I am collecting the things I need to upgrade the electrical system on my '77 Aspen Wagon, and during my search I came across some interesting reading, among other things about ammeter shunts. This is a subject I have seen being discussed in depth earlier here in the forum, but perhaps without a simple illustrated explanation.
I was looking for a fuse block, and I started by finding a very nice one, I think it has been shown earlier in this forum's pages, from blueseas.com, a company that makes high quality marine products. If it can tackle the harsh marine environment, it should be suitable to have under the hood of a car. The winter slush in the streets here in Oslo is salter than the Red Sea! I browsed their pages, and was impressed by the seemingly high quality products served in a very good website, and found lots of interesting reading about subjects equally suitable for cars in their resources section, under Reference and Technical Briefs. Her are some examples that may be helpful or give some insight:

Sizing a Shunt to a DC Ammeter

Strategies for Monitoring DC Current

Voltage Drop in Conductor - Wire Sizing Chart

Allowable Amperage in Conductors - Wire Sizing Chart

Part 1: Choosing the Correct Wire Size for a DC Circuit

Part 2: Select a Fuse and Fuse Holder For Your DC Product Installation

There is lots more to click on there.


Update Sep 18, 2010:

I have made extensive searches for sources for wire and fuse sizing, but have not found any that I think are better than the ones above. I have, however, found some fascinating websites, many of them related to boats, since the use of electricity at sea always has brought about some interesting solutions to serious problems, some of them very related to our cars. Among them is the british SmartGauge Electronics, an engineering company formerly run by C. W. "Gibbo" Gibson, who spend most of his life on a boat, and is the designer and manufacturer of some very specialised, high quality products. His insight into batteries and charging seem to be a rare combination of theoretical depth (ever heard of Peukert's Law?) and practical knowledge from everyday life on a boat. A great deal of his and his coworker's knowledge is presented in the Technical Info, and I recommend that you take some time to scroll down and follow the many internal links for some very interesting reading. I can garantee there are issues there that most of you didn't have a clue about beforehand!

For those of you using the metric system - or is not afraid to do some conversions between wire size in gauge and square mm's, he also has an interesting formula for calculating metric wire size.

The drag racers among you that would like to have a switch to turn off the alternator to reduce parasitic losses when flying down the strip, could take a look here.

To use his own words:
Website best viewed on a computer of some sort.

Update Sep 20, 2010

Remember to double the wire lengths when calculating sizes in the tables linked above; current travels from the source through the destination and back again in the ground wire.

Olaf

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Aspenized

I have a bit of encouragement to offer here. I have said this before, but for those who are new, or don't remember, there can be enormous voltage loss through the bulkhead connectors and the ammeter, that can seriously effect the efficiency of your ignition. But this loss seems to effect the electronic ignition especially. When I switched over to electronic ignition back in 94, this car with all stock everything dropped from 16 MPG on average to 13 MPG. Odd but true. I was pretty shocked. I replaced the coil, and tuned it up, and still just 13 MPG. I installed an MSD and still no cigar. Maybe 14- 15 once in awhile.

Then I measured huge voltage drops from the alternator to the ballast resistor. When I replaced all the wiring in the ignition system,and bi- passed the ammeter, the mileage went up to 18MPG on average. Before I was finished with the stock set up, I was close to 20 MPG with an old tired engine, which seemed to be a reasonable accomplishment. When I switched to the super six 2 bbl, the mileage rose to 22 from time to time. When I installed the OD tranny, I got highway mileage of 25 once in awhile.

The biggest improvement, however came from the very stuff Olofla is talking about here in this thread.

It is well worth fooling with. The old Mopar electrical design is a bad idea that gets worse with age.

Sam

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Sam, here are two pics that confirm your experience. I took the measurements from my '77 Aspen when installing the HEI ignition, pics are taken without motor running.

Reading taken from battery.
Reading taken from ballast resistor.

I know that some of you disagree, but I personally think running all current through an unshunted - and in earlier models unfused - ammeter circuit is madness. Knowing that wires, solder points and insulation ages rather badly, especially those under hood or in open air, doesn't exactly improve the situation, and makes for one thing to check regularly and modify before a fire results.
Mopar cars made after 1976 had an ammeter shunt, trucks after 1983/84.
As I told in another thread recently, my car stopped a week ago, and I had to spend some hours roadside to find and fix it. The reason was that I wiggled the 'fusible links' when physically checking my wires and connections when installing the HEI, just to be on the safe side (!) and then - without knowing it - almost broke off the solder in the end of two fusible links. Heat and vibration took care of completing the job. Winter project is changing ALL wires and connections that are exposed to the elements, and replacing fusible links with time-delay fuses. The stuff I link to above, is made by Blue Sea Systems, and is marine quality that is made to meet the Coast Guard requirements. It may be overkill, but I also intend to use marine tinned wires and fuses on all under-hood or open-air circuits to eliminate future problems (with those prices it may be just one wire a year!) .
Just this evening I registered strange and unknown noices from my alternator, and the headlights visibly changing their light output even with steady rpm's as I came up the street where I live. Good thing I just ordered a new alternator!

Olaf.

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Aspenized

Thanks for the photos. That was great visual evidence. I was losing a full volt and a half on my Dart. That is over 10%. And it seems when the solid state electronics are not getting full voltage, they just do not seem to work very well. The old points system did not seem to mind the voltage drop.

This need was further heightened when I switched to EFI. The electronics in that became even fussier about having the voltage steady. There is an internal voltage regulator in most EFI systems, but there is a limit to what they can accomplish.

I remember looking at the Blueseas stuff back when I did this, but was too far into the project by the time I was aware of their existence. Now I kind of wish I had gone back and started over. My stuff works, but it is basically the very modest parts you can pick up from Advance Auto, or Pep Boys. It is clunky and awkward looking, and not protected with covers of any kind. I am working on some way to get it all covered so I don't melt a screwdriver or wrench some day when they accidentally touch the Batt terminals that are currently exposed at various places under the hood.

Sam

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Great post Olafla,this should be a sticky,as it will help lot's of people.I changed the splice point on my Volare' for the ampmeter shunts.I connected it over a wider section of wire to make the ampmeter more sensitive.

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V8?? We don't need no stink'n V8!!

Can somebody link me to a good, simple explanation of how to cut out the dashboard ammeter? I failed on my search for an explanation with pictures or drawings. Not confident with electrical modifications.

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/6 '67 Barracuda convertible, electronic ignition, 4-OD, street cam, SBP KH discs, 3.55 SG 7.25" 1" t-bars. Bilstein.
340 '67 fastback, Doug Nash 5-speed.
1988 Toyota pickup work truck

First; disconnect the battery.

Second; make sure the battery is disconnected.

Did I mention to disconnect the battery?

Reach up behind dashboard, and back off both nuts holding the two wires to the amp meter if you can access them. You may have to pull the gage cluster for easier access to remove these nuts fastening the conductors to the gage, as sometimes they will be rather hard to brake free.

Using a short bolt with lock washer & nut that fits both eyes of the two wires, bolt them together tightly, and carefully tape up the splice. Use plenty of a good grade of electrical tape such as “3M’s #33â€￾ so that it will never come in contact with a grounding source. If it dose go to ground, you will have a fire under your dash, and will not be able to disconnect the battery fast enough to limit the damage.

One of these wires is directly connected to the + side of the battery, and may or may not have a current interruption device in line… In other words, someone may have removed the fusible link so that you now have a 10 gage wire from the + side of the battery, and potentially it could go directly to ground, making a lot of hot copper, if not taped up properly.

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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

Should I disconnect the battery, first? That would take the ammeter out of the circuit, but is there still a lot of current going through the bulkhead connectors? Or does taking the ammeter out of the circuit lessen the current in the system. Yes, I really don't know much about auto wiring.

When modifying a circuit, make a drawing and post it in the forum and get comments on it, unless you have the knowledge of exactly what you are doing. Many cars are lost in fires because of that.

I will comment a little on the protection of an electrical circuit. many cars and trucks have very little protection in stock form, and especially when upgrading the alternator and/or expanding the circuit with new additions like a radiator fan, heavy stereo or extra lighting, it is absolutely necessary to upgrade the components in the old circuit. There is a difference in the wire harness for a car with a 35 Amp alternator and a new heavy-duty 140 Amp alternator. Protecting the circuit parts with 'fusible links' and/or fuses should be a natural part of an upgrade. Personally I can't stand 'fusible links', but they work and many people prefer them over fuses.

Glass fuses (3AG type) are available as AGC (Fast Acting) and MDL (Time-Delay) fuses, the time-delayed fuses may in many cases mimic the fusible links. They are available in sizes form 1A to 20A.

The standard blade fuse ATO and ATC are fast acting blade fuses, very suitable to protect electronic and instruments, but is also the most used type today as a general fuse. The wire in ATO is open to the elements, the ATC is closed, and is therefore preferred in places where petrol fumes or gases may ignite. The are sized from 0.25A to 30A.

The Maxi-fuse is a blade fuse with some time-delay, and is what I think is a good alternative to many 'fusible links', sizes from 30A to 80A.

The Midi and Ami is as far as I know only product names for the same type of fuse, sizes from 30A to 200A.

I am going to use at least one of these fuse blocks that combine two different kind of fuses, under the hood of my Aspen to feed different sized circuits for charging, horns, ignition, lights and radiator fan, and the feed to the fuse box inside the passenger compartment. I think there are at least 6 'fusible links' to the wire bundle going through the bulhead.

Slantfin, I suggest you take some time to use the search function, there is an amazing wealth of infomation in this forum!

Olaf.

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Aspenized

Slantfin:
[quote]That would take the ammeter out of the circuit, but is there still a lot of current going through the bulkhead connectors?[/quote]

You bet there is, still the same current (flow of electrons) as before the amp meter was removed. This circuit is the main feed to all the electrical components in your car. It has two paths, one from the battery, and the other from the Alternator.

Get out your “[url=http://www.mymopar.com/index.php?pid=24]Wiring Diagram[/url]â€￾, trace back from Amp Gage to battery. The red wire passes through the bulkhead connector, hopefully a fusible link or equivalent at that point, to the starter relay, and than to the + battery terminal.

Now follow the other terminal from “Amp Meterâ€￾ to a splice where current is feed to Ignition, Head Light switch, and back to Alternator. There will be two wires involved, a black & brown.

Where the amp meter is positioned between the battery, and alternator it can read current flow from the battery to the “Loadâ€￾ (stuff needing electrons to operate; radio, horn etc.), and current flow from Alternator to “Loadâ€￾

When only Battery is supplying current, the meter points left to “minusâ€￾.

When only Alternator is supplying current, the meter points right to “plusâ€￾.

When both are contributing, the gage will show which is supplying the greater amount of current. Generally the alternator has greater flow, as this is how the battery is charged, and why the gage usually points to + when engine is running at a high enough rpm to generate sufficient electrical energy from the alternator.

Once the meter is removed, the circuit remains the same, except there is no way to measure direction & quantity of flow of the electrons.

Kind of like removing a window from a wall, the wall is still there, just can’t see through it any more…

Do as Olafla suggests, draw out this circuit as you trace it from the diagram, labeling the "Gage" (rather its size; lower number = thicker wire), and color of the wires as you go. Keep it simple. Than find these wires & their connections in your car.

Hope this helps.

Bill

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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

I appreciate the info, wjajr and Olafla. I'm a bit encouraged by having been able to find some short circuits recently and repair them. I even have a soldering iron now that's suitable for small wires. First thing is getting the cars on the road, but next summer I'll address the design weaknesses in the wiring system, including relays for the headlights. Just gathering information at this stage.

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/6 '67 Barracuda convertible, electronic ignition, 4-OD, street cam, SBP KH discs, 3.55 SG 7.25" 1" t-bars. Bilstein.
340 '67 fastback, Doug Nash 5-speed.
1988 Toyota pickup work truck

Then you're on the right track. slantfin! Go step by step, study the schematics, make a plan and a drawing, let it lay for a while before you revive it and find the flaws in your plan, and THEN you can go to work, step by step. If you don't have one already, buy a multimeter. You don't need an expensive one, the cheap ones have the basic features you need. What you will use most is the voltmeter, an ohmmeter to measure the resistance, and a test-lamp feature - a beeper to indicate contact between two points. It won't take long before you become an expert in tracking bad connections!

Olaf.

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Aspenized

Just an observation:

I had problems with my 77 D100. First I thought I got a bad battery, then thought the alternator was shot, then I replaced the starter relay then I thought it was the starter itself, read about the HEI conversion and the shunt, etc...

I searched these pages and did all the diagnostic work and was coming up with a-ok on all components. Still having problems tho.

I came across something about the charging circuit and the ammeter and replacing, bypassing, shunting, etc...so I checked this myself and realized what a critical circuit it is. I had some problems with the ammeter and the wiring in the back was coroded. It looked like it might fall apart if I disassembled it so I just gooped it up with dialectric grease and called it a day.

Long story short after realizing its importance I took the dash off and disassembled and cleaned the connections, and gooped them up and reinstalled them. I had a 2" burn down the red wire insullation that I taped up, later to be replaced with a -gulp- splice. I was going to bypass the meter, but Dan basically called anyone doing this a sissy. so now the truck runs fine and I think that was my problem.

The electrical systems on my truck worked fine in 1977 and should work fine today. Yes they age and need maintenance and repair. But don't think that switching to HEI or replacing a relay or putting in a shunt is going to fix the common aging problems. Go through the systems that Mopar gave you and make then work right.

If you want to upgrade, upgrade from a well working system, and upgrade for a reason; more accessories, bigger sterio, drag racing, etc...and upgrade all the parts that need to be.

I don't plan on adding or changing anything in the electrical department besides replacing a stock radio with another stock radio (that works). So I keep an extra ballist resistor in my glovebox and run it stock. i don't think there is anything wrong with this now, let's see how it works out for me.

Kudos to Aggressive Ted for clearing my head on the HEI quandry. That's a nice car you got there, mister.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Ed:
Well that is what I was trying to simplify by implying one or the other device was not working. Direction of current if either the battery was not putting out any current (in other words flow was to battery from alt.), or alternator not putting out any current (or battery was causing all current flow) which way the gage would read.

Third statement was to make clear that the current can flow in either direction depending on output or condition of battery & output of alternator. Guess I wasn’t too clear.

I stayed away from regulation of current so as not to muddy the waters any more than I have all ready...

Too bad one couldn’t graft in a Prius current flow screen like device with the stupid little arrows. LOL But I guess that is what the gage dose if one understands the electrical system.

Bill

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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