Installing a Mechanical Boost Gauge, 4 Wires? Options

[JoKeRkId613]

I've previously installed a boost gauge with 2 light wires (pos + neg). I wired the positive to the positive illumination wire and the negative to the negative illumination wire so they dim with the rheostat.

Now I'm installing a boost gauge on my friends car with 4 wires. They are battery(+), engine ground(-), 12v ignition switch(+), 12v ignition switch(+). So I'm going to guess the battery and engine ground would go to the positive and negative illumination wires respectively. Can someone confirm this? OR are these not "dimmable" gauges?

Can someone tell me what the two positive ignition switch wires are for?

Thanks in advance.