When I turn on my sonar with engine off the digital volt meter changes constantly it varies (high to low reading by as much as .24 volts). Is this normal ? The rate of variation changes almost constantly.

This is a shot in the dark but I was wondering if it is a simple as a bad wire connection and the voltage variance is because of the lack of consistent contact in a butt splice?

I've seen that happen for two reasons:
- bad contact in a cheap, in-line glass carttridge fuse holder. Turn on your sonar, jiggle your fuse holder and see if the sonar shuts off. If so, that's your problem. Replace the fuse holder with a weatherproof fuse holder that uses the ATO-type blade fuses common in mondern cars.
- If you increase the backlight level in some sonars, the sonar voltage readout can change as much as 0.5 volts. My 334C does that.

Or, its normal. .24V is 2% of 12V. Digital voltmeters have a tendency to dither a bit, particularly inexpensive ones. your sonar is only providing the voltage reading as an accessory service, and they don't spend a lot of money on it. You sonar should function normally when the battery voltage is between 8-18VDC.