LTx12s wiring back feed issue?
 

so.. wired ltx12s into 20b-fc.

computer 12v constant to fused 12v constant source, 12v acc wired to fused 12v acc source

fuel pump relay- 30 to fuel pump, 87 to fused 12v constant, 86 to 12v acc, 85 to computer

ignition coils= 6 msd coils, negative coil wires as per michrotech schematic, positive coil wires daisy chained to key on 12v source.

what i am experiencing

everything hooked up normally:
key on, green light, no fuel pump relay sounds. crank= no spark, no fuel, computer light goes out

test voltage drop at battery during cranking =10v = no computer light

jump computer constant 12v wire to a solid 12v source independent of vehicle:
key on, green light, no fuel pump relay- crank= no spark, no fuel, computer light still goes off

this is where it gets interesting

jump acc to 12v constant(no source of power from either wire, they are only jumped to each other) key on and to my surprise the computer light comes on and fuel pump relay is now on, hear fuel flowing through fuel rails,

turn key= crank, computer light on, fuel pump relay on, no spark.

unplug relay with this configuration and computer light goes off.

fuel pump relay unplugged
acc & 12 constant hooked to external 12v source- computer light on, no fuel pump(obviously)- crank= computer light on, no spark.

i am thinking i have back feed through the fuel pump relay into the computer but i am below amateur when it comes to wiring and i am praying to god that this is an easy fix and i have not damaged anything internally in the computer. also wondering about why i do not have spark at the coils but i would like to figure out the relay/computer power thing first. feel free to give advice on any of this though.

thanks for any help you can give

normally 30 is fused power in and the pins 87 and or 87a are outputs
( different styles of relay ,, be sure you only have relays marked 87 and wire them this way around )

with micro installs some problems can arise with a back feed issue when you make a self feeding loop for the relay and the system can remain turned on despite the key being withdrawn

the secret is in where you tie the pink wires and i avoid using their fuel pump pink
- using instead the existing fuel pump wiring and the ECU switched earth ( green wire ) to double blind swing the relay

if cranking and not getting the yellow blink then you don't have the CAS hooked up correctly

ok.
i will swap the 30 and 87 pins.

the wires that i am using is the red, the computer power pink and the green wire for fuel pump(going to relay).

i would use the stock fuel pump wiring but it is long gone.

as for the cas, can you possibly give me a quick run down of what i should be looking for and where the wires should be? i am using the stock 20b cas and was under the impression that it was already wired correctly since this is a used computer that was running well on a similar 20b.

thanks for all your help and any more you can provide.

So I swapped pins and success.. or so i thought.
First time key on with new config and computer goes on, fuel pump is humming.
Second time key on. Computer goes on, no fuel pump. Bypass fuel pump relay and pump goes on. Check relay fuse and its fine.

Getting frustrated. Getting worried I burned up the computer. This stuff scares me so much.

Someone please help.

got it handled. friend came by and had us up and running in under 30 mins.

everything works great.

thanks for your help bumpstart!

what was the problem and what was the fix?