1/2 full reading. The 47 Ohm resistor should get a 1/4 full reading. The 75 Ohm resistor should get an "empty" reading.
So in this bench test, the gauge works perfectly fine with a STEADY 5 Volts applied to the "A" post. The test tells nothing about the voltage limiter itself.
My Recommendation: Replace the voltage limiter with a modern (STEADY) 5 V voltage limiter. I'll show how this works once I get it done on my car and the results. Wish me luck and I hope this helped other people! <span class='smallblacktext'>[ Edited Wed Jul 14 2010, 05:42AM ]</span>
Joined: Fri Jun 11 2010, 04:49AM
Location: Albany, NY
Posts: 48
Update:
I've plated the circuit board with liquid tin (MG chemicals) to prevent corrosion after cleaning the circuit board. Next I installed a modern voltage limiter with heat sink and a capacitor as described here: http://www.allpar.com/history/mopar/electrical2.html Items bought: 1. Liquid Tin solution (from Allied Electronics) 2. IC Pos volt reg 5V 1.5 A to 220-3 (Digi-Key no. 296-13996-5-ND) 3. Heatsink PWR HORZ black to-220 (Digi-Key no. 294-1067-ND) 4. CAP 100V 10UF ELECT AXIAL (Digi-Key no. 4254PHCT-ND) 5. #6 � 1/2" pan head phillips Self-drilling Zinc screws 6. Heat shrink tubing 7. Ring connectors 8. 20-Gauge copper wire 9. acid-free solder
Note: The electonic components from Digi-Key are really cheap, you pay more in Shipping and handling. I recommend buying extra quantities as a backup. The heatsink I bought is HUGE and I would recommend buying a smaller version. It makes it hard to install the instrument cluster back into the dash board. If anyone buys a few smaller ones, please ship one to me. I don't want to pay $8 S/H for a $3.66 item!
Here is what I did which allows you to install a modern voltage limiter without taking the fuel level gauge apart: I created a gap in the circuit board's 12 Volt path. Carefully using a razor blade, I cut out a piece of the copper path between the "I" post and the multiconnector's incoming 12V rivet. This way, the internal voltage limiter gets no juice but you still have access to 12 Volts. It's easier to buy a new (aftermarket) circuit board for $75 (http://www.premiumdashdecals.com/dash_circuit_boards.htm#cbody) then finding a NOS fuel level gauge.
Then I drilled a self-tapping screw into the housing to mount the 5V limiter onto a heatsink. 3 wires were soldered onto the limiter and used heat-shrink tubing to protect the connection. The red wire ran to the 12 Volt path (near the multiconnector rivet) for incoming voltage, the green wire to ground (bolt near the light bulbs) and black wire to the "A" post. A capacitor (Blue doohickey) was soldered to two wires, which were connect to ground (negative side of capacitor!) and the 12 V path (near the multiconnector rivet).
Bench test results: The fuel level gauge works perfectly fine and new voltage limiter provides a steady 5V! Hooking up a 6 V battery to the "I" rivet and ground screw, I read a nice 5V at the A post for both the fuel gauge and temperature gauge. The NOS fuel gauge responds perfectly to the tests perfomed above, but the temp gauge has a retarded response with the needle and is faulty. I will replace this with a NOS temp gauge I bought online.
Further notes: I checked the ground strap on the fuel tank and found it was perfectly fine and gave a 0 Ohm reading with respect to ground. With the fuel tank full, I disconnected the sending unit wire and tested the sending unit bolt with respect to ground and got a reading of 83 Ohms. It should read 10 Ohms! Therefore, my fuel sending unit in the gas tank needs replacement!
Conclusion: This whole oddessy began because neither my fuel level gauge nor temp gauge worked. The first assumption is that the voltage limiter is bad. In my particular case, the two gauges are not working for two separate reasons. The fuel sending unit is bad and the temperature gauge is faulty! I'll have to bring the car in to a shop to fix the fuel sending unit, but I can replace the temp gauge myself. I'm happy that my new voltage limiter works though.