66 Barracuda gauge problems

[AussiePlymouths]

Gday everyone,
Posting from Australia.

I have a '66 Barracuda imported here 20 years ago. Poor thing has had a rough, unloved life, but it's a formula S and very few of those here so I thought it was worth saving.
So 20 years of life gets in the way of getting this car up and running but finally 2025 is THE YEAR! (I hope).

The electrical wiring did not enjoy all of those years of sitting. Most connections badly needed cleaning, that huge connector on the firewall was in a terrible state and we spent a long time cleaning, cleaning and more cleaning. so finally all is good except we can't get readings at the fuel and temp gauges. I put a new fuel tank and sender (and ground strap), and new temp sender and new oil pressure sender in, all from Rockauto.

My electrical problem is that I believe that the 5 volt voltage limiter in the fuel gauge is burnt out. Temp and fuel gauges are not reading.
Oil Pressure is reading but my wiring diagram shows that the oil pressure guge feeds from sender so I assume that the voltage limiter controls just temp and fuel. Am I correct please?

When we a had the gauge pod unscewed from the dash, but still wired up, we grounded the third post of the fuel gauge through a circuit tester and the tester lit up in slow blinks, does that sound correct ?

Just wondering if anyone has had a similar problem and found a solution, please?

TIA for your input
Gary

 

[Syleng1]

Yes I have on my 66 Barracuda cluster.
I ended up wiring in a separate IVR to run my cluster and it works great. You do have to disable the one inside your fuel gauge. I’m sorry I don’t have photos this second but use the search feature for IVR and there are posts about it including mine to help you.
PM direct and I can send over what I have at a later date. Trying to get off to work now.
Syleng1

 

[Syleng1]

Okay I found them quickly:

 

[Syleng1]

The new IVR was for like a replacement 72-76 dash cluster for my 72 demon but electronic not factory mechanical.
Black wires were for the fuel gauge studs and the red wire was key “on.”
I bought the electronic IVR on eBay.
Syleng1

 

[Mattax]

My electrical problem is that I believe that the 5 volt voltage limiter in the fuel gauge is burnt out. Temp and fuel gauges are not reading.
Oil Pressure is reading but my wiring diagram shows that the oil pressure guge feeds from sender so I assume that the voltage limiter controls just temp and fuel. Am I correct please?

Oil pressure is also a "5 V" gage.
What diagram are you looking at? '66 Plymouth Service Manual?

When we a had the gauge pod unscewed from the dash, but still wired up, we grounded the third post of the fuel gauge through a circuit tester and the tester lit up in slow blinks, does that sound correct ?

Grounding is the last thing you'ld want to do for testing. If you must, keep it brief. That's a way to burn out the resistance (heating) wires.
I'll have to look at the gage back again but the terminals are feed (12 V), then connection going to fuel sender and connection to the board for the other '5V' gages

 

[Mattax]

The 5 volt number seems to come from old tech bulletins. For example page 3
Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference

It doesn't say the IVR puts out an average of 5 Volts. It says the effect is the same as steady 5 Volts. Good info for testing the gage but not directly useful for verifying the IVR. When I tested the IVR in the '67 rally cluster you can see the voltmeter needle swings practicaly to full scale (8 Volts). Its not a true square wave or perfectly consistant in frequency. (link to video below)

Rally dash gauge voltage. 5v or 6v nominal?

I have a 68 Barracuda in Australia & I am fitting a variable DC supply to my rally dash gauges to fix a fluctuating reading problem. I have been told that gauge design from the 6v days continued & the remedy was to just add the vibrator contact system to clip the 12 volts down to 6volts. I also...

www.forabodiesonly.com

Scroll through that thread ^^^^^^
You'll see several ways the gage and sending units can be checked.
Begin with a simple check of resistance in the gage and the sending units
Then you can input a 3 to 6 votls of dry cell power
and/or hook up some resistors or a potentiameter to simulate the range of resistances for the sender and input battery power through the IVR.

pdf version of the Master Tech Conference posted at MyMopar.com

http://www.mymopar.com/downloads/mtsc/227.pdf
as is the filmstrip in larger format

 

[Syleng1]

Mattax- if you put a volt meter on the gauges while in the car and wired up the factory unit pulsed. It came “on” then the little bi- metal strip heated up or “tripped” and the system goes dead and it recovers rather fast then does it again.
That’s how it got the roughly 5vdc.
Mine did not do that any longer. I had a good gauge but it was in rough shape to verify it. I went to the electronic and my gauges are very happy now. Quick to respond and smoother than original.
Syleng1

 

[Mattax]

Mattax- if you put a volt meter on the gauges while in the car and wired up the factory unit pulsed. It came “on” then the little bi- metal strip heated up or “tripped” and the system goes dead and it recovers rather fast then does it again.
That’s how it got the roughly 5vdc.
Mine did not do that any longer. I had a good gauge but it was in rough shape to verify it. I went to the electronic and my gauges are very happy now. Quick to respond and smoother than original.
Syleng1

I post a video in the linked thread showing the pulsing using an analog 0-8 V meter.

 

[AussiePlymouths]

Yes I have on my 66 Barracuda cluster.
I ended up wiring in a separate IVR to run my cluster and it works great. You do have to disable the one inside your fuel gauge. I’m sorry I don’t have photos this second but use the search feature for IVR and there are posts about it including mine to help you.
PM direct and I can send over what I have at a later date. Trying to get off to work now.
Syleng1

Thank you so much, That is exactly the answer that I was wanting.
Very much appreciated.

Okay I found them quickly:View attachment 1716365973View attachment 1716365974View attachment 1716365975View attachment 1716365976View attachment 1716365977View attachment 1716365978View attachment 1716365979View attachment 1716365980

Thank you for posting those poics, and your explanation and the tip to look on Ebay, You have been a great help.

 

[AussiePlymouths]

The 5 volt number seems to come from old tech bulletins. For example page 3
Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference

It doesn't say the IVR puts out an average of 5 Volts. It says the effect is the same as steady 5 Volts. Good info for testing the gage but not directly usefuli for verifying the IVR. When I tested the IVR in the '67 rally cluster you can see the voltmeter needle swings practicaly to full scale (8 Volts). Its not a true square wave or perfectly consistant in frequency. (link to video below)

http://[URL]https://www.forabodieso...ltage-5v-or-6v-nominal.514919/post-1973864067

[/URL]
Scroll through that thread ^^^^^^
You'll see several ways the gage and sending units can be checked.
Begin with a simple check of resistance in the gage and the sending units
Then you can input a 3 to 6 votls of dry cell power
and/or hook up some resistors or a potentiameter to simulate the range of resistances for the sender and input battery power through the IVR.

pdf version of the Master Tech Conference posted at MyMopar.com

http://www.mymopar.com/downloads/mtsc/227.pdf
as is the filmstrip in larger format

Thank you for taking the time to reply and for posting those links.
Unfortunately I am not electrically minded and I thought that the oil pressure gauge, being on a seperate board, may not have been 5v.

I still can't see how the 5v power gets from the fuel gauge to the other board _ what am I missing there please?


Yes I have a Plymouth shop manual thanks, and I studied the wiring diagrams, tryting to nut it out.

I am wondering now if my Voltage limiter may in fact be working.
Because we did get that flash, pause, flash, pause on the circuit tester light.

I will look through those links that you kindly posted tomorrow, they may help me to understand.

Not to "muddy the waters" so to speak, but this car has an Aussie 318 in it. The Aussie Valiants used VDO gauges, and when I couldn't get a reading at first I thought that it may have been the senders on the Aussie engine being incompatable with the factory Barracuda gauges. that's why I bought new senders from Rockauto. Unfortunately the senders made no difference.

Thank you again for your help.

 

[AussiePlymouths]

Okay I found them quickly:View attachment 1716365973View attachment 1716365974View attachment 1716365975View attachment 1716365976View attachment 1716365977View attachment 1716365978View attachment 1716365979View attachment 1716365980

Thank you for all of those images.
I take it that those are brand new circuit boards?
very nice

 

[cudamark]

The IVR in the fuel gauge runs all three gauges....oil, temp, and fuel. The power for the oil gauge runs through the dash harness to the other circuit board. If your oil gauge is working, the IVR is working also (although I would change to the solid state one anyway to keep from frying the gauges should the factory IVR stick on full power). Chances are, you have a bad connection, loose pin or nut, or broken trace on the circuit board. a simple test light should be able to track that power loss problem. Start at the IVR output on the fuel gauge and work your way to the post on the other gauges.

 

[Mattax]

Unfortunately I am not electrically minded and I thought that the oil pressure gauge, being on a seperate board, may not have been 5v.

I still can't see how the 5v power gets from the fuel gauge to the other board _ what am I missing there please?


Yes I have a Plymouth shop manual thanks, and I studied the wiring diagrams, tryting to nut it out.

The same Master Tech Conference has sessions on how to read the wiring diagrams.

Lets look at the '66 Plymouth FSM.

The dashed lines represent the instrument panel.
Wires are identified by a code. G is for Gage. Number is the circuit and a letter, if present, is a branch.
In the key is the wire color and SAE wire gage. So G1 is 18 gage black, and my guess is that is the power supply from the key switch. Lets look.

Yes it its.
How do we read this? The circles represent junctions. Usually they are solid circles but for whatever reason in this case the welded junctions are larger open circles. Wire G1 joins wire Q2 coming from the ignition switch.
J1 is the feed into the key switch. Its always hot and by accepted convention the connections are marked Batt or B or Battery. Don't let this fool you into thinking it comes direct from the battery. It comes from a junction joining the battery (wire R6A) and the alternator output power (wire R6) to the main feeds. Lets color these in.

When the key is in Run, there is power at the switched accessory terminal as well as the ignition run terminal.
Lets color those in. (even better sometimes is to redraw the circuits we're interested in on apiece of paper)

Now lets go back to the instrument panel connector.
G1 brings power in. We call it 12 Volts (even though its really close to 14.5 V when the engine is running)

The solid dots represent the connected terminals.
12 Volts is available at the Fuel gage. Inside the gage it connects to the IVR.
From the IVR reduced (pulsating) power is available to the fuel gage resistance wire.
Via the circuit board it the the IVR power is available to the termperature gage.
It seems the IVR feed to the oil gage on the other board is incorrectly marked "Oil and Temperature Gage". I would guess that confused things.
The only thing wire G3 feeds is the oil pressure gage.

 

[Mattax]

Here's how the 66 Barracuda main circuits look when the diagram is redrawn in to a schematic just focused on them.

 

[AussiePlymouths]

The same Master Tech Conference has sessions on how to read the wiring diagrams.

Lets look at the '66 Plymouth FSM.
View attachment 1716367055

The dashed lines represent the instrument panel.
Wires are identified by a code. G is for Gage. Number is the circuit and a letter, if present, is a branch.
In the key is the wire color and SAE wire gage. So G1 is 18 gage black, and my guess is that is the power supply from the key switch. Lets look.
View attachment 1716367057
Yes it its.
How do we read this? The circles represent junctions. Usually they are solid circles but for whatever reason in this case the welded junctions are larger open circles. Wire G1 joins wire Q2 coming from the ignition switch.
J1 is the feed into the key switch. Its always hot and by accepted convention the connections are marked Batt or B or Battery. Don't let this fool you into thinking it comes direct from the battery. It comes from a junction joining the battery (wire R6A) and the alternator output power (wire R6) to the main feeds. Lets color these in.
View attachment 1716367061

When the key is in Run, there is power at the switched accessory terminal as well as the ignition run terminal.
Lets color those in. (even better sometimes is to redraw the circuits we're interested in on apiece of paper)
View attachment 1716367064

Now lets go back to the instrument panel connector.
G1 brings power in. We call it 12 Volts (even though its really close to 14.5 V when the engine is running)
View attachment 1716367077

The solid dots represent the connected terminals.
12 Volts is available at the Fuel gage. Inside the gage it connects to the IVR.
From the IVR reduced (pulsating) power is available to the fuel gage resistance wire.
Via the circuit board it the the IVR power is available to the termperature gage.
It seems the IVR feed to the oil gage on the other board is incorrectly marked "Oil and Temperature Gage". I would guess that confused things.
The only thing wire G3 feeds is the oil pressure gage.
View attachment 1716367078

Thank you for all of your help, I am learning so much from your posts !

 

[AussiePlymouths]

Here's how the 66 Barracuda main circuits look when the diagram is redrawn in to a schematic just focused on them.
View attachment 1716367083

You have been very helpful, thank you for your trouble!

 

[AussiePlymouths]

The IVR in the fuel gauge runs all three gauges....oil, temp, and fuel. The power for the oil gauge runs through the dash harness to the other circuit board. If your oil gauge is working, the IVR is working also (although I would change to the solid state one anyway to keep from frying the gauges should the factory IVR stick on full power). Chances are, you have a bad connection, loose pin or nut, or broken trace on the circuit board. a simple test light should be able to track that power loss problem. Start at the IVR output on the fuel gauge and work your way to the post on the other gauges.

Thank you for your input. I have been puzzled as to why theoil pressure gauge is working but not the other 2.

 

[Syleng1]

Thank you for all of those images.
I take it that those are brand new circuit boards?
very nice

Yes. They were brand new but not NOS. A company in Canada was producing them and selling them on EBay.