Help with Volt Gauge flicker.

Lil Scamp said
We just installed an aftermarket instrument cluster and gauges on my dad's 71 duster. I advised him to also re-route the alternator wire bypassing the bulkhead connector as he now has a volt gauge instead of the amp gauge so we did. The car has always had a bad light flicker and you can really notice it now with the new volt gauge bouncing from 14v-16v. After lots of searching I see its not uncommon when a MSD 6AL is installed (which has been on there since the car was built). I found a thread on another forum which was successful after a diode was installed from the ignition wire from the MSD box. I tore apart an old radio and found a diode and spliced it inline with the wire, no change. The weird thing is, if you take the ignition wire feeding the voltage regulator off and hook it directly to the battery, the flickering stops and it charges perfect. Has anybody had this problem and had success fixing it?

Here is the successful thread: Ammeter/Main Voltage Fluctuating | Moparts Question and Answer | Moparts Forums

I am new to the forum but wanted to share my experience related to the OP's original post ... I have an '67 Barracuda that I converted from a slant 6 to 360 crate motor. I originally installed a chrysler orange box ignition kit and electronic voltage regulator with a stock replacement 3 wire alternator and wired into the original harness with a ballast resistor. I used it for almost 8 yrs with no charging problems with the ammeter bypassed and a new voltage gage wired into the harness. This spring I decided to start taking the car to the track and wanted to put an MSD iginition on to give me some versatility and rev control. Removed the orange box and ballast and wired up the new MSD Digital 6. Voltage gage now bounced around and lights flickered at a steady rate not related to engine rpm. I pulled my hair out for hours ... changed the MSD power wiring, went thru all my grounds, checked voltage drop thru the harness, new VR, new alternator ... everything I could think of and nothing changed it. Thanks to this thread and Lil Scamp's note about how it went away connecting the VR right to the battery, I decided to wire my VR right to the starter solenoid battery post ... And, viola, the problem went away.

I am fairly proficient at electrical wiring and have wired lots of stuff but this one has me stumped. I would love to hear some theories on why this happens ... my best guess is the MSD causing some kind of feedback or surging thru the harness itself and thus the VR senses this surging and acts appropriately. What's puzzling is the harness is fed off the same starter solenoid post that is now feeding the VR.

In any case, hope this post can help the next person that has this problem and save them hours and money!