Hey guys, Trying to wrap my head around bypass type wiring for a Ford inductive ammeter. I am wiring a '50 Ford from scratch, changing to 12v neg ground. Using a standard 10SI alternator. Do I run the normal wire from alternator to battery, and then also from alternator to main junction (main junction in this case is the ignition switch itself) and from main junction through the ammeter loop to the battery? Or do I need to run the feed from the alternator to the main junction, then two wires from the main junction to the battery with only one of them passing through the ammeter loop? I've done a whole lot of wiring harnesses, but virtually all of them that weren't bone stock factory reproduction deals have used volt gauges. This is just one thing I'm not so familiar with. Don't know why I can't figure it out in my head..
Boy howdy you don't ask easy question at midnight. Especially after I had a couple of drinks at my 60th Class reunion. This is a one size fits all diagram for an idiot light, ammeter or volt meter and shows how each hooks up. With the inductive gauge you just run the wire through the holder for a lack of a better term on the back of the gauge and on to the battery or terminal that connects to the + post of the battery provided it is negative ground. The magnetic field flowing through the wire is what moves the needle. The good thing is that although you may peg the needle you can't overload the gauge with the amp flow as with one that the power actually flows through the gauge.
Made a couple alterations (crudely) to the diagram. With an ammeter all the electricity going to or from the battery should pass through the gauge. Also the voltmeter should be on the load side of the ignition switch otherwise it will be a constant load on the battery even when off.
I would make an additional alteration to your alteration, in that the red wire from the alternator side of the ammeter should go to the opposite side of the switch rather than the load side. My question was purely in regards to running a parallel wire with the ammeter like some folks do when running a lower amp scale gauge with a higher output alternator. I just didnt know if it worked the same with an inductive ammeter as it does with a normal one.
I changed my ‘42 Ford PU from 6v generator to 12v 10si. I just ran the wire through the ammeter, now I only had lights, ie no radio/heater etc. I had mine set up like a 1-wire, I ran a wire to a bulb I put in the dash Start the truck and the light would be on. Let the 221 warm up, take it up to around 1000rpms and the alternator would start charging and the light would go out. Worked for me, but I wasn’t using creature comforts in the truck.
That's not the way ammeters were wired in old cars. The way it is wired it will show charging current, but not any draw from accessories. It should be wired in the short section of wire coming off the positive battery post. That way you will see both charging current and current draw of accessories. In fact, power for the ignition switch should be moved past the junction going to the load. I used an old Ford inductive ammeter when I wired my Model A. My alternator has a higher current output than the ammeter reads. So I ran 2 wires in parallel, one goes through the loop on the ammeter and the other outside the loop. That cut the current going through the loop in half so the meter doesn't peg out all the time. It works just fine and will tell me that a low idle with the headlight on, radio on and heater blower on high, there isn't much current going to the battery.
Maybe it is the way the original drawing was labeled; but I took the right side of the switch with the alternator energizer and indicator light as being the "on" side of the ignition switch and the "load" being the stuff like the lights that are not ignition switch controlled. You would want that stuff wired to the "car" side of the ammeter to show any draw. On the parallel wire, @Kerrynzl has posted info on using a diode in the parallel wire to keep the ammeter accurate and protect from overload. Maybe not as important with an inductive meter; but with everybody using high amp one wires now-a-days it is something to keep in mind.
That is exactly what I needed to know, thank you! I am going to wire it with an 8ga charge wire going to the post on the IGN switch, then two 10ga wires from that post to the Batt terminal on the starter relay, with only one of those wires passing through the loop on the ammeter. That will make me feel better about the off the shelf harness only having one 10ga wire to feed everything anyways, no chance of being undersized with two 10s.
Yeah actually now that you mention it, that original drawing doesnt really make sense in a number of ways... I think we are on the same page, its just a bad diagram to start with. Or to charge with.
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