Voltage limiter.. Since both of those gauges work off of 5volts. The voltage limiter is found on the back of the cluster. I'm not familiar with 64 chryslers but almost all dodges/chrysler and plymouth cars back in the day used them.Awesome! Love this group very helpful I can't wait to get more hands on with this car after this I'd like to work on my guages I've been doing my homework, it's my fuel and temp guages don't work, I've read that are tied in together once fuel goes put temp guage also goes out any idea or know where I can start check.. I want to test the guages I just need to learn to take dash off and also how to test it, seen couple yt videos on it but with different model cars.