Simplex 4006 with 4050-80 problem

Ok so I recently got my hands on a 4050-80 light plate. The seller already put a diode or whatever you call them on the positive bulb wire so that it would clear a panel trouble, however, when I installed the device to my simplex 4006, properly with polarity correct, the trouble cleared, but when I put it in alarm, the panel automatically crashed and the nacs were going all wacky with the voltage. Now I know it’s not a panel problem since I disconnected the wires on the NAC terminals, set it off and the panel went into alarm just fine, so I’m guessing it’s something to do with that diode? Maybe I need a specific one or the 4006 doesn’t like them? Need some help with this one

That is really strange and I don’t have a ready explanation for the issue. The 4050-80 is a single lamp unit that typically uses a type 1829 lamp. Those are 28 volts at 0.07 amp bulbs. The diode Simplex supplied to add on a supervised circuit was a 1N4004 which is a standard 1 amp 400 volt unit. Nothing special on any of this. I connected many of the 4050-X lamp plates to 2001 systems over the years. My only wild guess is that somehow the lamp socket or the bulb itself is internally shorted. That would load down the power supply in the panel.

Also I should note that the 4051 horn and the 4050-80 are spliced and wired together on one NAC. Maybe the horn goes crazy when a diode is connected to it? Maybe they were designed to be on separate circuits

The 4051 is a DC horn so should have a diode in it already. Check to see if the 4051 has the suppression MOV across the horn coil. If it does not the problem could be back EMF from the coil. That would cause high voltage spikes get into the panel power supply.