I just finished replacing my engine with one from a donor car of the same year. Everything went very smooth. all connectors connected perfectly. Now for the problem...
I installed the battery to crank it, put the key in and noticed the interior electrical was freaking out, the engine tried to start but failed. then the switch would not activate the starter unless I turned it a few times. The a/c blower was at full blast with no control of the a/c system. The horn would intermittently blow and the gauge lights were off.


I didn't mess with the interior electrical other than disconnecting the battery and the relay/fuse box in the engine compartment.


Could this be a bad ground somewhere? I know of the two grounds at the engine mounts...is there any others I might check?


Any suggestions?


I checked the spark plugs for spark and no spark. The horn blows after I try starting it and pull the key out and wait 2-3min.

 

I found the culprit! below is the link to the picture. The donor engine was missing the bracket to mount this on for grounding. I didn't think anything of it and left it hanging. The problem was that it didn't have a good solid connection to the manifold and was arcing when the key was in the ignition. I took the bracket from the old engine and now it works perfectly!
Mazda Forum - Mazda Enthusiast Forums - taokarate's Album: 2002 Millenia Engine gounding issue

 

Now that I have the car running, how long do I wait for the computer to catch up with this new-used engine. Reason I ask is: the idle seems to be really high (1000-1100rpms) and as I come to a stop the high idle makes the car lunge a little if I release a little brake pressure. I did keep all the sensors, the throttle body, distributor, plug wires, etc. just incase I needed to swap something. Also, the CEL is on but it came on the first time I cranked it so I assumed it was because the engine hadn't been cranked in a while and stumbled at first. I have driven it about 40 miles so far.

 

Unfortunately the cel won't go off until you read the code and/or disconnect battery.
Think you should be interested in the code, but at least: clean the throttle body, MAF sensor while disconnecting the battery. After doing those, re-connect battery and let idle for 5-10 mins before driving.
Surely 50 miles is enough.