Mopar Instrument Cluster Voltage Regulator Upgrade Build

Required Parts:

• A small silicon chip to replace the regulator.
  Find any shop that sells chips, and tell them you want a “7805” That's it. Don't worry about the specs, a 7805 is a 7805, pure and simple. (See photo 1.)
• A small heatsink with a hole, so you can slip a bolt first through the 7805,then the heatsink itself. Any small heatsink, don’t get carried away. (See photo 5, it is the black, vented piece beneath the chip.)
• Heatsink compound, in a tube. It is white.
• A spool of 20 gauge wire, solid or stranded. I used three spools, only to have three different colors. But one is fine, if you are careful.
• A small electrolytic capacitor. It must be between 5 and 100 uF, with a voltage rating of at least 15 volts, or more. (See photo 2.)
• Heat shrink tubing, if you like. It’s so easy to use, why not?
• A soldering iron/gun setup, low powered, as these parts and wires are delicate. I used a Weller 100 watt gun.

The heatsink, heatsink compound and wires were obtained at Radio Shack. They have a nice three-pack of the wires, in three colors. I went to numerous Radio Shack stores. They all had these parts in stock, but none of the other parts. Surprisingly, the salesmen all knew nothing about chips or capacitors. The chip and capacitor were finally located at a local electronics specialty shop. The salesman there explained how a 7805 was the same regardless of manufacturer. The numerals say it all to these guys. I spent about $20.00 in parts, not counting the soldering supplies.

Now, the 7805 takes whatever voltage the harness throws at it, and sends exactly five volts the gauges. It gets warm, so the heatsink keeps it cool. The capacitor is only there to absorb voltage spikes, to help protect the 7805.

Photo 1	Photo 2
Photo 3	Photo 3a

Photo 4

Photo 5

Procedure

Please refer to photos 3, 3a, and 4, throughout.

You are looking at the back of a 1964 Fury dash. In photo four, you can see a close-up of the three prongs where the old regulator was unplugged. Ground is on your left. 12 volt power from the harness enters through the center plug. Power goes to the gauges at the right plug — this is where you want five, steady volts. Now, the capacitor will either have a “+” sign or a “-” sign, with an arrow pointing out which is which. If all else fails, look where the wires enter it, on each end. The wire entering a solid, metal end is always the ground. The other end looks kind of like plastic. When you have one of these in your hand, you will easily understand. Solder the negative side to the left, ground prong on the dash, and the positive side to the center, 12 volt-in prong. That's it for the capacitor.

Now, find a place to mount the 7805 and heatsink. In photos 3, 3a, and 5, I removed a pedestal bracket that held the harness, and used its bolt to mount my new components. Two areas of concern: There is an alignment ridge on this mounting surface, and it MUST be ground down. The heatsink MUST sit flush. Second, I had to carefully drill out the holes in the 7805 and heatsink to accept the bolt. Do this and test fit BEFORE soldering! Once satisfied, carefully bend out the outer two prongs on the 7805, cut three wires 5 or 6 inches long each, solder one wire to each prong, and heatshrink wrap. In my example, left to right on the chip, I used red for the 12 volt in, black for ground, and green for 5 volt out. Once everything has cooled, apply a thin layer of heatsink compound between the 7805 and the heatsink, and on the back of the heatsink, where it touches the metal dash mounting pad. This is the milky substance you see around the chip in photo 5--it oozed out a bit. Then, carefully and securely, bolt these items in.

Now carefully bend the wires to where they will be soldered to the three circuit board prongs. I made sure to route them around the dash light sockets, so they can be accessed if a bulb ever burns out. (See photos 3 and 3a.)

Now solder the three wires to the prongs in the dash. First, the center on the 7805, which is ground, to the left prong on the dash, which is also ground (black wire). Next, solder the left on the 7805 to the center prong on the dash (red wire). With this wire, 12 volt power from the harness entering the dash is routed to the INPUT side of the 7805. Finally, solder the right on the 7805 to the right prong on the dash (green wire). Thus, 12 volt power entering into the dash flows up the red wire into the 7805, which knocks it down to 5 volts, which then is sent via the green wire back to the dash, powering the gauges.

All is well in a steady gauge world!

I'll report the results as soon as I get the instrument cluster installed in my 1964 Plymouth Fury. My Fury will not run again until Spring 2006, so I report then how my instrument panel voltage regulator upgrade works.

Update 2008

I got my Fury running, but the engine went bad right away, and I still have not finished it. However, I dropped the instrument panel in my parking lot and split the circuit board (Doh!). I quickly replaced the whole unit with a regular one, just to get going. I have yet to modify one again as per the above article.

However, since this article was posted I received a couple nice e-mails to thank me for writing this article: they informed me that they followed the directions completely, with great results. So, thanks to the 1962 to 1965 Mopar Web Site posting it, we now know the modification works well!

Thanks Sean!  

Gary H.