TR6 Wiring problem

As part of our TR6 resto we were working to complete the wiring harness install. As soon as we touched the cable to the negative terminal we experienced a spark which suggested that somewhere we have a short circuit. So we methodically began to unplug to isolate the issue. We found that the brown wire connected the starter relay at C2 to the fuse box was the culprit. There was no spark at the negative terminal with that wire disconnected. My question is, what is disconnecting that wire telling me about where this short may be occurring. We can read the wiring diagram with an amateur's eye but need some direction where we might look to solve our issue. Thanks in advance for your input.

It would help to know what year TR6; you might want to add that info to your signature. I'm assuming this is a 74 or 75.

My guess is that you have the wrong starter relay, or else it is defective. Disconnect all of the wires from it, then use an ohmmeter or continuity tester (aka powered test light) to look for continuity between C2 and any other terminal. There should be no continuity without power applied across W1 and W2.

PS, if I'm correct, C2 is being connected to C4 without power to the relay coil, meaning the ignition coil is getting power through the WY wire. That is probably the source of the spark you see, rather than a direct short to ground.

Well, we finally got around to testing the relay and found no problems there. But, we traced the brown wire back to the fuse box and then focused our attention on the purple wire circuit on the other side and 'bingo', a dead short in the loom of a brand new wiring harness. There are two purple wires connected together at that terminal so we broke them apart and found that the smaller wire that served the seat belt warning system and warning light was the culprit. Our next project is to see if the warning light socket is faulty or the main plug to the seat belts is haywire. We were not happy that a new part is faulty right out of the box but if we can't find the short at the plug or socket we may forgo that part of the circuit. You were correct with your guess that it is a '74 TR6.

Defective new parts is unfortunately a very common theme these days.