Hazard light electrical issue

Hi all, need a little help with an electrical issue, ie Hazard lights
I've fitted drl switch back lights to both front & rear turn signal lights, when I put Hazard switch to on both front lights illuminate(bright light) rears don't, now this is with Ignition off engine not running! (Battery volts showing 12volts. Start engine volts now 14, both front and rear indicators illuminated, but rears are quite dim, I've checked voltage to rear indicator lights at rear main plug & with ignition OFF, im getting max voltage of 7 volts, with engine Running, I'm getting max Voltage of 9 Volts.
Any insight to what would cause this issue will be very much appreciated (MOT Booked on Friday)
Also I've just Replaced the Lucas flasher relay with new 1.
After checking wiring diagram for indicator/Hazard light circuits, I see that this runs through the bcu could this be at fault for votage drop @ rear light unit connection plug(loom side)?

The indicator lights themselves are switched by relays which are controlled via the BCU, that is the relay coils are energised by the BCU which interprets what indicator to turn on and flash which is conditioned by the indicator direction switch or the hazard light switch. Tapping into the switched circuits (the circuits that the relays switch) should not really cause a problem. I do find your explanation on the wiring mod a bit vague and I am wondering why you are using the indicators for DRL functions.
Normally DRL's are either mounted separately either inside the headlight units such as COB Halo rings, or somewhere in the front spoiler as addition luminaires. Some people have also converted the front fog lights which are not an MOT mandatory into DRL's too. In most cases these are usually controlled by a dedicated controller sourced cheaply from auction sites etc, which switch the lights on when the engine runs and dims them at night. Some of these controllers have a secondary function which allow the DRL's to flash if an extra wire is added from the indicator circuits - they must flash amber not white if this is the case. If this is what you are trying to achieve then I suggest tapping into the wires from the direction indicator switch on the steering column and wiring each side through an isolating relay to separate each side of the indicator function on the DRL. You must be able to dim them when the lights are turned on at night and if fitted inside the headlight I suggest they turn off when the indicator is operating, and that means proper off - not flashing off when the indicator is flashing on.
I fitted HALO DRL's to the headlights of my previous TF and the MOT man did not like the flashing HALO rings when I wired them up. I had to take out the flashing function and do what I described above and separate each one with a isolation relay to turn off the HALO for the side which the indicator was flashing. I did a how to on here a few years ago describing the initial fitting of the HALOS.

Sundance