Ford Instrument Cluster Voltage Regulator Assembly

Solid State Retrofit

TRIM - Dashboard Section

The original Instrument Cluster Voltage Regulator has been called by many names including, Constant Voltage Regulator (CVR), or Instrument Voltage Regulator (IVR).  Ford's gauges started as 6 volt, wired straight off the Ignition Key Switch.  The last year for six-volt systems was in 1955.  In 1956, Ford went to 12-volts.  '56 was the only year the instrument gauges and sending units were 12-volts and again, no CVR.  In '57, Ford quickly went back to using six volts for all the gauges, corporate wide, and mechanical CVRs remained until at least 1988.

The OEM CVR works much the same as a turn signal flasher with three leads: One goes to Ignition power, one lead to ground, and the other to the gauges.  So the original pulled 12-volts through a resistance wire that was wrapped around a bi-metal strip, to ground.  As the bi-metal strip got hot, the normally closed contact would open, then cool and close, over and over as long as the key was turned on.

The OEM assembly comes with an adjustment screw (that is painted), but none of the manuals explain how to adjust the timing.  A 6-volt average of 12-volts would be an on and off time of 50%, or 50% duty cycle.  I put my Fluke meter on one and checked for Hz.  It was all over the map, from 0.4-seconds to 1.4" and very erratic.  I realize this was a cheap way to get 6-volts back in the day.  Now we have much better methods.

For the scope of this site I retrofit a 6-volt Solid State regulator into the original metal case, showing each step.  Then I test it.  As a 'base', here is the Master Parts Catalog numbers for Ford CVRs (with mounting fastener info):

This is the location for Squarebird CVRs.

These are two broken units were removed from different Squarebirds.

The first job is to open the case.

I'm working on opening the third side.

That's it.  Let's see the inside...

The bi-metal strip on the right side is wrapped with very small resistance wire which causes it to heat.  This one is burned open.  Notice the end of the tiny wire goes under an edge clip for the ground connection.

Notice the grounding clip (in the foreground) is corroded on the inside.  This is a recipe for disaster because six volts doesn't need much to insulate it from ground.  Also notice the 'adjustment' jack screw in the background.

One last look before I tear into it.

The original connectors are good and tight in their rivets.  Notice I left a stub of metal after taking the arms off.  I tin these and solder 12-v 'Input' and 6-v 'Output' wires to them.

I removed the adjustment screw.  This is a perfect hole to put a green LED to show the 6-v side is on.

All holes I drill will be 1/8".

The solder I use (AQUABOND by KESTER) contains NO lead and is Silver Bearing.  Yeah, it's the good stuff but you get what you pay for.

Projection welds hold the bottom strap to the case, leaving dimples in the sheet metal surface.  I am creating a flat, smooth 'bed' for the regulator. 

Time to talk about the Electronics...

This is a Fixed Output, LM7806 Voltage Regulator in a TO-220 case.  The center leg (2) is also electrically connected to the metal backing with the mounting hole.  So conveniently, the case will be our heatsink and our ground.
All I need is two capacitors (C
1 = 0.47uF) and a very small LED with a dropping resistor (270-ohms).  I am using the correct 0.1uF for C0, but a larger cap for C1 because car electrical systems are notorious for voltage spikes and drops.

To prevent metal fatigue, it's important to hold the leads with pliers, away from the case, while bending the leads.
These regulators come from the factory with internal short-circuit and overload protection.

Place the TO-220 in the housing and mark the 1/8" hole.

These are the setup parts: A 1/8" pop rivet, a 1/8" hole brass washer, and heatsink compound.  Now I am ready to wire.


Solder three short leads onto the regulator.  It's hard to see but I marked the power leads, red (12-v) and black(6-v).

Use plenty of heatsink grease and pop rivet the parts together.  Set it aside for later.

I used epoxy to mount the LED.  After it cured I added a dropping resistor (270-ohms@1/8-watt), insulated the 6-volt leg and soldered it to the output post.  Notice the NEG leg is sticking up.

I added the 0.1
Uf capacitor to the same output tab.  Now I have two NEG legs sticking up.

The (0.47uF@50v) Input cap neatly nestles in the middle.  Now, all three NEG legs stick up together.

Time to solder all the NEG leads together, then solder the power leads to their tabs.  The next one I assemble will have shorter wires, but notice that half of the 'can' is empty.  That is the portion where the bulky parts fit into.


I used a wide chisel to hem the edges.


Here it is... On the left, 12.56-volts from a car battery (IN).  On the right, a solid 6.00-volts (OUT).

The indicating LED looks like it belongs there.

If you want a totally bone stock look, I can conveniently leave the green LED out.

I want to extend a special "THANKS" to Yellowrose (Ray Clark) and NYsquarebird58 (Marcelo Laviano) for sending me their old CVR units. Without them, I was stuck with the electronics in a breadboard, but no real way to test it.  Now, we can save our members at least US$25 over retail price.  I offer a free 'no questions asked' warranty on all my CVRs.  Simply send the bad unit to me and I will repair or replace and return, a tested-good solid state unit to you, period.  I don't need paperwork because I can easily identify my work and materials.

JohnG also contributed tremendously by scoring twelve old units from a bone yard as cores.  That helps quite a bit because not all old units can be opened successfully.  Thanks, John.  - simplyconnected

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