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I suspect your black lead comes from your furnace limit. What's thrown me off so far is your statement "I have a R7284B Honeywell controller that was working fine however there is no diagnostic display". If you had no line voltage feed besides the limit lead then you don't have an L7284. It's probably an older ignition control that didn't use a hot line in because it had no display. So what you need to do is run a hot feed directly from the 120 v line in for your furnace. How this works is the thermostat calls in the R7284 but the furnace only supplies power (to LIMIT) as long as the furnace plenum temp is under the furnace high limit setting. The new line in is what powers the display. The display is working now because your limit is closed and is hot.
There is no limit on the R7284 the limit is on your furnace. You don't have it wired right. I've stated several times what the correct way to wire this is. If you don't want to wire this properly there's nothing more I can do for you.