TDI 2003 GOLF ASZ PD130. 157k miles.
Car owned for 4 years with usual tale of Golf faults and had to changed clutch in December after a failed slave cylinder.

Had a problem starting after a short journey but started on third third try but traction control light stayed illuminated though the car took me home a few miles no problem.
After restarting a few times without a problem at home the TC light went off.

Pulled these two codes, 01314 pointing to loss of power to ECU and 00526 brake light switch both intermittent..
Brake lights check out ok and working and have changed over under dash relay 109 that supplies the power to ECU.

After a change of relay I expected to start right up but for the second time did exactly the same and went third or fourth try and have since tried numerous times with it starting instantly on the button each time.
I suspect another problem other than the relay. Wiring,earths , ignition switch etc are on the list to check next

Can anyone point me towards the most likely or most common cause other than relay 109?
I read this is a pretty common occurrence and maybe somebody can pass on their experience that may save me a long hunt.
Intermittent problems are the worst!

UPDATE Went for a short drive today after numerous tests to see if engine would fire up which it did without problem and clearing the codes but knew the problem would still be there.
On return I parked up and tried restarting and it took four attempts with further codes logged including engine speed sensor 16705 and the dreaded 01314. In process of cleaning all grounding points in the engine bay . Have removed plastic scuttle cover - what bloody game that was! to access ECU - Removed both multi plugs looking for water damage but nothing apparent and dry with no green oxidization. Next step will be to check resistance in plug switched live, between ecu relay and also grounds to ECU.
I would like to think I can find the problem but see myself running out of targets to check. If I do find a n issue I will share the info as it could save some a great deal of time.

Thanks in advance. PF