ok so just to clarify things a little.

the car cranks, so the start wire and starter motor are ok

the ECU gets power with the key on, and its ok with the engine running, but the ecu does not get power when the key is in "start"

so the place where the ECU is wired is important. is there a constant power AND a switched?

the other thing i've seen with the haltechs (although most other ecu's won't do this cause they aren't junk) is that the ecu shuts down when the voltage drops under 9ish volts. so if you had a haltech and a weak battery, it won't start because the ecu is off probably not it...

 

Next time you're with your car if you plug in the Buss fuse and the seatbelt light turns on try pulling the Meter fuse and see if this turns the light off or not. If it doesn't then try pulling the Room fuse.

 

************************************************** *************

Is it also true that this car/ECU worked in the past but not now????? And no changes have been made to the wiring of the ECU?

Like Satch mentioned way earlier....................in the START positon you disable the IG2 and ACC busses of the interior fuse box. So if this power source came from IG2 it would be normal for you to lose this source of power when in START. BUT the car worked in the past but now now for unknown reasons.

 

this is the puzzling part- there were no changes. No issues ever.
I drove the car that morning and got stuck in a parking lot, jumped the starter and drove it home.
Everything seems to be working, blower, clock, radio, gauges, etc.
The ECu gets a constant heavier gauge direct power feed, then a single turn on lead. Where it is connected we cant remember, we did it about 4 years ago. Not sure if we just probed around and found a turn on lead or put it to actual ignition source, but its a low voltage turn on lead not a power lead. It has the diagnostic light which comes on when keyed , changes for cranking, and then for running.

The dim seat belt light I was wondering if its the body computer? Maybe a loose solder joint? Maybe whatever the ECU is connected to is also to something on this board, will see when I move the car again.

 

drove the car twice, the dim seat belt light seemed to be off.
Leaving the car over a couple of days the battery stayed nice and strong.

in the middle of changing intake manifolds and what not, have to get into this wiring thing again.

Its weird because nothing was changed, drove the car somewhere and it wouldnt start when I wanted to leave. Have to trace where the ECU is getting its power from, but the odd thing is that everything else in the car seems to be normal.

Going to probe the wires, if its hot going in and the ECU loses then I guess I will have to send it out for repair. Will rig a push button start for the summer and do that over the winter.
Unless someone has some other slightly obvious thing to look for?

 

Not sure what this means but the ECU is powered by the Black/White wire from the Main Relay. Pin 1B for an S5 and pin 3I for the S4.

 

looking at the wiring diagram for the wolf we have 2 relays in the trunk, one for the fuel pump and the other for the power to the ECU which has a 4 gauge wire to power and a switched source , going to start there.

 

good advice to someone would be to make their own diagrams as they build their car, have pictures as well, keep this on a disk or usb drive somewhere.
5-6 years later you tend to forget small details of a build, especially when you get old, lol

Sometimes I forget things mid-thought

 

Was that the issue? The relay in the trunk?

 

Dont know yet, wont have it checked until tomorrow

It makes little sense because the computer is powering on with switched power like it should, it just cuts out while cranking