Grounded Tach Wire Creates a Gremlin?

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I8NEMO

I8NEMO

FABO Gold Member
FABO Gold Member
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Location
Phoenix, AZ
1968 Barracuda 340
All Elec. Components new including harnesses. Charging indication at Ammeter Normal since day 1
60 Amp Alternator Square Back
2 Wire VR
No Stereo, No Electric fans.

When I reinstalled the steering column a couple weeks ago I lost fire to the motor. Tach wire was smashed in column mount. Repaired that, motor fired immediately. Now I have an overcharge above idle. Battery Negative to Motor Mount, then back to frame bolted into weld nut. VR also bolted into weld nuts. I've read much here, here are my testing values:

Key On Engine Off
Battery 11.95V
VR Blue 11.36V
VR Green 10.24V

600-700 RPM's Ammeter Gauge needle centered
Battery 12.V
Alternator 12.1V
VR Blue 11.7V
VR Green 10.58V

800+ RPM's Ammeter Gauge needle pegged on C
Battery 14.6V
Alternator 14.9V
VR Blue 14.2V
VR Green 7.6V
VR Flange to Negative Battery 21V, that's huge from what I've read.*

I noticed the overcharge after 2 short test drives totaling maybe 10 minutes of driving. During these tests yesterday and this morning I felt VR, wires, harness and inspected behind dash, nothing hot, no melting at this point.

*The VR flange to Negative Battery test at 800+ RPM's/Ammeter Pegged indicates a grounding issue somewhere correct or failed brush replace VR?
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What wiring harness did you use? That may be the wrong voltage regulator for the square back, think that’s for the round back. The mid 14 volts seems normal to me for charging. Mine runs there.


Should search “Madd Bypass” and dump the amp gauge for a volt gauge.
 
Do you have a big ground wire from you engine to the firewall? That gets left out in many engine swaps and cause all kinds of weird problems.
 
That VR you have is the OEM style, i think as scody mentioned, you need to change to the "triangle" plug style for 70 and up(I think)
 
For starters you have nearly .4V drop in to the VR. You said you measured battery at 11.95 (that is low) and VR at 11.36. That is not a lot but it adds up.

I don't understand your grounding description, is this trunk mount battery? That is cause for concern voltage drop

Check the VR GROUND Whether or not trunk mount, "rig" a wire (does not have to be large, no.18 is big enough)--- long enough to reach from battery neg post wherever it is, up to any part of the car. "Rig" the voltmeter to read from battery NEG post to the VR mounting flange. Run engine at fast idle "low to medium cruise" and check with loads off, and again with everything powered--lights, heater, whatever you have. You want a VERY low reading, lower the better, zero is perfect

Possible causes IN NO ORDER
1...Get a known GOOD and CHARGED battery in place for testing Battery can be sulfated. Rare for battery to cause problems but they can
2...Also rare on solid state VR is they can be off on voltage. But it can happen. Check voltage drop as mentioned first, both in the ground path and the blue wire "IGN" terminal of the VR all the way to the battery
3...Probably the largest single cause of over charge in Mopars is voltage drop to the VR both hot side and ground side

I don't see that your tach wire could have caused this, by the way
 
Looks like you have an alternator with one field wire, so you have the correct voltage regulator. Whether it is working properly or not is another question.
 
Mike69cuda said:
Looks like you have an alternator with one field wire, so you have the correct voltage regulator. Whether it is working properly or not is another question.
Click to expand...
I intended to mention, if you have an ACTUAL mechanical regulator it is suspect for voltage accuracy. Most all replacement regulators are solid state
 
Scody21 said:
What wiring harness did you use? That may be the wrong voltage regulator for the square back, think that’s for the round back. The mid 14 volts seems normal to me for charging. Mine runs there.


Should search “Madd Bypass” and dump the amp gauge for a volt gauge.
Click to expand...
Thanks, I'm considering the gauge change to voltmeter and the alternator to battery jumper. About the VR, that came specific from my friend/ guru who installed the Pertronix in the dist. So im not sure if there's anything different or special about it.
I don't get it, I researched this part of the build and went with super trouble free and it was perfect until this tach wire snafu. Harnesses came from Mr.Moparts, can't remember their source name but it was common. Maybe the tach wire short fritzed the gauge
 
67Dart273 said:
I intended to mention, if you have an ACTUAL mechanical regulator it is suspect for voltage accuracy. Most all replacement regulators are solid state
Click to expand...
Now that I think about it, I think it is solid state
 
4spdragtop said:
That VR you have is the OEM style, i think as scody mentioned, you need to change to the "triangle" plug style for 70 and up(I think)
Click to expand...
I gotta get with my buddy Bob who set up the dizzy with Pertronix, he handed me that VR and said wire everything factory. Hell now im questioning if Im 100% positive the gauge was in fact steady while running before the tach wire snafu. Im going with 99% lol. Or maybe 67%.
 
67Dart273 said:
For starters you have nearly .4V drop in to the VR. You said you measured battery at 11.95 (that is low) and VR at 11.36. That is not a lot but it adds up.

I don't understand your grounding description, is this trunk mount battery? That is cause for concern voltage drop

Check the VR GROUND Whether or not trunk mount, "rig" a wire (does not have to be large, no.18 is big enough)--- long enough to reach from battery neg post wherever it is, up to any part of the car. "Rig" the voltmeter to read from battery NEG post to the VR mounting flange. Run engine at fast idle "low to medium cruise" and check with loads off, and again with everything powered--lights, heater, whatever you have. You want a VERY low reading, lower the better, zero is perfect

Possible causes IN NO ORDER
1...Get a known GOOD and CHARGED battery in place for testing Battery can be sulfated. Rare for battery to cause problems but they can
2...Also rare on solid state VR is they can be off on voltage. But it can happen. Check voltage drop as mentioned first, both in the ground path and the blue wire "IGN" terminal of the VR all the way to the battery
3...Probably the largest single cause of over charge in Mopars is voltage drop to the VR both hot side and ground side

I don't see that your tach wire could have caused this, by the way
Click to expand...
The battery is in the factory position. I read an early post of yours and that's why I did the VR ground test from VR flange to battery negative the value is in my post: a whopping 21V
 
Somthing is wrong there, as there is almost way that can happen. The drop is generated by charging current and if it really were 21V it would likely be not charging at all or overcharging into very high values---boiling the battery and burning things up
 
67Dart273 said:
Somthing is wrong there, as there is almost way that can happen. The drop is generated by charging current and if it really were 21V it would likely be not charging at all or overcharging into very high values---boiling the battery and burning things up
Click to expand...
Got it, I'll run that again, maybe I made an error somewhere.
 
My observation...

  1. 21V is most likely a misread ov the , voltage meter. 2.1 or 0. 21 is most likely
  2. The old style VR and alternator are wired correctly.
  3. I admire your grounding, battery negative to engine block from block to dedicated welded post on frame.
  4. The OP shows very normal voltages, battery with key on is a bit low. Some of the voltage drops are more than I would like but not causing the symptoms
  5. OP states his ALTERNATOR guage is pegging on charge above idle.
    1. Causes for Alternator gauge pegging but voltage being normal
      1. Low battery
      2. High load
I ran my battery down till it would not start the car. I jumped it and drove around for 30+ minutes, the gauge was holding 1/2 way between center and full charge. Normally it will be there for a minute or so after the first start in a week.

I put the battery on a charger overnight and all was good in the world the next day.
 
Dana67Dart said:
My observation...

  1. 21V is most likely a misread ov the , voltage meter. 2.1 or 0. 21 is most likely
  2. The old style VR and alternator are wired correctly.
  3. I admire your grounding, battery negative to engine block from block to dedicated welded post on frame.
  4. The OP shows very normal voltages, battery with key on is a bit low. Some of the voltage drops are more than I would like but not causing the symptoms
  5. OP states his ALTERNATOR guage is pegging on charge above idle.
    1. Causes for Alternator gauge pegging but voltage being normal
      1. Low battery
      2. High load
I ran my battery down till it would not start the car. I jumped it and drove around for 30+ minutes, the gauge was holding 1/2 way between center and full charge. Normally it will be there for a minute or so after the first start in a week.

I put the battery on a charger overnight and all was good in the world the next day.
Click to expand...

Switching batteries was going to be my next move. I read a lot before wiring this car, it's what prompted the new harnesses and sturdy grounds, it's easy to overreact fearing a mistake causing a melt down but with all the great input here im beginning to think the issue is simpler as you've described. Just like any other issue I have to keep after it. Thanks
 
I8NEMO said:
1968 Barracuda 340
All Elec. Components new including harnesses. Charging indication at Ammeter Normal since day 1

Key On Engine Off
Battery 11.95V
VR Blue 11.36V
VR Green 10.24V

600-700 RPM's Ammeter Gauge needle centered
Battery 12.V
Alternator 12.1V
VR Blue 11.7V
VR Green 10.58V

800+ RPM's Ammeter Gauge needle pegged on C
Battery 14.6V
Alternator 14.9V
VR Blue 14.2V
VR Green 7.6V
VR Flange to Negative Battery 21V, that's huge from what I've read.*
Click to expand...

Looking at your readings, I'd guess a defective alternator. First case, engine off, sense voltage (blue) is right at battery voltage and field (green) is nearly at battery voltage. This makes sense. Second case, engine below 800 rpm, field voltage at 10.58 volts and no indication of charging? With that much field excitation the alternator should be charging at a high rate. The third case, the regulator is decreasing the field voltage to less than the second case (7.6 volts) but now it's charging at a high rate as evidenced by the rise in battery, alternator, and sense voltages all being over 14 volts. Just my thoughts. Edit: Is it possible that you have a poor ground between the alternator and the battery? I know that's a long way from the steering column but....
 
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Finally got back to this "issue", charged the battery overnight 2 days ago, this morning had 12.8v at the battery, ran engine and all is well, Ammeter behaving in normal range. I wear many hats as a business owner, one of them is "risk management" aka Michael Clayton and I think over the years I've become predisposed to see problems bigger than they are. I'm glad this was simple and sure appreciate everyone chiming in here.
 
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