Im in the process of rewiring a 53' mercury. Switching over to 12 neg ground. Which post on the back of the gauges do i give power to? I have a resistor to drop the power to 6 volts.
You want to use the same post that power was applied to originally. It doesn't matter that the polarity has changed, you still want the gauge hooked up as it was before.
If you get one of those Ford instrument voltage regulators, then no resistor is needed. Just look for one from 1956 up Ford Motors cars.
Those King-Seeley gauges don't care about polarity. They work on heat deflection caused by current flow. The gauges are designed to flow the most current at the point of the worst reading/ least used position on the gauge. Such as full on fuel because it is very rarely kept on full. Hot on temp gauges because if everything goes well the gauge will not hit hot, or very low oil pressure. Those gauges were used from Model A days up to 1986. From 1957 up they used a pulse 6 volt signal supplied by cluster/instrument regulator, often known as a CVS or IVR. Napa carries them and the one for 59 ford is the best one to use (B9A) because it has spade terminals instead of the later ones that had snaps so that the printed circuit wiring could be snapped onto it. If you need a replacement gauge, any later 12 volt gauge will inter change as long as the needle sweep is the same all that's necessary is to swap the faceplate and needle. When I was still doing rewiring on old Fords, I often substituted good later gauges for bad originals. The only exception might be the ammeter which used eddy current to read the charge/discharge as opposed to some later gauges that used a shunt. Simple, dependable, and Ford used a gazillion from 1928 until 1986. A real plus is the heat deflection acts like a damper on rough surfaces, since the gauge can't cool down or heat up as fast as the sender deflects. Magnetic gauges can deflect all over the place on rough surfaces.
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