I have a Fisher Pierce model 7790B Twist lock P/C that will flash the load on and off 3 times before staying on for good ! it does it switching LED or HID.It's rated for 105-305 volts and up to 1000w . Anyone ever seen this before ?

All cells must have some built in hysteresis, so that when it switches on the luminaire and gets a little additional light (reflected from the lamp), this won't be sufficient to switch it back off

In thermal cells the thermal device itself may be implemented as a sort of snap switch, this feature provides the hysteresis mechanically

In electronic cells there must be a sort of positive feedback circuitry (can be as simple as 1 extra resistor in the circuit). If this circuitry is broken, there won't be any hysteresis...

If the cell reacts like this only when the light level changes slowly into "dusk", but doesn't if the ligth level changes decisively (e.g. you cover the cell at once with an opaque coat to make it see darkness), this is likely the culprit

I have a Fisher Pierce model 7790B Twist lock P/C that will flash the load on and off 3 times before staying on for good ! it does it switching LED or HID.It's rated for 105-305 volts and up to 1000w . Anyone ever seen this before ?

Your photocontrol sounds defective to me. Whether it is an older Fisher Pierce 7790B, or a Fisher Pierce/Sun-Tech 7790B, it should not be flashing the load on an off. What date code is your 7790B?

Thanks guys ! This IS a Fisher Pierce Sun tech , the date is 6/20/12 . The reason I asked is this P/C came with a new in box with a never used fixture . Must be a factory defect !

 @ Ash  : It only flashes the load at dusk . If you cover the cell , the it just turns on normally.

Thanks guys ! This IS a Fisher Pierce Sun tech , the date is 6/20/12 . The reason I asked is this P/C came with a new in box with a never used fixture . Must be a factory defect !

 @ Ash  : It only flashes the load at dusk . If you cover the cell , the it just turns on normally.

Yeah sounds defective for sure.

Thanks guys ! This IS a Fisher Pierce Sun tech , the date is 6/20/12 . The reason I asked is this P/C came with a new in box with a never used fixture . Must be a factory defect !

 @ Ash  : It only flashes the load at dusk . If you cover the cell , the it just turns on normally.

It is indeed a defect, Ash just describes the plausible technical cause.
If you cover it, there is not that strong light feedback, so the remained hysteresis (the relay mechanical hysteresis and finite gain of the electronic) is enough to make it seem to work OK. But ion the real life the feedback uses to be stronger, so the hysteresis has to be larger to prevent cycling.
If you do not succeed to claim warranty fix, you may open it, take detailed enough photos so someone here may redraw the schematic (e.g. me... ;-) ), reverse engineer its function and maybe pinpoint the possible defective components...