‘66 Barracuda Fuel Gauge Pegged!

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clifftt

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I received my original fuel sender reconditioned by Abbott Instruments in Portland. Wasn’t cheap, but after trying an aftermarket POS, I bit the bullet and it worked great!

Some months later, I started the car and noticed the fuel gauge pegged. Eventually, I found the wire leading to the fuel sending unit had insulation burnt where it contacted the exhaust pipe. Now, with the sender wire disconnected, fuel gauge reads below “E”. But with wire connected and ignition on, it pegs the needle past “F”.

I visually checked for any shorts of the sender wire thru the trunk floor and up the rocker panel, under the sill plate and everything looks fine. (NOTE: When this happened, I was running a SW temp gauge. I reconnected the factory temperature gauge with the factory sensor to check if the temp gauge works, but it does not.) The factory diagram shows the IVR is in the fuel gauge and current feeds the temp gauge which is why I suspect the gauge.

After spending a few hours on this forum and reading countless threads, I’m at the conclusion I need to pull the dash cluster and check out the fuel gauge. Am I moving in the right direction? And if found bad, is the gauge toasted, or is there a chance I can solve the problem by bypassing the IVR with RT-Engineering’s solid state IVR?

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I had a similar issue with 66 Barracuda Fuel gauge - the ivr is in the fuel gauge for that cluster- I will post my pictures.
I removed it and went externally with the RT engineering solid state and some wiring- fixed it. Gauges work faster as well- no warm up time is best way to describe the issue. Keep us posted on your findings. A few posts about this situation on here using search feature.
 
Joe: Looks like you also changed the board while you were at it? That arm looks toasted in your photo.
 
Joe: Looks like you also changed the board while you were at it? That arm looks toasted in your photo.
Board was changed a while back. Not sure of the arm you mean other than the arm for the ivr inside the gauge. Yea! That was toast. I also swapped out the factory tach with the one VansLLC sells. Works good with modern HEI ignition.
 
I'm trying to imagine the effort involved in "visually inspecting" the fuel sender wire throughout the cabin, or end to end. A ohms meter will tell me if there is a problem in the wiring and what the sender is doing. A volts meter will tell me what the limiter is doing. Since you did find the sender wire shorted to the exhaust/whatever I'm going to assume the limiter is toasted. Oil gauge sender wire do the same when its plastic terminal covering disappears and that bare terminal falls to a chassis ground. Oil warning lamp is on a separate switched 12 volt supply so this terminal fault doesn't effect limiter or fuel and temp gauges. Anyway...
A fuel gauge needle is supposed to go to a home position below the 'E' at switch off. If your fuel gauge beam is overheated and has a bow at room temperature the needle no longer travels all the way to home position. So while we dont see your gauge inside or out... it reads good in text. There are ways to test gauges while you have them out. You'll need to clean up there connections anyway. The stamped tin speedy nuts contact only 1 thread of the gauge post. So a rusty post is degraded connection.10-32 hex nuts and internal toothed washers exactly like those on your amp gauge can be had for coins at Home Depot, etc...
You will need to pull the inst' panel to install a solid state gauge voltage regulator such as the RTE unit. You do not need to open the fuel gauge, cut or bend anything there. Lift the fuel gauge from the housing to find a slither of metal attached to its backside. That is the chassis ground path for the internal limiter. Simply cover this with a layer or 2 of electric tape to block the ground/isolate this gauge can (just like 2 post gauges are not grounded to the housing or anything).
Where a switched 12 volt wire serves nothing more than that limiter, take it out of the circuit board harness conntor and route it directly to the add on regulator no matter where you choose to mount it. It dont have to be on the back of the inst' panel. It does need a good ground and will likely ground better mounted anywhere else under the dash. Route the regulators output wire to either fuel gauge or temp gauge. Printed circuit board carries that voltage from one gauges post to the other.
 
Thanks Redfish. I’ll pull the cluster next weekend. Bay Area temperatures this week are crazy hot, has been in the 100’s the last few days! I’ll wait for a cool down, then post what I find.
 
I'm trying to imagine the effort involved in "visually inspecting" the fuel sender wire throughout the cabin, or end to end. A ohms meter will tell me if there is a problem in the wiring and what the sender is doing. A volts meter will tell me what the limiter is doing.

I'm a "nuts and bolts" guy, meaning I can touch it and see it. Electricity is abstract to me. I've taught myself to read these old car schematics, and can sorta use a multimeter, but still lack some fundamentals. Anyways, I really appreciate guys like you where this stuff seems natural. Thank you for replying!
 
Got my RT-E stuff Friday, new boards supposed to be delivered tome Tuesday.
Joe, what’s with the red wire going to your tach? Looks like you cut and changed out the tach?
 
Redfish, I was reading a old thread you helped out Mattax. The TEMP GAUGE ohm reading was supposed to be around 20? My temp gauge is out and on the bench. I read mine
and show no continuity. Fried maybe?

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Redfish, I was reading a old thread you helped out Mattax. The TEMP GAUGE ohm reading was supposed to be around 20? My temp gauge is out and on the bench. I read mine
and show no continuity. Fried maybe?

View attachment 1715587055
Chnage meter to from 200 to 20 ohm scale. Put leads together to see about zero, what resistance is in the leads. There are 2 different fuel gauges, 20 ohms, and 13 ohms. Temp gauge should be 20 ohms plus the leads resistance. Its no so common fro the wire to break away from a post creating open gauge. More common is wire insulation failed, wire shorted to beam. Check resistance from post to can. That should be open.
 
The lowest setting on my meter is 200 ohms. (Rats, I just bought it!)
I checked resistance from each post to can:
“S” to can reads 34.5, “I” is open.
I’d love to look inside this temp gauge but not sure how to take it apart. And if I did get inside, not sure if I’d be able to fix it anyways. I can solder a wire if that’s all it takes.
 
Well, this is cool...tried bench testing the fuel and temp gauges. I rigged up a new, but crappy, Chinese fuel sender to the back of the circuit board, and I can make the fuel gauge read high, low, in the middle,...whatever! But when I move the sending unit wire to the temp gauge, it’s dead. (The fuel sender, after all, is just a big variable resistor, right?)

I can always go back to my SW temp gauge, at least I’ve got my fuel gauge back. But heck, if I’m this far along, I’d like to try to get a working factory temp gauge in case I, or any future owner wants to go back to the stock setup.

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Same sender would work the temp gauge so you've pretty much proven it dead.
 
I can see a broken wire inside. It’s pretty fine. I can try to solder together, have nothing to lose.
 
OK that wire is nichrome. Solder wont stick to it. Its yellowish spiral wound fiber insulation was nearly invisible. The black carbon build up makes it look several times its original size. That restricts beam movement like a plaster cast on arm. Try to clean it and it crumbles to look like black pepper, wire shorts to beam (if it hasn't already).
Buy a good used gauge or send that one out for renew.
 
upload_2020-9-7_7-48-37.jpeg

I’ll be posting in the parts wanted section then. Redfish, thanks for all your guidance!

upload_2020-9-7_7-47-54.jpeg
 
Well, totally bummed out!!! I have everything together, although the temp gauge is cooked (still trying to find a replacement). Cluster is back in the dash and also attached an auxiliary ground from the pot metal cluster to the dashboard. I also bought brand new circuit boards and installed.

As stated and shown in post#13, the fuel gauge was tested and working with the cheapie Chinese sender on my bench. But now back in the car, I turn on the ignition and the gauge goes full peg!

I know somewhere, a wire has to be grounding, but I don’t know how to check it. Seems to me with a test light or an ohm meter, I am always going to find continuity, so that test doesn’t make sense to me. And visually checking, I see no problems.

I spent over an hour on YouTube but only see generic ways of testing. With my test light, I See I have current at the fuel sender wire, and have current at the fuse box.
 
Well, totally bummed out!!! I have everything together, although the temp gauge is cooked (still trying to find a replacement). Cluster is back in the dash and also attached an auxiliary ground from the pot metal cluster to the dashboard. I also bought brand new circuit boards and installed.

As stated and shown in post#13, the fuel gauge was tested and working with the cheapie Chinese sender on my bench. But now back in the car, I turn on the ignition and the gauge goes full peg!

I know somewhere, a wire has to be grounding, but I don’t know how to check it. Seems to me with a test light or an ohm meter, I am always going to find continuity, so that test doesn’t make sense to me. And visually checking, I see no problems.

I spent over an hour on YouTube but only see generic ways of testing. With my test light, I See I have current at the fuel sender wire, and have current at the fuse box.
Disconnect the sender wire at the sender and the instrument cluster. Set you meter to ohms and check the wire to ground. If it reads continuity, that wire is shorted.
Quick verification of gauge & sender, use a long wire with alligator clips and hook one end to sender, the other to the fuel gauge. This eliminates the harness wire, gauge should work.
 
You made that simple and I appreciate that. I did not think of those ideas, thanks!
 
You can separate a harness connector behind the left kick panel and test sections of the dark blue sender wire. If the wire is good from that connector to the sender the ohms measurement would be relative to what level of fuel in the tank. If the wire is shorted to ground, zero resistance, I'm thinking other owners have found it shorted in the trunk area.
 
“Disconnect the sender wire at the sender and the instrument cluster. Set you meter to ohms and check the wire to ground. If it reads continuity, that wire is shorted.“
I’m not showing continuity, so rear harness is good.

“You can separate a harness connector behind the left kick panel and test sections of the dark blue sender wire. If the wire is good from that connector to the sender the ohms measurement would be relative to what level of fuel in the tank.“
It is, Redfish, showing 16.5 ohms, that is at the kick panel with the plug disconnected.

But, when I put a probe into the mating connector, the one that goes up into the dash, I get a continuity reading of 35 ohms (battery is disconnected).
This tells me there’s a short in the upper harness, correct?
 
But, when I put a probe into the mating connector, the one that goes up into the dash, I get a continuity reading of 35 ohms (battery is disconnected).
This tells me there’s a short in the upper harness, correct?
No sir, the fuel gauge is 20 ohms. That may have a backward path to ground through a limiter or regulator.
I dont know what you used for a 5 volt power supply at the workbench or what you are using in the car. Far too much power going into a gauge will peg it and look like a short circuit.
If you have RTE regulator, did you disable or isolate the original mechanical limiter?
 
I installed the RT-E regulator and bench tested with a cheap Chinese sender (see my post #13 with a picture). As I moved the sender float, the gauge would move up and down. The back of the fuel gauge has thin dense cardboard to prevent it grounding. It was fit snugly between the posts.

I have the cluster loosened and ready to come out again. I might try what Bob said in post#20, to use a separate wire outside of the car from the sender straight to the gauge to see what happens. I’ll double check to make sure the cardboard is in place behind the fuel gauge, too.
 
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