i just read a couple of articles on how a CD ingition works. it's entirely possible that the small red wire is pulling voltage in on/off cycles. what happens is the power charges a capacitor in the MSD. when that capacitor is 'full' it no longer needs voltage. as you rev the car, the cycles happen so fast that the guage can no longer keep up (visually)and the gauge looks to steady out. without seeing a wiring diagram of the insides of the unit i can't say for sure. i'm also not clear why the box requires 2 input voltages (heavy and small red wires).

Have you checked the wire connections on back of your alternator guage on the cluster? They are known to lossen and give offset readings. I have fixed many with this issue in years past. Not saying that is your problem but doesn't hurt to check.

I will check the back of the ammeter for a loose connection and I will disconnect the volt meter that is connected to the 12v MSD feed.
Thank you.

I took the attached picture back when I was running a ballast and the Mopar orange box. When I removed the ballast and added a 12v coil, I took all seven wires and connected them together and the car ran fne. Then when I swapped to the MSD box here a few weeks ago, I only used two wires, "single" brown (crank-not shown in picture) and blue (run) and the car starts and runs.
In the picture:
Light Brown: Crank/Ballast/Coil splice
Light Brown: Ballast to + coil
Green [Red tracer]: Un-used
Light Blue [Yellow tracer]: ECU to Run
Black [Yellow tracer]: ECU to - coil
Black: UNKNOWN
Blue: RUN
Not Shown: Light brown main feed for CRANK.

It appears that all three light brown wires are spliced from the same CRANK wire. I believe that I only need one which I currently have.
The blue RUN wire is required and currently wired.
The Green/RED, Light Blue/Yellow, Black/Yellow were coming off of the Mopar ECU and are no longer required.
The last wire that I do not have accounted for is the second Black wire shown in the picture.


EDIT:
The ammeter connections were tight and I changed the connection for the MSD volt gauge so that I can disconnect it and then reconnect it for a test.
I am going to wire in the blue run wire, the brown crank wire, and the double brown wires to the MSD 12v switched wire and the recheck the ammeter reading.
EDIT:
* I just found the connector for the 12v Blue-RUN/Brown-Crank to be "wiggle" loose. This feeds the 12v source for the MSD box. I "crimped" the male/female connector this time and there is no movement. Hopefully this may have been the issue. I will try and start the car this weekend to see what the ammeter is doing now. I will leave the 12v gauge disconnected at first then add it back in to see if there is a difference at the ammeter.
I also ran an external ground wire from the alt body to the battery negative ground wire just in case.

Thanks

as much as a PITA it is, try and only make 1 change at a time!

""try and only make 1 change at a time""
I usually try too but this time I have backed myself into a corner. We have 45 degree weather outside right now and in two days it will be in the 20's. So I am doing a few things together to try and find the issue.
thanks for the reply.

I hope that this loose connection was the issue since the alternator, ammeter connections, and two VR's checked out. I am still a little worried that one loose connector could make the ammeter jump this much. It was the BLUE-RUN wire connector though.
Thanks Robert.

I charged the battery to about 80% and then started up the car without the volt gauge hooked up to the MSD 12v source wire.
At 1200rpms high idle, the battery voltage guage and the ammeter still fluctuated but not as bad. The voltage guage showed 14-15 and the ammeter moved from straight up to about 1/4" to the + side. It never showed discharge.
At 950rpms, the voltage guage showed about the same and the ammeter moved from straight up to about 3/8" to the right. So it shows worse still at a lower rpm.
The interior dash lights were changing brightness up and down too during the idle time but not at high idle.

What if the issue is something inside of the car and not in the engine compartment? Could a loose connection anywhere in the car cause the ammeter to fluctuate on the + side? If so, since the dash lights are fluctuating, should I track down that circuit to look for an issue?

Thanks again.

since none of this was happening before the MSD upgrade (right?) i would examine every circuit on every wire that you had to touch/change for the upgrade. i could very well be tied only to the interior lighting since the lights for your extra guages are probably tied to that curcuit. did you install the guages or were they there when you got the car?

Mike,
I do think that the dash lights were pulsating before the MSD swap but I do not recall if I noticed the ammeter/volt gauge fluctuating at that time. I added the dash light issue onto my Winter list a while back but I did not think about it being the issue of the ammeter until now. I have checked and rechecked the wiring for the MSD and I do believe that the MSD install is now good. When I saw the dash lights fluctuating today, that got me to thinking about the issue just before I parked the car for the Winter.
The guages are mine and I can trace the dash wiring fairly easily.

MSD Note:
I can already see the difference in how much easier the car starts with the MSD installed. The engine has started right up each time I have started the car even in the cooler outside temps. It will even startup without touching the accel pedal. I never had that with the orange box or the two FBO boxes.
Thanks for your reply.

i didn't think the 2 (MSD and jumpy guages) were ever related. just the keyed power source. i'm glad you like the MSD, you'll see a bit of a jump in throttle response off a light and better gas mileage. what kind of car are we talking about here, i've totally forgotten

It is my Challenger in my sig. I plan on chasing the instrument wiring to see what I can find and also checking the bulkhead connector just to make sure.

Thanks again.

This is a long shot, but one time when I had my car serviced they returned it and the gauges were pulsing at a constant interval and I could also hear a little bit of noise behind the dashboard. I took it back the shop and they said it was probably a bad voltage regulator. I swapped out the VR and same problem. I was scratching my head because I could not figure it out. In desperation I started messing around with all the dials on the dash and it turned out to be the wiper delay switch was on or engaged in some funky mode where all the gauges were pulsing but the wipers were not moving. Once I turned the switch to off it quit doing it. This is most likely not your issue but I figured I would throw this out there if it was something you wanted to check. Hope you get it figured out. Keep us posted on what you find out.

Loco,
Last night at 2am I read your response, I ran out to the garage and went directly to the wiper switch on the car. Crapt! That was not it! I was very hopefull though. Under the dash I go.
Thanks allot for your reply.

One thing that I thought of this morning was that when the key is in the RUN position but the engine is off, the battery volt gauge is steady. But when the car is running is when the gauges start fluctuating. I assume that this is due to the alt not charging and it means nothing.

I may have found one issue under the dash. I found a wire going into the headlamp switch with melted insulation. It is the pink wire. After I fixed the end, I turned on the headlights (all the way up) and I had lights but no parking lights. Then I tried the parking lights (mid position) only and I could not get the parking lights to light up until I pushed in on the switch and then they would flicker. It appears that I have an internal issue with my headlamp switch.
I know that they are not made new, so what are my options?

Thanks

i don't know what an E-body headlight switch looks like but i have pulled apart switches on my road runner before and clean them up. there is also a member who rebuilds them over in the 'hot new products' area. here's a link - https://board.moparts.org/ubbthreads/show...e=2&fpart=1

Mike,
Thanks for the link. I have already pm'd him to see what options I have.

Thanks a bunch.

My headlight switch ended up being good but my 12v feed wire to the switch was bad. It is fixed now.

Could a faulty battery cause the ammeter/battery voltage to fluctuate (13v-15v) if the rest of the electrical system is good?
Note: When I attach the (+) battery cable to the battery, I get a spark.

Thanks

""Something is still on that shouldn't be, . Stay with it ""

CRAPT! Thanks Robert.

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""Could a faulty battery cause the ammeter/battery voltage to fluctuate (13v-15v) if the rest of the electrical system is good?""

I am going to have my battery checked tomorrow just to make sure.

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I should have my new alternator from Powermaster this week and I have a new voltage regulator to test too.