The instrument panel consists of for round Bezels with six gauges. Besides the normal instruments, there is a standard 6000 RPM tachometer. All instruments are illuminated without the use of the 12V DC light bulbs as in other MOPARS. This system, known as Electroluminescent Lighting (EL) creates a soft uniform glow without objectionable intensity and glare. Light levels can be controlled in the usual manner with the headlight switch rheostat.
The gauge faces and dials, comprised of electrical conducting laminents, glow when alternating (AC) current is applied. AC current is converted from the 12V DC supply of the car by a transistor oscillator (Power Pack) mounted on the forward dash frame under the glovebox. This power pack supplies 250 volts AC at 250 cycles per second (250 Hertz) from the 12V DC car current.
All gauges are of the thermal type and operate on the 5V DC constant voltage principle. This is accomplished through the use of a voltage limiter connected in parallel with the gauges. Voltage limiters in all B Body MOPARS except thye 66/67 Charger are external plug in type. The 66/67 Charger Model uses a voltage limiter intergal with the Fuel Gauge.
Thermal gauges in MOPAR'S from about 1960 thru 1974 are of the electromechanical thermal type. A constant 5 volt DC signal is attached to one post, and a variable resistance signal from a sending unit is attached to the other post. A bimetallic strip is wrapped with insulated nichrome wire and will bend based on how much the wire heats up. Less resistance equals more heat and thus the strip bends more. One end of the bimetal strip has a tab which attaches in some fashion to the gauge pointer.
From the factory, the 5 volt DC signal is provided by a set of points inside one of the gauges, either the fuel (66/67 Charger) or the temp gauge (Some A bodies). Simple in operation, it is another bimetal strip with the same insulated nichrome wire setup. When you first start the car, the points stay closed for approx 2 seconds to start the oil pressure and fuel gauges moving towards their normal position. Since the input to the voltage limiter is 12V DC and the points are closed, the temp and fuel pointers move fairly quickly. After 2 seconds, the point open (0 volts DC) and then the points open and close rapidly to approximate 5V DC. This is 1950's technology and while it was the latest technology at the time, it has inherent problems. The primary reason for MOPAR thermal gauge failure is due to the points sticking intermittently closed for longer periods of time than designed. After 30, 40, 50 years of operation, the points start staying closed for a longer duration and instead of 5V DC, the oil pressure, temp, and fuel gauges get 7,8,9 or even 12V DC. This causes the bimetal strip to heat up past its design specs, and the insulation burns off the wire and if heated excessively for a long period of time, the wire breaks.
The following pictures illustrate a 66/67 Charger temp gauge and what the wire looks like after the points have started failing. It also shows the old burnt wire taken off and new correct wire rewarpped to restore the gauge function.
You can test whether the wire has burned in two by using an ohmmeter and testing between the posts. A reading of about 20 ohms shows the wire is intact, BUT without opening the gauge up, it is impossible to tell if the wire has been blacked by voltage limiter points failure. Once the wire has charred, calibration will be off even if the gauge still functions.
I have worked very closely with Premium Dash Decals to develop an overlay (read decal) that closely approximated the color and markings found on the original 66/67 Charger gauges. Over time, the original overlays faded with the sun and heat until they turned almost white. I'm sure you have seen faded instrument panels before on many of the old molars. I decide to offer the service of removing the old overlays, cleaning the old glue off of the gauge face, and reapplying the new overlays. I have done over 75 to date and I think they definitely make the instrument cluster look much better. The following are a few pictures of how a gauge face is replaced on a 66/67 Charger temp gauge.
Removing the instrument cluster from a 66/67 Charger is not all that problematic. Here are the steps I use when removing the cluster from my 66 Charger. I will also highlight the slight difference in the 67 due to the collapsible steering column introduced that year and tach wiring connections.
1. Disconnect the battery!
2. Remove the 4 screws holding the trim plate under the steering column. This will get you access to the nuts that are holding the the U-Bolt assembly (steering column support) in place.
3. Loosen one U-Bolt nut and remove one so that you can swing the steering column support bracket to the side and allow the steering column to rest on the drivers side seat. This will prevent the steering column from interfering with removing the dash cluster complete with bezel from the dash frame.
4. Pull off the radio knobs and volume/tuning wheels.
5. Use a deep drive socket to remove the two nuts holding the radio to the bezel.
6. Use a small allen wrench to remove the fan and temp knobs from the AC/Heater controls.
7. Remove the 7 Phillips head screws (including the ones under the AC/heater controls) that hold the cluster housing to the dash frame.
8. Carefully pull the top of the cluster assembly outward until you can disconnect the speedometer cable and then the two ammeter nuts (Red and Black wires).
9. Continue to pull the housing out so that you can disconnect the following leads:
Fuel gauge-12V power and half round connector
Turn signals, high beam and Lamps Not Locked lamp sockets
Yellow wire from tach positive terminal. NOTE: 67 tachs have both a double blue/white and grey wires
5V input and sending unit wires from temp and oil press
10. The cluster housing complete with bezel should now be able to be removed from the car.
FOR 67 ONLY:
Steering column can only be lowered by loosening the firewall bracket in addition to the above steps. This is due to the collapsible steering column on 67 models.
It is helpful to understand how the Chrysler gauges were calibrated in order to understand what the has marks mean, especially on the oil pressure and temperature gauges.
Oil Pressure Gauge:
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