Where do i hook the signal wire for a tachometer in my 98 s10

https://easyautodiagnostics.com/nissan/3.0L/ignition-system-wiring-diagram-1

You will need a wiring diagram but I suspect you can't install it without creating problems in the ignition system. If you can hook it up it will need to pick up its signal from the crankshaft position sensor output line.

What tach . factory in the instrument custer , Aftermarket ? The tach signal comes from terminal E at the ignition control module and the wiring diagram for a 1988 pontiac bonneville 3.8 L is a white wire .

Aftermarket or factory tachometer? ignition coil pins A,B,C . B is white wire -this is tachometer signal to instrument cluster .

connect tach wire to negative side of ignition coil and ground anywhere you find a good surface for the ground. there should be instructions that came with tach.

It is usually to the positive side of the coil - also depends on what type of distributor cap you have, if there is a 3-4 wire plug that goes to the cap, one of them should be marked TACH

Recheck your wire harness to your trailer hook up. You may have a short in the wire. Good luck 

Unplug the turn signal relay from the fuse box and start you engine. Does it still make that noise?
If yes... Put the relay back in, that is not the problem.
If No...Then the relay could be bad, replace it!

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IT'S A BLUE WIRE ON THE BACK OF THE CONNECTOR THAT WOULD NORMALLY GO TO THE FACTORY TACHOMETER IN THE DASH. YOU HAVE TO REMOVE THE DASH GAUGE CLUSTER TO GET AT THE CONNECTOR. THE CONNECTOR WILL NOT BE PLUGGED INTO ANYTHING IF YOU DON'T HAVE A FACTORY TACHOMETER (DX, CX, HX ETC...YOU WILL HAVE TO SPLICE INTO OR CUT THE BLUE WIRE FROM THE PLUG. IT GOES TO TACH SIGNAL WIRE ON YOUR NEW TACH.

Spark plug wire