Rallye Instrument cluster voltage limiter - 68 Barracuda

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Traxfish

Traxfish

Convertible Cruiser
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I recently did reworking of the gauge cluster to replace lights in my 1968 Barracuda, and replace both of the circuit boards with ones from Classic Industries.
Everything worked fine for a while after, until the temperature, oil pressure, and fuel gauges started going strait to max travel with the ignition on.
Then I heard an electrical pop with a puff of smoke from behind the dash and now the fuel gauge doesn't work, the oil pressure seems to be working fine, and the temperature gauge underreporting. There is also an issue where the Ammeter will drop, wave around, make a "tick" noise, then return to normal which I suspect is related. The lights will dim and flicker along with this but I couldn't read a significant drop in voltage on the battery with a multimeter.
From my reading around this forum and the service manual it is probably the instrument cluster voltage limiter. The only problem is the service manual doesn't identify the limiter for barracudas, only valiants, so I am not sure which component the voltage limiter is. Looking for limiters online match the Valiant's diagram, but I suspect the limiter on rallye dashes was completely different. Is this circled item in the inserted image the voltage limiter?

Whatisthis.jpg
 
the voltage limiter is built into the fuel gauge the circled item is a condenser it’s purpose is to keep the reference voltage stable and noise suppression
 
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Traxfish said:
I recently did reworking of the gauge cluster to replace lights in my 1968 Barracuda, and replace both of the circuit boards with ones from Classic Industries.
Everything worked fine for a while after, until the temperature, oil pressure, and fuel gauges started going strait to max travel with the ignition on.
Then I heard an electrical pop with a puff of smoke from behind the dash and now the fuel gauge doesn't work, the oil pressure seems to be working fine, and the temperature gauge underreporting. There is also an issue where the Ammeter will drop, wave around, make a "tick" noise, then return to normal which I suspect is related. The lights will dim and flicker along with this but I couldn't read a significant drop in voltage on the battery with a multimeter.
From my reading around this forum and the service manual it is probably the instrument cluster voltage limiter. The only problem is the service manual doesn't identify the limiter for barracudas, only valiants, so I am not sure which component the voltage limiter is. Looking for limiters online match the Valiant's diagram, but I suspect the limiter on rallye dashes was completely different. Is this circled item in the inserted image the voltage limiter?

View attachment 1715958484
Click to expand...
The voltage limiter for the Rally gauge cluster in my 68 Barracuda is inside of the fuel gauge.

If the voltage limiter stuck and sent a full 12v to the gauges, those gauges are now fried. With the exception of the amp meter gauge. If the needle on that one is moving around the car has an electrical short, disconnect the battery till you figure that out or the damage may multiply.

The component that you circled is a condenser, used to take static out of the circuit that may be audible on an AM radio frequency.

There is an aftermarket digital voltage limiter, I installed one on my car. Will look for a link and post it.
 
my68barracuda said:
The voltage limiter for the Rally gauge cluster in my 68 Barracuda is inside of the fuel gauge.

If the voltage limiter stuck and sent a full 12v to the gauges, those gauges are now fried. With the exception of the amp meter gauge. If the needle on that one is moving around the car has an electrical short, disconnect the battery till you figure that out or the damage may multiply.

The component that you circled is a condenser, used to take static out of the circuit that may be audible on an AM radio frequency.

There is an aftermarket digital voltage limiter, I installed one on my car. Will look for a link and post it.
Click to expand...

Digital voltage limiter

RTE limiter - rte (rt-eng.com)

there is a special instruction section for installing a RTE digital limiter to a Rally Dash that has the OE voltage limiter in the fuel gauge.
 
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The circled item is a radio noise supression cap, as the original limiter clicked rapidly off/ on similar to a turn flasher.

You may well have damaged/ killed your gauges.
 
67Dart273 said:
The circled item is a radio noise supression cap, as the original limiter clicked rapidly off/ on similar to a turn flasher.

You may well have damaged/ killed your gauges.
Click to expand...
Could you explain how exactly I killed them so I know in the future?

With the suggestion that the original gauges are now fried than I need to start considering replacement options. I'm guessing that installing a new digital regulator as above will not fix them and will need to source replacement ones or look into replacing the whole dash with aftermarket gauge kits.
 
Traxfish said:
Could you explain how exactly I killed them so I know in the future?
Click to expand...
Traxfish said:
until the temperature, oil pressure, and fuel gauges started going strait to max travel with the ignition on.
Click to expand...
Two possiblilities:
The gages got power continuously (approx 12 Volts with engine off, 14 Volts running)
or
The wires from the gages to the sending units got grounded.

here's how the gages and sender work.
Thermal-Electric Gauges (Session 227) from the 1966 Master Technician's Service Conference

And the filmstrip that goes with that, along with a pdf version of the booklet at
Browse MTSC by Model Year – 1966 – MyMopar

No idea why your FSM doesn't have the Rally cluster. I'm pretty sure the Plymouth '68 FSM does. The '67 does not. Dodge '68 I don't know.

First test I suggest is check each gage's resistance.
Gauge Cluster Issues/IVR

If you set up a live test of the IVR on a bench the output voltage will look something like this on a 0 to 8 V scale.
Gauge Cluster Issues/IVR
Scroll up in that thread to see the resistors used to simulate the sending units.

A lot of good info in this thread as well. Redfish knows this stuff.
Bench testing rally gauges

Here's a pdf version of the factory wiring diagram by @1969383S
https://www.forabodiesonly.com/mopar/attachments/68-barracuda-factory-wiring-rev-2-pdf.1715189875/
 
Mattax said:
No idea why your FSM doesn't have the Rally cluster. I'm pretty sure the Plymouth '68 FSM does. The '67 does not. Dodge '68 I don't know.
Click to expand...

I'm referencing the Barracuda instrument panel wiring diagram in the 68 Plymouth service manual (8-112 & 8-113), where it didn't show a voltage limiter while the Valiant wiring diagram does. That was the source of my confusion. Now knowing it's internal to the fuel gauge explains that.

Thanks for the help, I'll read through these links.
 
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