Help with Ammeter Shunt Location / Power Junctions

Interior and Electrical

  1. cal30_sniper

    cal30_sniper Member

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    Hello all,

    I'm getting ready to swap in a roller V8 in place of my bare bones slant six, and will be upgrading the charging system to the 90A Magnum alternator to support electric fans and other power needs. While I've done charging system upgrades on GM products before (which is as simple as replacing the battery cables), I've never dealt with an ammeter or fusible link wiring before like the Mopars have.

    I realize our cars have a shunted ammeter. My Factory Service Manual shows a 6GA cable between the positive battery post and the junction with the ignition/headlamp switch power, with a 10, 12, or 14GA wire continuing on from that junction to the alternator (mine should be a 14GA wire, as it has no power accessories or options). Somewhere between the battery and this power junction, are the two 20GA wires that come off and go through the bulkhead to the ammeter (which is the shunt type).

    So now my questions:

    1. If I run a new 4GA cable from the battery to the alternator (what the Magnum vehicles use), can I relocate the 20 gauge shunt wiring to that new cable to keep the ammeter operational?
    2. If #1 is possible, would I also need to relocate the Headlamp/Ignition Switch junction to the new cable, on the alternator side of the shunt splicing? (this would basically be replacing the entire 6 & 14GA factory cable with a 4GA cable.
    3. Where is the shunt wiring junction physically located, and what does it look like?
    4. Where is the headlamp/ignition switch junction physically located, and what does it look like?

    I'd really like to keep the ammeter working. I realize it's almost pointless, but I like it. And I don't like the thought of a nonfunctioning gauge (I already have a voltmeter installed in the rear-window defrost switch location).

    Has anyone ever done the "Big Three" charging system upgrade to an FMJ, and is there anything else I'm missing here?

    Thanks!
     
  2. cal30_sniper

    cal30_sniper Member

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    Looking at the wiring diagram a little further in depth, perhaps the best route is just to leave the factory cabling hooked up as designed, including the 14GA wire to the alternator, and just add an additional heavier gauge cable from the alternator back to the battery. I think this might prevent the ammeter from working properly, but the resistance of the ammeter is probably calibrated for the 6GA cable it's currently shunted to, so I doubt it would work properly if I shunted it into a larger gauge charging cable either.
     
  3. 69-

    69- Well-Known Member

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    You would need to protect that direct alternator to battery cable (eg one size smaller fusible link). And you better add a voltmeter - because the ammeter will meaningless.
     
  4. cal30_sniper

    cal30_sniper Member

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    The alternator charge wire will be on a high-amp fuse just like the factory magnum motors were. I’m not a fan of fusible links, but agree that something is necessary there.

    “I already have a voltmeter installed in the rear-window defrost switch location”

    I’m not really interested in debating the merits of the factory ammeter. The information it provides is better than a hole in the dash. I currently have both, and would like to keep it that way.
     
  5. slant6billy

    slant6billy Well-Known Member

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    If the original engine harness for the slant is in good working order, reuse it. Upgrade of the charge cable to the battery is not a bad idea. The 2 field post on the magnum alternator will hook to the original slant's voltage regulator circuit. There are a bunch of Jeep folks running a mopar voltage regulator (firewall mount type in any F body). When I joined a van forum a few years ago, the van guys were doing a separated voltage regulator outside of the pcm. It was a firewall mounted mopar type too. I've seen folks go to the "one wire" chevy Summit racing charging circuit and alternator. It works, but local part stores might not be able to get replacement pieces as easily as stock mopar gear. Like with any 40 year old mopar, keep a few voltage regulators, ballast resistors, caps, rotors in a shoe box in the trunk. Cheaper than a tow truck.
     
  6. Mikes5thAve

    Mikes5thAve Well-Known Member

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    If your amp meter moves much count yourself lucky. Most stay in the middle area and don't tell much of anything even when there is significant charging or discharging going on. I've never replaced mine because having a gauge that doesn't match the rest is almost as bad as having that hole you mentioned.
     
  7. Duke5A

    Duke5A Well-Known Member

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    What electric fans are you swapping in? I ask because 90 amp might not be enough. I've got the dual Ford Contour V6 fans on my 26" radiator - fit good.

    I thought about trying to rehab the charge gauge, but you're right, it's calibrated for the charge system if it even does work. I pulled out all the wiring under the hood to clean it up and used a single wire Power Master alternator with 4 gauge wiring back to the battery with a circuit breaker for protection mounted on the driver's inner fender.

    It does bother me having a useless gauge in the cluster. I've seen guys fit new gauges in place of those pods and make it look factory, but I'm not that talented.
     
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  8. cal30_sniper

    cal30_sniper Member

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    I’ll definitely be keeping the external voltage regulator. I already converted it to a relay controlled field wire and it works great. All I’ll need to do is hook up the two field wires to the terminals on the Magnum alternator.
     
  9. cal30_sniper

    cal30_sniper Member

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    It’s a single Taurus fan with a Volvo Relay. Should only draw 30A on full speed. I have a small amplifier for the stereo, but it maxes out at 40A and I never push it that hard. No A/C, no power accessories.

    Because it’s a non-A/C car, I only have the 22” radiator core. I pulled the 26” core plates out of an M-body, but I really don’t want to do that much surgery on my car. Instead, I plan to use a ZJ Grand Cherokee radiator. It’s a 22” wide core with side tanks instead of top/bottom tanks. The Taurus fan fits the core very nicely, and the brackets should be easy to adapt to use the factory ZJ fan shroud mounting setup. Overall cooling surface area and volume are nearly identical to a 26” truck radiator. It’ll take a little fab work, but I think overall it will fit very well, and has the large trans cooler fittings for the 46RH I’ll be running behind the 318. As an added bonus, I got the factory trans cooler and all the lines back to the trans from a ZJ in my local yard. It was also the donor for the Magnum charging system and starter.

    Lest anyone reading this in the future get confused, I’m using the passenger side starter 46RH from a ZJ Jeep. This allows me to run the ZJ magnum exhaust manifolds, which flow far better than factory LA manifolds. They also clear the firewall and column shift linkage, unlike the driver’s side Ram/Dakota/Durango/Van manifolds. The Jeep 46RHs only came in 4WD, but I had my core rebuilt with a 2WD OD housing and tailshaft. Anyways, that’s a long way of saying don’t go blindly buying Jeep stuff, because most of it is different to support the passenger side starter.
     
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  10. Hayzoos

    Hayzoos Well-Known Member

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    1. It would be operational technically, but it would move even less than it does now. The movement may be barely perceptible. There may be a way of making it work better though.
    2. Yes, the ammeter circuit needs to be tied to the main wire where almost all electrical loads are fed.
    3. & 4. I do not know for sure, but referencing a Haynes manual wiring diagram it calls out left front wheelhouse (aka inner fender) for headlamp/ignition switch and I guess the shunt wiring junction would be closer to the battery. It will be a wire splice (welded/soldered?) probably inside of the harness between the fusible links that go into the bulkhead connector and the 6GA wire to the battery.

    Ammeters are actually a volt meter with the zero at the center of the range and it reads both positive and negative. A shunt of adequate gauge for the current and specific resistance is wired across the ammeter terminals. The meter is reading the voltage drop positive or negative to indicate current flow (charge or discharge) thanks to OHM's law the amount of current can be determined by knowing the resistance and measuring the voltage. All wires have a certain amount of resistance per measure of length, so a longer wire has more and a shorter wire less. Wire gauge also affects the resistance, larger diameter wire has less and smaller diameter has more.

    The Haynes manual wiring diagram I am referencing is labelling the 6GA wire as the shunt. I see also the 20GA wire you referenced. The wires under the dash to the ammeter are 16GA in my reference. Finally, the meter is mounted on a circuit board with traces for conductors whose resistance has to be accounted for. All these wires/conductors together make up the shunt in reality. All the wire lengths have to be specific in order to have a known resistance.

    To make the ammeter work better requires altering the resistance of the shunt. You propose making the primary current carrying wire between the battery and the alternator less resistant by going with a larger diameter. Don't forget length matters, it has to be just right. In order to compensate, you have to lower the resistance in the circuit where the 20GA and 16 GA wires are by shorter wire (not feasible) or heavier gauge. How much is the key. I could figure it out, but lack of time and suitable testing environment prevent me from doing so. I would probably approach it by testing the ammeter to see how much voltage deflects the needle by how much and record the results. Then I would measure the resistance of the ammeter circuit at multiple points. I would then measure voltage across the ammeter while also measuring current draw to have numbers to double check calculations. I could then calculate what new resistance I should strive for to "improve" the functionality of the ammeter.

    I do want to point out a few things to consider. Just upgrading the alternator to battery 6GA wire to 4GA is incomplete. The current flow is in a complete circuit. You would be improving the situation somewhat, but what about the return path? I am talking about the battery grounds, specifically to the engine for charging since the alternator grounds to the engine. For the most bang for the buck you would want to upgrade those ground wires to 4GA as well. If you look further, you may notice the starter wire is also "only" 6GA and wonder how that can be since batteries are rated at hundreds of cold cranking amps. A starter is typically run for short durations so overheating the wire is not as likely, a 6GA wire will handle the task.
     
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  11. Duke5A

    Duke5A Well-Known Member

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    OK, now that is just clever.
     
  12. cal30_sniper

    cal30_sniper Member

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    Agreed. I may just take the easy route and supplement the current charge cable with an additional 4GA charge cable straight from the alternator to battery. As you mentioned, I will definitely be upgrading the grounding cable as well, both for the battery and the alternator. Most of this will use factory Magnum wiring that I pulled from the junkyard. I'm less concerned with the starter, but will likely upgrade it as well just to get the factory fittings for the new Magnum mini-starter. Since it's moving to the passenger side, I've got to redo everything anyways.
     
  13. cal30_sniper

    cal30_sniper Member

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    We'll see if it works! Trans is getting here today. Next up is swapping the 302 heads for some LA-pattern Magnums and throwing in the new hydraulic roller cam. Then I'll start fitting it all to the M-body crossmember and figure out what trans cooler lines and oil filter setup work best with the new exhaust and trans. I'm hoping to use the ZJ headpipes as well, at least until I can get it to an exhaust shop for a proper system, but I'm not sure how frame clearance is going to look. I have similar concerns with the trans cooler lines, but also pulled a set of A518 lines out of a 92 Ramcharger that run down the driver's side in case there's interference. I'll start a swap thread once some useable results start popping out.
     
  14. Aspen500

    Aspen500 Well-Known Member

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    Not the same setup but for what it's worth,,,,,,I used pre-bent lines from Inline tube on my BB Aspen (for a late '60's B-body) and they run down the drivers side just like they belong there with no modifications other than the obvious near the radiator. I'd think drivers side lines would fit even easier with a small block.
     
  15. cal30_sniper

    cal30_sniper Member

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    Thanks for the info. The M-body I parted out (318/904) had the 5/16" driver's side trans lines. I also parted a 92 Ramcharger (360/A518) that had 3/8" driver's side trans lines, and a '94 Grand Cherokee (5.2Magnum/46RH) that had 3/8" passenger's side trans lines.

    On the Jeep, the lines cross over to the passenger side between the oil pan and trans bell housing inspection plate, then run below the passenger side starter and oil filter to the trans cooler fittings on the passenger side tank of the radiator (they are vertically oriented in the side tank, as opposed to horizontally aligned in the bottom tank like other Mopar radiators). As long as they clear the M-body V8 crossmember, these are the lines I want to use, as they give me the most amount of exhaust clearance on the driver's side. I may have to use the Ramcharger lines if the Jeep lines interfere with the front crossmember, but I'm fairly certain the Ramcharger lines are going to run right through where the driver's exhaust headpipe needs to go for the Jeep manifold.

    I'll need to use the 3/8" lines of one type or another, or fab my own. All A500/A518/42RH/46RH trans came with larger 3/8" lines for improved cooling. I'm trying to get away with using as many factory parts as possible for this thing.
     
  16. BudW

    BudW Moderator Staff Member

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    In some years, cars/trucks with the towing package, came with 3/8" metal lines. The problem then was the adapters (transmission and radiator side) were the same ones used with 5/16” lines as well as the cooler itself was the same side. The plus part of 3/8" lines, is at least it holds a smidge more fluid.

    For whatever reason, Chrysler changed the transmission cooler lines and mounting/mounts for the lines every one to two years. If you have a complete set (no matter from what year) – it will work. Mix/matching parts from different years is hit/miss (more on the miss side).
    That said, there is a bit of change between the A904 series (and OD variants) vs. the A727 (and its OD variants) - but either can be hand bent to fit each other (in most cases).

    One major change was in '79 (or '80) when they went to a short piece of rubber hose to attach the lines to the radiator. The rubber hoses did a lot to prevent the metal lines from cracks (from the vibration and from engine movement) – but created a new mess with rubber hoses leaking under pressure. On vehicles with lockup converter (mid-year '78 change), the transmission cooler line line pressure went from 20ish PSI to 80-100 PSI when in lockup mode. Those rubber hoses will seep fluid under that much pressure which makes a mess.

    Either version (with or without rubber hoses) still have the problem of line rub-through – so make sure the lines are not positioned in a place where there is line contact to anything (cooler line to each other, from oil pan rail/bolt, K-frame, side of transmission, and so forth). To take some time and make sure there is no line contact – will prevent a major fluid loss down the road (ie: leave you stranded on side of road with a vehicle with no ATF, somewhere).

    The cooler lines on my '77 Volare, travel to passenger side of engine then straight to the radiator (on the passenger side).

    The rubber hose style fixed a ton of cooler line cracking problems I've had to fix over the years (ie: TONS), so I like that feature. The rubber hose leakage - I could do without. Rubber hoses do not do that well under that much line pressure, long term.
    BudW
     
  17. cal30_sniper

    cal30_sniper Member

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    Bud, about the only thing you can try and do for the rubber hose leaks is install fuel injection style band clamps. They seal a lot better than the old worm gear clamps those hoses typically came with.

    Next step up would be to install compression fitting adapters (or cut and flare) for braided AN hose. That absolutely won’t leak if done right. I did that (with 1/2” lines) on custom trans cooler for the 6L90 in my 750hp semi-daily (had to move around all the factory coolers for a custom intercooler setup).

    Believe it or not, 3/8 lines are still a huge improvement in flow over 5/16 lines, even with the smaller fittings. Like electricity, fluid resistance to flow is highly dependent on length of the restriction. A very short piece of 1/4 or 5/16 diameter is far less restriction than 4-5 feet of 5/16 diameter.

    However, the nice thing about the factory A500/A518 setups is they have the larger diameter through. Fittings, lines, coolers, and aux coolers are all 3/8, which leads to superior flow. Only thing better is the Cummins setup with 1/2” lines, but it’s quite unorthodox due to the block mounted heat exchanger between the trans and radiator.
     
  18. BudW

    BudW Moderator Staff Member

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    My '94 Cummins pickup had 1/2” transmission cooler lines with factory “QUOTE“ quick disconnect fittings on the transmission side. Quick disconnect my ___ (fill in the blank), for it was a royal pain to disconnect. Most of them use plastic inside of the fitting. Using a Cummins like one should (ie: hard), the automatic transmission (more specifically, the torque converter) gets very hot when pulling a load or going uphill. The plastic in those quick disconnect fittings would melt (imagine that) which will cause a large leak when in lockup mode – OR worse, would allow the cooler line to come completely off causing a very quick loss of transmission fluid leaving you stranded in a very short time frame. At least Chrysler used larger fittings on those pickups and it wasn't too hard to make new lines with normal fittings. It wasn't until 20 years (or so) of using Cummings before Chrysler started to use a full metal disconnect fitting at transmission.

    One thing I don't understand is using plastic where heat is involved. Using plastic on mechanical, cooling or other heat related parts equals one result (...a premature failure). Well, I do understand getting the weight down for fuel mileage reasons and for costs – but still.
    At least make a (full) metal replacement part as an option (like thermostat housings, oil coolers, oil pans and covers, and so forth).
    Then, don't get me going when companies install a turbocharger(s) about 2 inches away from a plastic valve cover without any heat protection (sigh).
    BudW
     
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  19. Duke5A

    Duke5A Well-Known Member

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    If you want hard lines then NiCop is the way to go. Very easy to bend and it doesn't rust. I used 3/8" for my fuel system.

    Other way to go is use braided PTFE hose and fittings. The PTFE stuff is on an order of magnitude easier to work with and the line will never deteriorate. AN fittings are pricey though.
     
  20. Duke5A

    Duke5A Well-Known Member

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    My 1992 F150 uses quick disconnect for the fuel lines and while the retaining tabs are metal, being in Michigan means rusted in place. I hate QD fittings.