Fuse 46 doesn't blow but testing with the fuel pump 5P connector unplugged (and fuel pump fuse in) results in a fairly loud electrical scream from something under the back right under the steering column. Here is a pic of the unit in question (brownish connector):


I also took video:

 

Would seem to be the fuel pump main relay that is making all the noise:



Any further advise/suggestions would be very much appreciated.

 

Based on this thread, it would seem it is also known as the "PGM-FI main relay". Which the s2000 manual tells me is fused by fuse 46.
Guess it cannot hurt to track a replacement down and see if that fixes things?

 

That style "main relay" has been an issue in Hondas for years. Sometimes, turn the key on with it plugged in and give it a couple of firm taps, you may get it to power up and run. It powers both the PCM and the fuel pump.

I've done this to personal cars to get them home. The last car i had to do it to was a 98 Accord v6. Tapped it while key on, heard the pump prime, started it and drove home to get a new relay.

 

Yeah your main relay needs to be replaced, sounds like bad electrical connection from burnt out contact points.
This main relay is not designed to handle the added current aftermarket high flow fuel pumps needs.

 

I replaced it with one from Autozone that is supposedly comparable to the one I had (Mitsuba RZ-0159 as pictured earlier in this thread):
http://​​​​​​​https://www.autozone.c...ump/419956_0_0

That Mitsuba one I had is apparently Honda part 39400-S10-003 and is for a del sol, crv, civic, etc. Not for the s2000.. weird it was installed in my s2000 (and hasn't been a problem).

But Honda part 39400-S1F-003 is the one that is meant to go in the s2000 (I've ordered one from Honda, it'll be here Wednesday):
https://www.hondaautomotiveparts.com...in-39400s1f003

Anyway, with the Duralast one installed when I key-on (with the 15A Fuse 46 newly replaced and the fuel pump's 5P connector disconnected): I now blow Fuse 46.

 

The picture from the manual you are referring to is only a test for the fuel gauge, not sure if that has anything to do with your problems.
Pin 4 and 5 is for the fuel pump power.

 

OK, thanks for clarifying.

Where I currently stand is:
- disconnect all connectors from the ECU
- disconnect the immobilizer
- disconnect the fuel pump
- connect the fuel pump main relay (PGM-FI)
- turn ignition to ON
- fuse 46 blows every time

So there has to be a short to ground somewhere behind the Fuel pump main relay?

Because if I disconnect the fuel pump main relay and test its connector's 7 pins like documented in the s2000 service manual (pages 11-102 and 11-103) all tests successfully as documented (without blowing fuse 46). That is until step 11 and 12: which asks you to reconnect the PGM-FI and turn ignition on. As soon as I do that fuse 46 blows.

 

Fuse 46 doesn't blow if I pull the 15A fuel pump fuse (#2 in fusebox above the driver's kickpanel). Doing so stops the +12V from ever entering the fuel pump main relay. My problem must lie at or behind it.
Looking at the various wiring diagrams in the service manual it looks like the main relay's BLK/YEL wire is fused by fuse #2 (it is the WHT/GRN wire that provides +12V). So +12V is entering the main relay and doesn't blow fuse 46 (unless I have fuse 2 installed). Not yet seeing how fuse 2 relates to the wiring of the fuel pump... to be continued. (Wishing I took more EE courses in school _and_ had more coherent documentation, awkward fumbling all over the service manual to see how everything _really_ relates.. just bought the electrical service manual on eBay though)

 

Fuse #2 supplies power to the fuel pump, it also powers the coil that switches on power from fuse #46 to the ecu.
Here is the diagram we are both looking at (if anyone else is interested )
snitm: Did you replace the main relay with a new one or are you waiting for the correct part?
Have you tried to open up the fuse blowing main relay and have a look on the inside?