I've done the easiest swap known to man and somehow missed or overlooked something.
built d16y5 block stock d16y8 head
I have full power to both fuse boxes. Grounds look good. No cel or any other lights other than battery light with key on. engine turns over strong with key.
battery tests fine with 12.7v and adequate cca
Grounds are:
thermostat housing, cylinder head to chassis, transmission to chassis, battery negative to chassis AND transmission, all tight and clean.
I wired the aem wideband to the ecu following pherable write up via my jumper harness.
I removed the jumper and plugged the stock ecu in to no avail.
I've done harder swaps without issue but this little d to d swap has me stumped.
I have full functions with the key on like wipers lights etc
just no ecu and no relay clicking. no lights on dash other than battery. I have read other threads but can't seem to find this exact issue.
all testing done with a test light that has a voltmeter built in. I'm buying a multimeter after work.

Anyone have any idea? I have looked over everything 100 times lol must be missing something.


EDIT...1999 Civic coupe dx
P28 with hondata s300v2
Speed factory jumper harness OBD2b to OBD1

 

Have you tried applying power directly to the main relay to see if it closes? The CEL should come on and immediately turn off. Do you get power at the ECU fuse in the engine bay?

Years ago I had a weird issue where the car would crank, start and shut off as soon as the key sprung back into second accessory. Found the key cylinder was corroded.

Also had an issue with the o2 power wire shorting on the subframe once. Popped the ECU fuse immediately every single time.

 

I have not applied power to the relay yet. All fuses under hood and under dash looked good using the test light and I even pulled the ECU one to double check it visually.

 

Are you using the original '99 Civic DX engine harness ?

 

Factory dx harness with VTEC wired.
I took the hondata and jumper harness out and reinstalled the factory dx ECU and still nothing. No beeps no lights.

 

I tested the main relay with a multimeter and everything checks out there the relay clicks when power and ground are applied and has continuity in the correct places.
The plug for the main relay has power and ground signal but the relay doesn't click with the key.
Checked the grounds with the multimeter and everything checks out there. I checked the thermostat by touching chassis ground and then touching the wire connectors, not the bolt. Should I check from thermostat directly to relay??

Rechecked all fuses and did continuity testing on them for fun. Everything checks out.

 

A week ish into it and still no ideas. No power on main relay pin 5 with ignition on. Ignition functions everything else, testing continuity between pins tonight. Went over every ground again. All fuses showing good and secure. I have constant power to relay just no signal. Does anyone know if the wire at pin 5 is the same color that comes out of the fuse box under dash? I have two yellow with green wires at fuse box, one has switched power one does not. Could the fuse box be burnt internally?

 

Well I added newer ground cables to everything and I replaced some fuses that looked good but maybe were not(?) I now have full power and dash lights etc. Thanks to those who helped along the way!