engine dies when fans turned on

i tested the voltage with engine running and at the battery it was 12.45 and dropped to 12.1 as the fans came on and the engine died.

ok my stupidity , after reading the last 2 posts , i checked it and there was an extra wire lead coming from the fan relay that was hot when the fans were off so i was using it to power the msd. so it must be dropping out when i turn the fans on. i will find another power source for the msd that is coming right from the batt. one of these days ill get it wired right.