Before I changed my external voltage regulator the voltage was reading 13.8-15.1 running at idle and would rise as I drove. Now with the new regulator the voltage reads 17.4 at idle and after driving less than a 1/8 a mile something behind the cluster starts smoking what could be wrong?

Faulty regulator, poor regulator ground, or high resistance in wiring to regulator and/or from regulator to alternator.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

How do I ground the regulator? And would a bad instrument voltage regulator mess up the voltage

Run a wire from the alternator housing (look for a small empty round hole on the back of the alternator, which may or may not have the letters "GRD" near it) to the base of the regulator. Secure the wire at the alternator end with a short self-tapping screw, and under one of the regulator mounting bolts. Run another wire from the regulator base to the battery negative terminal.
No.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Quick question, what kind of volt meter did you use? Reason I'm asking is my truck's gauge pegged out at what I would guesstimate to be about 30+ volts when the regulator went south. With a digital voltmeter, it was more like 17. still enough to fry some dash lights, but they probably needed replacing anyway. I don't have much faith in factory gauges.

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If it was easy, everybody would be doing it.

Guessing that its stock. And I'll try the grounding process after I reinstall the valve body on the 904

Don't think the grounding process worked although I ran a wire from the base and one of the bolts. Could the alternater wires be on backward?

Gage in dash measures current, amps flowing, and in what direction; flow from battery indicating a discharge or in other words alternator not keeping up, and charge ,current flowing from alternator exceeding battery's contribution.

Think of voltage as pressure, or a force which moves electrons through circuit.

Voltage drop which is a result of increased resistance be it from corrosion at connectors, within various conductors, or devices such as switches. Every volt dropped along ground path, and circuit between battery plus terminal gives voltage regulator false information, and regulator signals alternator to increase output to over come whatever the voltage drop is to bring harness voltage up to 13.8 to 14.2 v. Example if harness voltage is 12.8 v at blue wire plugged into voltage regulator, alternator will bring up output to 13.8 + 1 volt or 14.8 volts. This may be some of your problem.

Additionally faulty components can contribute to charging problems. If battery can't receive and hold a charge because of a bad cell, or it has been drained dead one too many times, whatever, charge voltage will be high. If voltage regulator is faulty it will cause an over charge, or some times an under charge. And lastly various alternator problems can cause excessive charge, or no output. Any new component can be defective out of the box, so don't discount it as A-OK, test everything.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

No. Sounds like high resistance in the ignition switch and/or the wiring to the ignition switch and/or from the ignition switch to the regulator and/or from the regulator to the alternator.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

what could be the high resistance. I have added a couple new wires. tach, msd 6a box that wires to a points type distributor, electric choke and a new regulator. because my old one wouldn't stay hooked up.

Um…I just listed the possible point(s) of high resistance for you. You're going to have to do some step-by-step diagnosis, or get the car to someone who can.
Then it's also entirely possible some of these new additions were improperly hooked up, in a manner that pulls extra current through the circuit that's supposed to feed the voltage regulator, dropping the voltage the regulator sees and causing your problem.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I think I know exactly what it is. I didn't hook the tach straight to the battery. its on something near the location of the ballast resister. never thought about it after hooking it up to see its operation.

Tachometer won't draw much current.

You have to check for voltage drop at each connector and switch as well as ground path between voltage regulator and battery. One crusty negative battery terminal connection by its self can cause a 1 volt drop or more.

Keep in mind every point there is a little voltage drop all add up to one big drop. Example: 0.5v at battery negative terminal, 0.25v at bulkhead connector in and 0.25v back out, and 0.1 v at switch, and 0.1 volt on ground side of voltage regulator all would add up to 1.2 volts causing regulator to elevate normal harness voltage from 13.8v to 15 volts.

Be sure you have a good ground path between head and fire wall by installing a ground strap connecting the two. Clean all ground connections, use star type lock washers on back side of voltage regulator backing plate and mounting bolt to help bite through any paint & rust for a better path to ground. A additional ground loop connecting voltage regulator, spark controller if equipped, alternator's case, and back to negative battery terminal will grantee no voltage drop on ground side of ignition circuit.

If you have an electric choke, use a relay to power it from battery or stud at starter relay, and use the blue wire on 12v side at ballast resister for the trigger circuit. This will give back about 1 volt of drop.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

So I grounded the regulator from the other side of the base to the battery and ran the tachometer the the battery. Not high anymore but seems like it's to low 12.4-15.3 in park and 10.3 at idle with lights on. I also have a aftermarket radio equalizer and 12v plug in. All powered by the stock radio source.

15.3 is high, 12.4 is low, 10.3 is way too low. Are you sure your battery is healthy? Sounds like it might have a dead cell. To check, with the engine off turn the headlamps on for two minutes. Then turn them off and measure the voltage right across the battery.
This is a fire waiting to happen. The original radio was about a 10-watt device.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.