Sportline wiring

Have checked circuit from rear of fusebox -blue plug teminalA15  by disconnecting battery and connecting  power to spare brown/blue  spade terminal. Light lit up  and off with handbrake  switch. Reconnected battery as normal but no power from A15 with ignition on or off. Any help appreciated.

hand brake light is a ground at the had brake that goes back to the cluster as ground source for the lamp.  There is only 12V on the lamp and the lamp shoudl have 12V on one side, with the key in and turned to the run.

Make sure that your e-brake switch is clean and grounded to the frame.

it is a normally open switch when the lever is down.

Have double checked circuit  after disconnecting terminal from A14 and adding external power.brake light is fine so why no power from plug A15 with ignition on and engine running.

the wire is the jumper from a15 to C12, then out to your master cylinder to warn you that your pressure is low.

So with the issues you have had on the fuse panel I would suspect that you have internal corrosion on it or it has fried…

Both the parking brake and ebrake is a ground from a14 and picks up power on the gray/green wire off the back of the warning lamp after it passes through the lamp, it isn't power as power comes in to the lamp via the ignition switch the rest are grounds for the circuit.

I don't have a 84 diagram and basing it off the 85, as 84 was a mid year change, and you have to use both the 84 and the 85 diagrams.  84 was a 10 gallon petrol tank, where as 84.5 was a 13 gallon tank.  the spare tire size being full sized on the 10 gallon was 84, and the spare tire size on the 84.5 was a space saver spare, and a 13 gallon tank.

As far as I can see, the wire on the fuse in question isn't a power line it is a ground line from the Brake pressure sensor that is ground from the frame through the switch in the fuse panel, back to the warning input for the E-Brake  which is being fed voltage or 12V from the ignition switch.  The Seat belt warning relay is also a small part of that circuit, but the issue that I see is that you are mistaking that a15 should have power when from what I see it is a ground connection tieing the e-brake, and the brake pressure switch together at the lamp so the Brake light can also tell you that the pressure is dropping on the brake system as well as telling you you left the e-brake up.

The power from the ignition switch to the solid state device /lamp is on the red/black wire in to the lamp body.  So you may have a bad seat belt warning lamp as there is also a resistor in the circuit to power the solid state device.