![]() With continuity and a little voltage your ammeter should be working. ![]() (Its not purple in real life, black and yellow actually, but since its covered in black tape you can't really tell that.) The voltage won't be much but you should measure a few millivolts. With those wires reconnected use your meter to measure voltage across the 'purple' wire shown in my drawing while you are discharging some current such as with the headlights turned on. If that measures OK then the meter may work when you reconnect the red and yellow wires. The reason to disconnect the red wire also is to make sure it is making good contact with the solenoid connection when you put it back together. Actually you only have to unplug the yellow wire and measure from the yellow wire back to the end of the red one. I would start by disconnecting the red and yellow ammeter wires near the solenoid and using an ohmmeter to see if there is continuity through the ammeter it should measure less than an Ohm. It would take about a week for that to run your battery down but that's still adds a hassle factor most of wouldn't want to put up with. You would still want to hook it up to the ignition switch since a full scale reading on a fuel/oil/water temp gauge draws nearly 1/4 Amp of current. Something like a fuel gauge will fit in the ammeter hole and that would be a whole lot easier to turn into a fairly good voltmeter although the scale markings would still be a bit odd. A good voltmeter shouldn't draw much more current than your clock so you could probably get away with wiring it like I mentioned above. That would cause your battery to go dead every day if you didn't drive the car. With the stock meter that means you would be drawing 2-3 Amp all the time if you want a meter needle pointing over towards the right side of the gauge. If you want a voltmeter it really should be wired through the ignition switch or else you will be drawing battery current all the time. A 'Better Idea' - at least for the bean counters. They got to have a tach option and, except for the Rally Pac itself, added absolutely ZERO extra wires to the cars to be able to do it. Its sort of like the trick they used of wiring the Rally Pac in series with the ignition switch. Its ALWAYS working its just that when the car is off there is nothing to measure. Also, by this trick they didn't even have to worry about hooking the ammeter up to the ignition switch. A real ammeter would need 80x times bigger wires which cost money, are heavy, big, etc. The reason Ford wired these so squirrelly was to save some pennies on wiring. That doesn't hurt anything else in the car so few ever take the time to figure out there is even a problem with the wiring.Įlectrically this is called an 80:1 shunt circuit. On many cars, the connection at the solenoid end of the red and yellow wires are dirty or broken and there will be NOTHING going through the ammeter. Neither 230 or even 100 A will ever happen with the stock alternators which explains why this meter needle never moves a whole lot even if it does move. Unfortunately, full scale deflection of the ammeter takes about 2.8 A so that means the charge rate at the upper end of the ammeter scale is almost 230 A. About 1 1/4 A, or 1/80 of that charge current will go through the wires to the ammeter if all the connections are good. ![]() I give example numbers for an alternator charging 100 Amps into the battery. The ammeter coil itself is about 1/6 Ohm but when you include the red and yellow wires to and from the purple wire the total impedance for current flow through the ammeter wiring is right at 1/4 Ohm. The 4-way wire connection down by the alternator is a thick lump you can feel inside the taped harness, its not anything you can actually see without removing some tape. These wires are all wrapped together inside the underhood harness so you have to scratch your head a little while to figure out where these all are and how they connect. ) The little rectangle shown in the middle of the yellow wire by the solenoid is a connector built into the wiring harness. (Its actually a black/yellow wire but that's hard to draw. The ammeter is actually reading the voltage across what I drew as the big purple wire in the drawing. The lengths given for those wires includes the wire on both sides of the firewall. The red and yellow wires go through a connector in the firewall which I have not shown to keep the drawing somewhat simple. I have only drawn the wires involved in the ammeter circuit and given their colors and size/length where appropriate. The attached JPG shows how the ammeter wiring in a factory 1966 harness works. I have waved my hands to explain this one several times so I figured it was time to make a posting of exactly how it all works. ![]()
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