Run switch - 4 pin relay set up with 3 wires

Question

Are there any issues with powering pins 85 and 30 from the same 12v wire? The starter on my friend's 1981 Yamaha XS45 was not working, so I upgraded to a modern solenoid. I followed all the wired with a multimeter and figured out how to hook up the relay and got everything to work, but from the old set up I only had one wire with 12v power, so I hooked it up to pins 85 and 30. This means I had one wire left over from the old set up and for the life of me I can't figure out what it does. It's not 12v and it's not ground. I've all electrical components (e.g., turn signals, brake lights, etc.,) on the motorcycle and everything works.

P.S. I did the same thing with the headlamp - again left over with an extra wire.

Answer 1

As long as the one wire you have connected to 30 and 85 is sized to handle the load, and you have a switched ground, then there is no issue. As this diagram you linked to shows:

The relay is designed so you can have a very small wire connected to 86 that only carries enough current to activate the coil in the relay and a thicker wire to handle the load connected to 87. The small wire is the "switched" wire and the switch can be on the positive side or the ground side. If the positive was switched, a separate wire would come from the switch and connect to 86. Your application must be using a switch on the ground side. So, since the switch is on the ground, there's no need for a separate positive connection to 86.

Now, as to what the 4th wire was for? I don't know that. It could be a redundant positive wire meant for 86 that has been damaged, but that's just a guess.