In my sketched diagram below the amp gauge on the left shows how I wired it years ago. (I believe incorrectly). Everything worked fine, but I've recently discovered the generator, lighting, and horn circuit was not on the fused terminal of my amp gauge which it should have been. The other two terminals are not fused. The amp gauge has the fuse holder built into it. The sketch on the right is how I think it should have been wired according to the oem Mopar wiring diagram. But, it originally had a cut-out relay on a generator. I converted to 12v an added a 1970s Mopar alternator with electronic regulator which also has been working great for years. So, if I hook it up like the gauge on the right I will be running the newer charging system thru the 30amp fused circuit along with the lights and horn. Just not sure if that is a good way to go? The lead from my harness going to the amp gauge has three wires (generator wire, horn, and headlamp switch) all on one connector. I could change just the alternator wire from the fused terminal and connect it to a non fused one. If a short occurs in the lighting circuit then the alternator would not charge. I am electrically handicapped. Advice welcomed!
I'm sure you have considered using a voltmeter instead of the amp gage. Wiring is simple, just about anywhere you want, and hardly any current draw-unlike the heavy wired amp gage. An inline fuse or breaker of your choice and you're done. No potential for a "heavy" short like could happen with the amp., especially if in the dash, etc. Good luck. BTW, the 3 wires going to amp gage seems to be powered by the generator/alternator-horn and lights tag along for their power, tie 'em together and connect to the other side of the amp gage wire, complete circuit (series).
I would suggest a partial rewire, avoiding the ammeter. That alternator is rated three times the output of the original generator, and the ammeter would become a welding torch instead of a gauge if you hooked it up as per factory. What you can do is use it as a terminus- assuming you have the regulator wired correctly, the BAT terminal ideally needs to go to the starter lead, and from there a medium gauge wire up to the ammeter, where you connect that to the original GEN terminal, leave the BAT terminal disconnected and just power the car through the fuse as it was originally. That does mean the ammeter then does nothing; as said above you can replace it with a volt meter, which with an alternator is a much more useful gauge. Phil
Any way to use an existing Amp gauge as a Volt gauge? I hate to replace my stock amp gauge with a off-color/odd ball look'in Volt gauge. 6sally6
I’ve got a car that had an optional ammeter, but it would only work with the oem alternator and regulator. I refitted a volt meter internals behind it. With a full battery, key on, it reads 0. Start engine, it shows a charge to the first mark. Turn everything on (lights wiper, a/c, fan on high) it drops a bit, but shows a charge. If it goes below 0, I know it’s under 12 volts. Either shed load, or fix it. Really, that’s all you need to know. If you’re under the hood looking for a problem you’re going to be using a meter anyway. Depends on your oem guage, layout, etc. and what you can find in a new voltmeter. And how much you want to fiddle around. But a simple rewire, probably no.
What Vehicle? Just leave the Ammeter there. [Ammeters are connected "In-series" whereas Voltmeters need to be connected "In-Parallel" to ground] If you've swapped out a Generator for an Alternator, you can increase the range of an Ammeter . To increase the range of ammeter, you need to connect a shunt resistance in parallel to the branch where the ammeter measures the current. The biggest issue is not the ammeter, but the wiring each side of it. This should always be upgraded anyway with an alternator conversion. If you kept the alternator rating to around 40 amp there would still be an improvement over a generator because alternators still charge when idling. The ammeter can handle a 40 amp current [without a shunt] but you should upgrade the wiring. The most amp load on the wiring is just after an engine starts [we rev it up and the smoke escapes] 2 x 60/55 watt halogen bulbs only draw 10 amps on high beam. There should always be a fusible link between the Ammeter and the 12v source.
I'm hoping to keep the original ammeter, and the 70s Mopar charging system. I've been driving my truck for many years trouble free with the 60 amp alternator completely un-fused. Just recently, after thinking about it, realized I didn't know what I was doing then. (And,still don't) Rather than a fusible link, I'm thinking of adding a maxi fuse in the circuit with a 40 or 50 amp fuse? My original style 6v harness uses 10 gauge wire for this circuit which I believe is ample? I think this would protect the wiring and possibly the ammeter if the alternator hit max. output for some reason. Am I making any sense?
10 gauge isn't much! Just enough to feed 20-30 amps . In theory you need 4 gauge to handle a full 70 amps , so in all probability your alternator has never had to push this amount back to the battery. When you run the engine, heater, headlights, fan? simultaneously , very little charge actually goes through the Ammeter back to the battery [only for battery recovering from cranking] Most of the Alt charge is upstream of the ammeter feeding all the accessories and a running engine. If you want to leave the wiring as is, then run a 35 amp fuse [or circuit breaker] to protect this wire. And maybe hunt an early 60's Chrysler Alternator [ these are from 35 amps up ] My observations have been that after extended cranking the battery might draw 10 amps up to as much as 25 amps at the beginning of recharge. In a few minutes it will be down to 5 amps or less. It usually pays to let the engine idle for a few minutes if there has been extensive cranking.
Thanks for your advice! Very helpful. I did think about locating a earlier Mopar lower amperage alternator. The earlier ones (up to 1969) used a one field wire configuration. I don't think that would work with my 1970s electronic regulator? Referring to Rockauto, rebuilt alternators for 1960s Mopars with non electronic regulators are listed at 55 and 60 amps? 65 Dodge Dart with a 6 cyl. for example. That seems strange to me? Perhaps I've been lucky that my amp gauge has worked perfectly all these years? I'm definitely going to add the fusible link, maxi fuse, or circuit breaker. Am I correct in assuming that if for some reason the alternator were to reach maximum output, the fuse would kill the circuit before things start burning? Perhaps I'll add a fire extiguisher as well!
Maybe remove the ammeter gauge and run the a wire straight through to see if the gauge itself is causing something funny. I had what people are referring to above happen on my 57 with an added ammeter gauge. included dead battery, gen light coming on, when I got a a very,very hot gauge. I removed it, connected the battery wire to itself and covered it well. I have not had an issue of any type since. My Ford happened to have the GEN light though. I’m just saying sometimes the gauge itself can have issues.
Still a lot of misinformation about charging system gauges.... If you're running a generator, you want an ammeter. Alternator, you need a voltmeter. While both systems produce 12V DC and use the same basic electrical principles, their mechanical construction is totally different as is how they output power. Without going into a deep dive on the differences, a generator will maintain voltage output even if current output falls below what's needed. An alternator is opposite of that; it can maintain current output even when voltage drops too low. This is barring a total system failure. A partial failure like worn brushes on a generator or one or two failed diodes on an alternator won't show on the wrong gauge, so the wrong gauge is useless for monitoring charging system health which is the whole point of having a gauge. Fuses or other overcurrent devices installed on the charging system output are also a waste of time, particularly with an alternator.
@Crazy Steve The fusible link/circuit breaker is there to protect the harness, especially if there is a short circuit in the charge wire or main feed . Most modern cars has some sort of fusible link in the charging system [I wonder why? ] An Ammeter measures the flow of current to and from the battery. [an ammeter will indicate if the charging system is charging the battery, or if there is excess draw on the battery] A Voltmeter just measures the level of voltage of the whole system. Generally most plug-in garage battery chargers have an ammeter on them......Sort of makes you wonder why does it! This whole thread is about maintaining the integrity of the original vehicle [eg: keeping original gauges]
I stand by my statements... So let's take this in chunks... Yes, overcurrent protection is there to protect the wire, NOT the devices. So let's look at how you would size said protection. Now if you have a generator, it's easy; the typical generator only outputs 30 amp max and if you use a #10 wire for the output, it's rated at 30 amps so is high enough that no overcurrent protection is needed, it can withstand the full rated output even if the wire goes to ground. Not so with most alternators. The typical one-wire is 100 amps plus output. What size wire are you using for its output? Most harness kits only supply a #10, you may see as large as a #6 which is rated at 55 amps. I have yet to see anyone use a #1 wire which is actually rated for that current. Accepted practice for sizing overcurrent devices is 125% of the anticipated max current to prevent nuisance tripping, which in this case would be 125 amps. The problem here is the overcurrent rating is over double the wire rating, a recipe for a fire if a major fault actually happens. Truthfully, this would be unlikely. A far more likely scenario would be that any 'rubbing' short to ground would melt either the offending steel away (sheetmetal will melt rather easily when amps get above about 70) or more likely yet the wire strands would burn away one by one until the wire parts. This is why routing/supporting this wire to prevent physical damage to it is critical. If you can't manage that, you have no business wiring a car. That's only partially true. What an ammeter displays is the current difference between what the vehicle is using and what the charging system is putting out. If everything is working correctly and the battery is charged, what you'll see is a one or two amp 'charging' deflection on the meter. The alternator is carrying the full vehicle load, the 'extra' is the 'maintenance charge' for the battery. This does not tell you what the actual load/output in amps is. But be aware that this full load is present in the ammeter which is why using these old ammeters is so dangerous, or any ammeter that isn't rated for the actual full load. And somebody invariably brings up installing a shunt to increase the 'range' of the old ammeter. There's two issues with this. One, how can you be sure you've shunted enough current? You may still have a fire hazard. Two, increasing the range reduces the sensitivity of the gauge. That small 'charging' deflection will disappear and all you may see is the most gross changes, maybe not even those. Again, if using a generator a Ammeter is the right choice for monitoring charging system health. But for an alternator, you want a voltmeter. If you don't want to convert your ammeter and will leave it in the dash, just abandon it and install an unobtrusive idiot light and call it good. Different application. Not all batteries accept all charging rates.
The word "shunt" is a poor choice of words. Some people simply run a bypass wire from the Alt/Gen to the battery as a "shunt" [which renders the Ammeter useless] Using an actual shunt resistor also does this . @Steve Lowe The best way to try and use an alternator that has similar output to the original charging/ wiring system [that is why I suggested an early Chrysler Alt] Unfortunately most of these old Chrysler Alternators in parts stores are universal rebuilds which explains why they all have the same rating. I really helps to have the battery and ignition in the best condition so the engine starts easier without to much drain on the battery [over taxing the charging system] Normally the battery drain and initial recharge is fine as you have found out. [usually less the 25 amps] You can protect the ammeter from overcharging and/or over-discharging and still keep it working safely within it's normal operating range.
All the above advice, recommendations and opinions are greatly appreciated. I'm coming to understand why volt meters are a safer choice when running an alternator, but Detroit did produce a lot of cars with alternators with ammeters. I don't think they all caught fire. I am curious as to why parts suppliers are selling 60amp alternators for vintage vehicles that originally had 35amp alternators and ammeters? My truck is a resto-rod and I like the appearance of the dash gauges the way they were designed. Decades ago, I had a bunch of issues with my original generator / regulator and thought it would be cool to upgrade to 12v system with an alternator. I copied the wiring from early 70s Mopar with external electronic regulator. It has worked flawlessly since. Being much smarter in my younger days, I didn't give much thought to ohm's laws. I also neglected the fusible link that was in the diagram I used. I now understand that my 60amp alternator has the potential to cook my wiring, but as long as everything's working correctly, it only puts out what's called for. Barring any unusual circumstances that would call for full current, I doubt my system would draw even half of that with everything electrical on. Keep in mind the only electrical additions from stock are a radio, signal lights, and 9003 halogen headlights. After reading a bunch on here and another Mopar truck forum, it seems the general consensus is to at minimum, add a fusible link or fuse on the wire feeding the amp gauge from the battery terminal on my starter. I believe a maxi fuse the better choice because it would be easier to change a fuse if it blows. Although not a perfect solution, at my age I'm looking for the easiest way. If I get a short, I might be dead on the road, but the fuse (30 or 35amp) should protect the wiring? My other dilemma is where to fit the fuse holder? Not much room between the starter and brake pedal arm. Suggestions welcomed.
Hi Steve, If a fuse (say 30 or 40 amp) were added between my 60 amp alternator and the 30 amp ammeter, wouldn't that offer at least some protection from cooking the meter and wiring to it? If for some reason the system were to call for more amperage than the fuse installed, it would just kill the charging circuit? Other than a short, my truck would unlikely ever exceed a 30 amp draw. Maybe not technically a perfect solution, but perhaps better than not having any fuse in there? Am I making any sense? Also the ammeter in my truck is a robust unit built in the 1930s. It has a substantial buss internally connecting the two terminals and somehow works from sensing the magnetic field. I've attached a couple photos of a crusty one I took out of a scrap truck. Even the one in the photos in it's rough condition all the connections are good after checking it with a meter.
Without going into all the difficulties in fusing charging systems, I'll make few comments. One comment was the OEMs continued using ammeters after alternators were used. Yeah, they did... But with the exception of the first year or two of Chrysler using direct-read ammeters with their alternators (which proved to be prone to failure and occasional fires), they switched to shunt-type ammeters across the board. These weren't known to be particularly reliable either but had the one big advantage that if they failed, they did so quietly with little or no smoke and the charging system still functioned normally. And if you're REALLY trying to protect the charge wires between the alternator and the battery, you'll need four fuses. But let's ignore all that and just address what seems to be your main concern, protecting the gauge against catastrophic failure. I'll agree with you, it appears the internal buss in the gauge would withstand the possible current available under 'normal' conditions without issues. Whether or not the gauge movement will survive overcurrent is where the crapshoot enters into this, but even if it does fail I don't see it being a fire starter. I can think of multiple scenarios where alternator output could exceed the gauge 'rating' and if the movement fails you now have just a terminal block. So how to best attempt to protect the gauge? The big problem with trying to fuse charging systems is current can vary so much. You can see really big spikes sometimes, but they're usually of short-enough duration that wire damage doesn't have enough time to occur. Between the gauge and the battery I wouldn't worry about overcurrent protection as long as the wire is protected from physical damage. So that leaves the wire from the alternator to the gauge. Again, the generator isn't capable of outputting more current than what the gauge is designed for, so no fuse was needed. Not the case with the alternator, so an overcurrent device in-line on the alternator output is what you want. But which type to use? I'd start with a regular fuse, in a 35 amp rating as they're the fastest-acting type. Keep a stock on-hand as you may have nuisance tripping on a regular basis. If the frequency is too high, try a 40 amp but I'd be very hesitant to go bigger. If nuisance tripping is still an issue and the gauge is still working, second choice would be self-resetting thermal circuit breaker, starting with a 30 amp unit. These react much slower if the overcurrent excess isn't too much... but I would keep a spare handy as these do fail with too much cycling. You may need to go to a 35 amp unit if you see it cycling a lot. I would avoid a fusible link because of the hassle with replacing one. Personally, if I had a spare gauge, I'd take a shot at installing a voltmeter in it and eliminate the ammeter.
Thanks for your quick response and time you spent writing it. Attempting to convert or retrofit a spare amp gauge is likely beyond my capabilities and I no longer possess the patience to indulge such a project. Anyhow, after reading your comments carefully, I'm thinking I'm not totally off base? My latest plan is to get an MRBF block which will mount right on the alternator output terminal. This way, I can experiment with the fuses without cutting any wires. I have also installed a under-dash voltmeter made by Auto Meter. So if things go well with fusing without tripping problems, I'll have both amp and volt meters. If not, I'll take the ammeter out of the circuit. Am I getting a hesitant nod? I didn't understand you comment about four fuses?
You are. I won't guarantee the meter will survive, but I'm reasonably sure you won't burn your car down either. The only thing we're attempting to protect here is the gauge. That comment was to illustrate the difficulty/futility of trying to 'protect' charging system wiring with fuses or any overcurrent device. The key thing to remember here is to protect the wire, the fuse MUST be installed at the point of origin of the circuit. This was a major flaw in the older OEM harnesses prior to unified fuse panels. They tended to install any fuse at the device, which if the device failed would blow the fuse and save the wire. But if the wire went to ground between the point of origin and the fuse, it's now unfused wire and you'll get a fire. That's what makes those harnesses dangerous, especially if the insulation is failing and falling off the wire. The problem with charging systems is you have TWO points of origin; one wire from the battery and one from the generator/alternator and they'll tie together at a junction point or as in your case, an ammeter. Both wires can be fed from either end depending on the system operation or fault, so in reality both wires have point of origin at each end. So if you're trying to protect the wire, you need overcurrent protection at both ends of each wire. That's not the only issue with trying to fuse these wires either. If it's a real concern, install a NHRA-legal battery switch for protection. Fuses are unlikely to do what you think they will.
No resistor. My ammeter has 3 terminals. Only one of the terminals is fused (lower terminal in photos) originally with a 20A fuse. Only the lights and horn were attached to that terminal. A short anywhere in the lighting circuit would kill all the lights. In fact, that was the only fuse on the entire electrical system on my year truck.
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