I found a couple of small volt gauges from late '90's Jaguars XJ series in the boneyard this weekend. They are in sweet condition and will fit just under my small clock. I tested them both by touching the leads to the battery, but there was no movement of the needle. There is one black wire and one green wire along with a white/red wire coming off of the the backlight bulb. I can't imagine that both gauges would be inoperative. How do I test it further too see if there is an issue with them?

Thanks.
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'86 sedan with 465,000 miles on the original engine and automatic transmission