70 roadrunner with 70 amp alt. constant output voltage regulator 3690731. been having miss in motor which turned out to be connection at ballast resistor. While trying to track down problem measured voltage going to ballast and it was jumping between 16 volts and 18 volts when car is running. 11.5 when not. Question is, this means Regulator is bad?

Sounds like a bad regulator ground based on the higher than desired voltage and the erratic behavior.

I am running a pertronix III with the multi spark would that make voltage at coil diffrent? I just tested my friends Chevy with MSD and its reading 25 volts at + side of coil.

I have a 70 rr also, 95amp. alt. mine was running 15-15 1/2 volts put this voltage reg. on and now I'm at 13.8-14.2.don't waste your time with local parts store ones I couldn't find one that worked.This is the one I used.
Mopar Voltage Regulator ( P4529794 )3438150 from summit.

I would think running at 20 volts it would burn everthing up.

It will if it hasn't started already.I wouldn't drive the car until you get the voltage down.
Maybe others will chime in.

The 731 is as you noted the race reg. get a regular parts house electronic reg & see if your voltage comes back down to an acceptable level. I would not run it until you do

So confused put a stock regulator on with a good external ground same thing now hovering around 20 volts but every so often 13.5 will flash on meter. Just think something else is going on.

Yes definitely something else going on. possibilities are that the green wire from alt to reg is intermittently touching metal/grounding out & making it full field for a split second and related thing with the alt brushes/field circuit (them grounding out & full fielding it. got another alt you could toss in for a quick test? for the "green wire" possibility, a good visual along its length or pull the triangle connector from the flat reg & pull the green wire off of the alt & with a jumper connect alt to reg (side terminal) and jump 12V (blue ign1 circuit) to the reg top terminal. the recessed reg nubs are a slight pain to jump. EDIT I'm wondering if it might be the digital meter? if you have a 12V bulb such as a 1157 lit up nearby does it change brightness when the meter changes reading?

thanks for the info will try tomorrow. I think its time to walk away for now. Been working since 6am and I'm spent/frustrated.If anyone has ahigh output alt with a pertronix III conversion please take a reading with digital volt meter at + coil while running and let me know what your reading. Thanks for the help

try reading this
http://www.highimpactperformance.org/files/mopar001_1_.pdf

Robert hope your still out there. Couldn't leave it alone. Did the green wire bypass 14.2 volts. KOOl so hook everthing back up normal its all working 14.2 volts now I'm really confused. I then relize to easy checking stuff I jump ground DVM to the body. If I ground meter to engine I get 20 volts if I ground it to the body I get 14.2???? I have ground strap from motor to frame. Battery is in trunk grounded to frame. Any thoughts from anybody?

Voltage regulator is grounded to the body, alternator is grounded tot he engine. The problem you are seeing is the ground between the body and the engine is bad.

Run a quicky jumper from the alternator case and voltage regulator and see if everything is as it should be.

As I suspected, with the two voltage readings, a poor regulator ground. Just not at the firewall. I agree with Supercuda, run a temporary ground between the body and engine and see what you get. One lead of a pair of jumper cables works great for this.

Ran jumper wire from alt case to body no change. Used jumper cables from bumper bracket bolts to motor mount bolts and power steering pump DMV jumping all over the place. My ground cable runs from intake manifold bolt to sway bar bracket bolt on k member. Being manifold and heads are aluminum could this cause grounding problem?

Why are you reinventing the wheel.

Your ground choices are not good ones.

Run the jumper from the ALTERNATOR to the REGULATOR directly.

Anything else is just wasting time.

Okay will do thanks. will post outcome.

After your last post I am not so sure I'm right. Try two things. First with the engine running take a voltage reading between the alternator case and the body. This will check how good the ground is. Second with the engine running take a voltage reading between the output stud of the alternator and the battery post on the starter relay (I'm assuming that's where you terminated your remote battery lead). This will check for voltage drop on the positive side. Problem may be on the positive side and not the negative (ground) side.

Will do . What kind of readings am I looking for between Alt case and body?

Both cases are similar. If you have a good ground between the case and body you should read close to 0 volts. If you have anything else, what you are measuring is the voltage drop through a poor ground connection(s). If you have a good connection between the alternator output stud and the starter relay stud, you should again read close to 0 volts. If you have anything else, what you are measuring is the voltage drop through a poor connection(s) on the positive side. You have to keep in mind that the system voltage the regulator is using for a 'sense' voltage is coming from the stud on the starter relay through the ignition switch.