Yet another fuel gauge thread...but different

[bigmanjbmopar]

There is a +5 vdc signal (voltage) to all the guages and the fuel sending unit is basically a resistor and as the arm moves back and forth that changes the voltage of the 5 volts increasing or decreasing that is what you see on the actual gauge. if the wire that goes out to the sending unit is worn out or corroded it will raise the resistance or in some cases lower the resistance causing a no read or low read etc. that's why people say get a new piece of wire and run it from the gauge to the unit and then try it. oem gauges were very slow in reading fas changes to the sending unit arm so don't expect it to read fast.

 

[Qbrozen]

Maybe my post wasn't clear. Should I be getting a signal at the cluster coming from the fuel gauge pin? Folks say to disconnect the wire from the sender and test it there. I did and got nothing. Also nothing at the temp sender. I replaced the voltage reducer on the dash with the solid state unit, but nothing changed. Today, I pulled the gauges again and put a test light on the pin that connects to the blue wire going to the fuel sender but no light. Is that an indication that the gauge is bad? Or is it a fault in the circuit board?

 

[bigmanjbmopar]

No thats not how it works read my post and trybto understand just like a light dimmer the knob is the sending unit adbyou turn it the gauge or lamp goes full or bright or empty or dim hopefully this makes sense?

 

[Qbrozen]

Yes, i do understand what you are saying,but the 5v has to get to the sending unit in order for it to "dim" it, correct? So what does no juice at the fuel gauge pin on the gauge harness tell me?

 

[miller]

Might be looking at a bad circuit board. First thing you might look at is, the condition of the pins themselves on the board. Check with an ohm meter. They can corrode where they fasten to the board, or come loose.
Also look the board over...for burns, or broken connections. Also, look at the gauge lights sockets...with them in place (must be), they make part of the circuit on the board. If their corroded...no contact.

 

[Qbrozen]

Whoa. Really? That could be quite the tip. I have a couple of bulbs with broke bases that aren't making contact.

 

[bigmanjbmopar]

Voltage regulator is bad if you dont have 5 vdc at any if the pins or you have broken circuit traces or broken pins most likely regulator. Make sure you have feed voltage to the pins i want to say pin 7 or 8 is the feeds from the fuse panel

 

[miller]

I have a couple of bulbs with broke bases that aren't making contact.

Possible. Simple to remove the bulb bases, and look at the contacts built into the circuit board. On my 64, contact 'plate' is separated at each bulb location, only connected by the bulb socket. Of course, the sockets need to be in good shape, too.

 

[CoronetDarter]

Latest update: With 3/4 tank of gas, gauge reads about 1/4. I replaced the 8 ga wire with an OEM-style ground strap. At the sending unit post, reads 34 ohms. Seems a little high for 3/4 tank, but its an aftermarket replacement sending unit. At the connector behind the kick panel, wire reads 37 ohms on both sides of the connector. A home run wire from the sending unit reads the same 37 ohms. So I'm now looking at the gauge or the PCB as the culprit. Man, I hate removing the gauge cluster.

 

[bigmanjbmopar]

Cant remember if you said your gauge was original? Standard cluster?

 

[CoronetDarter]

Cant remember if you said your gauge was original? Standard cluster?

Yes, OEM gauge, standard cluster.
After doing more research last night I found an article on grounding the dash. Before pulling the cluster I need to first check my dash grounds. During the resto the dash was removed, blasted and painted. In my quest for the perfectly restored dash, I may have painted all the attaching points to the body.
Some additional information: I converted the ammeter to a voltmeter by changing out the guts and attaching to the OEM face plate. Ran the + to switched power at the fuse panel, grounded it to a screw on the dash. The voltmeter twitches during startup but doesn't work. (yes, the charging system works). Added a OEM style tach from Classic Industries, to the cluster in place of the original clock . The tach swings wildly when cruising; it's almost useless as a RPM gauge.
The temp gauge seems to work fine.

 

[CoronetDarter]

Is POR15 a poor conductor? I'm asking because I painted the interior with the POR, including where the dash frame ears attach behind the kick panels.

 

[bigmanjbmopar]

The OE gauges can be adjusted/calibrated manually there are cogs on each side E/F which will allow you to make adjustments to match your sending unit the new gauges sold now do not have this and have to work imwith newer sending units

 

[CoronetDarter]

Thanks Bigman. That could be the answer I'm looking for.

 

[SureGrip]

Is POR15 a poor conductor? I'm asking because I painted the interior with the POR, including where the dash frame ears attach behind the kick panels.

I would try to get at least one point clear of any coating (dash frame and body) to make sure you have a good chassis ground.

You need to start at the beginning and make sure you have a good ground, then make sure you have a good 5vdc source, as others said, make sure the board is complete and ALL contacts are clean.

Just an FYI to anyone wanting to bench test their stuff...most cell phone chargers (plug into the wall style) have close to a 5vdc output...just clip off the end and strip back the wires.

 

[bigmanjbmopar]

I used a drained 12 vdc battery from a drill before too even some plug in transformers for rechargeable devices and the like.

 

[CoronetDarter]

So, pulled the dash cluster today. Using jumpers, measured resistance at the fuel gauge studs - still 37 ohms.
At tachman.com, it instructs to test the resistance across the fuel gauge studs, should be 10 ohms +/-. My gauge reads 13; 30% delta. So I'm now leaning towards the gauge being the issue.
Also, during the resto I swapped out the ammeter with voltmeter guts behind the OEM face plate. It's never worked. With the cluster out I applied 12 V to the gauge and nothing. At this point I'm really thinking about sending the cluster out to be restored with a voltmeter swap. This site has listed some strong recommendations:
Instrument Specialties
JC Auto Restorations
D&M/Tachman
Performance Car Graphics
All of them have gotten good reviews, leaning towards JC because they're west coast, and Instrument Specialties because they have a strong rep.

 

[bigmanjbmopar]

Pull the gauge and apply 5 vdc -/+ to the studs wait a few seconds to see if the needle moves it should slowly go to full to the cog set point the empty set point is where it sits with no power. if it does this the gauge is good. Check the circuit board are there any broken or burnt traces? if not replace the limiter the rectangle can. or replaced the board with a new one with solid state limiter. then try all of it again. the old gauge is mechanical and they rarely go bad, out of adjustment but rarely bad. Just trying to save you some money and time.

 

[CoronetDarter]

I will test the gauge with the 5 vdc.
I neglected to mention earlier that the original 5 vdc limiter was replaced with a RTE digital limiter back in 2014.

 

[SureGrip]

EDIT to my previous post.

The USB charger puts out 12VDC at 5amps just like the factory regulator on the dash....not 5VDC like I posted, ....sorry for any confusion!