battery voltage is pretty easy, I assume they share the common ground of the vehicle so you will need just 1 wire from the + on each battery to each gauge(battery isolator will have both of those), and then ground each gauge locally, BUT.............
Battery gauges do draw power, not much but not 0 either.
So I would use either 2 relays or one dual pole relay on the + wires.
Relay power can be from any "key on" fused circuit, relays draw less than an amp so any fused circuit can be used.
That way voltage gauges are disconnected when key is off.
And remember "battery" voltage is when key is on and engine is off, after engine starts there is no more "battery" voltage, the alternator is now powering the system at minimum 13.6volts
Ford stopped using Oil Pressure Senders in mid 1980's, they have an oil pressure switch now, below 6psi is OFF, above 6psi is ON.
Depending on the gauge you have purchased you will probably want a PS60 oil pressure sender, google it, it is a universal oil pressure sender.
Your current oil pressure switch should be near the oil filter housing, you will need to unscrew that, and take a picture of the room around the hole it came out of, and then go to auto parts store and get a PS60 to see if threads on switch and sender are the same, if not you will need an adapter, also check if you have the room for the PS60, it will be larger than Ford switch.
To keep original Ford gauge and "oil light" working many use a "T" fitting so BOTH the Ford switch and PS60 can be used on that same hole.
Oil temp is tough to add, you really need to read the oil temp in the oil pan, you can pull the oil pan and drill a hole low on the sump to install a temp sensor.
Or if you have access drill the hole with pan in place, make sure to flush out all the metal fillings.
There are oil Drain plugs that have oil temp sensor built-in, with detachable wire, these do work although on some drain plug locations I would worry about the wire sticking out, lol.
Oil pressure and oil temp both need their own wires to the gauge, oil sender just needs the 1 wire since it is grounded via the metal fitting to the block, temp sender would be best with 2 wires, but depends on the temp sensor you use, some are chassis ground(like PS60) others have 2 wires coming out of the sender.
Both are powered at the gauge, you may want to add a fused circuit of your own for this, Key On of course, but an existing fused key on circuit would probably work OK, if fuse blows you can always add your own circuit then.
Last edited by RonD; 08-10-2014 at 12:20 PM.