Hope it all works out with the new ECM. The 6 volts is an indication of a bad ground(ed) conductor or lack there of usually and the meter will give you a semi reading through the leads, which is why DMM aren't for higher voltages, if you have a loose connection they can still pick up a completed circuit, unlike a set of wiggys where it throws a load on the circuit and creates or shows a fluctuating open but DMM are great for low voltage. At first I was thinking maybe you had a loose terminal connection within the relay housing and the DMM was reading good but when a load was applied you would loose continuity but you have seem to made it clear that you've isolated it.