HELP 4agte STARTER MOTOR PROBLEM!!!

[jamo4agte]

If anyone out there could lead me in the right path, or have ever had a similar problem to mine, the help would be much appreciated as I'm not that good with electrics.
-the problem is when I turn the key to on everything works fine, but when I go to turn it over nothing happens.
so I thought the starter must have been f**ked, so I began to take off my manifold and turbo setup.
i had a full battery and was reading 12.5 volts at the battery, and also 12.5 at the starter, so no power was lost, from its way from the boot to the starter.
I then took out the starter and connected it up to a battery outside of the car, and it worked fine.
I then put the starter back into the flywheel and directly hooked the battery up to the starter, and it still worked perfectly, and turned the engine over for the first time.
so I'm now not sure as I put the battery back in the boot, tested again to see it still had power, which It did, but still didn't turn over?
now I'm confused and not sure what it could be? I have an after market ecu that I've never had running, engine also has a fresh rebuild
if anyone knows what could be causing the problem please help me out
cheers in advance

[maxhag]

So you have 2 wires going to the starter yeah? The main larger gauge power cable (12v Battery) and then the smaller STA start signal wire (black/white)....

If you have a multimeter, if testing the smaller black/white wire, it should have 12V signal when the key is turned to the 'start' position...

Do you have a low mount turbo setup stopping you from getting to the starter? Usually, you dont need to remove the manifold and turbo etc to remove the starter motor... You should be able to do it all from underneath the car quite easily

[pizzaeater]

A starter motor on the bench has no load on it hence why testing it out of the car doesn't usually mean allot.