Hi all, I have just installed a haltech platinum plug play ECU and seems to be having issues with it turning on  after checking relays and fuses I can see that when the car is in the on position pin 3 on the eccs relay is showing 5v so I replaced the relay with a new one and still same issue, however when I remove the relay and jump the relay connection therefore giving it direct 12v at pin 3  the ecu turns on and it all works like normal.

Therefore if it's not the relay what could be causing the 5v at pin 3 instead of 12v

I am running  no MAF if that makes any difference and the car is a 1991

Any help will be much appreciated

 

Iirc and it’s been a while that board is prone to corrosion. So I’d make sure it’s all clean for starters. Then I’d look at how your taking that measurement, your voltage may be off if the ground isn’t a clean one, same as the rest of them. 
 

Did you just switch for another relay in the car or is it new? My relays were starting to fail and I had to go through and replace many of the higher useage ones like the ECCS and headlights. The previous owner of my car had extended the loom and fitted a Siemens relay. 

Oh also as I brushed my mind pinged back. Isn’t that relay fed by another relay. 
It’s the Accessory relay I believe. I may be mis remembering. 

For ECCS relay wiring reference: