Most of us have the Chinese repop gauges with a row of lights in the middle of the combo gauge that do absolutely nothing. The only functional one on my VS was the high beam indicator.
But you can put them to use simply enough for all sorts of handy tasks. I recently hooked up the two middle ones to the two fans I'm now controlling with under-dash toggle switches - the fan on the external oil cooler and a second fan I've mentioned here before that blows cool air through the firewall into the engine compartment.
Since I'm controlling these fans manually, it's nice to have a reminder of when they're on. But, even if you use a thermostat to control the oil cooler fan, it's still nice to know how much it's running and under what conditions. I can't hear either fan over engine and wind noise, so the lights help.
I was amazed to discover that the gauge shipped with light bulbs in all of the lights. All you have to do is connect one of the leads from a bulb socket to the hot side of whatever you want to monitor, then ground the other lead.
One caveat though. These bulb sockets are built to the same high standards as the rest of the gauge. If you try to remove a spade lug from a bulb socket terminal once it's been pushed on, there's a good chance the whole terminal will pull out, destroying the socket. My extensive field testing has shown this to be the case.
Serious types, like pilots, call these things 'annunciators', but a more appropriate term for people like me is 'idiot lights'.
