Thanks for the reply!
Here is a complete detail of my hardware:
:::Programmer:::
Arduino Uno running ArduinoISP, Arduino 1.8.4.
10 µF cap from reset to ground
:::Target:::
Atmega 1281
Power:
Various switching regulators to regulate power to 5V at AVR device: I had probed to confirm it's not dropping below 4.9.
Clock:
16 MHz, with 12 pF caps on both XTAL pins.
:::Connections:::
Uno Mega1281
SCK (13) SCK (11)[PB1]
MISO (12) MISO (13)[PB3]
MOSI (11) MOSI (12)[PB2]
5V Vin Regulates to 5V at Mega
GND GND
RESET 10uF to GND
P.S As I'm writing this I've read CrossRoad's post...
If I understand correctly connections should be...
Uno Mega1281
SCK (13) SCK (11)[PB1]
MISO (12) TX (3)[PE1]
MOSI (11) RX (12)[PE0]
5V Vin Regulates to 5V at Mega
GND GND
RESET 10uF to GND
I'll check it in the morning.
P.P.S
I've been reading your post for about half a decade, just wanted to say thanks!