Reply With QuoteIn writing this I am assuming that the switch is switching power and not the ground connection. If not then it should be easy enoough for you to work out what is happening.Originally Posted by VladTepes
pin 30 is where your current gauge is connected to
pin 87a is the normally open (no power to solenoid in the relay) connection and this goes to the sender in your normal tank
pin 87 is the closed pin (power to solenoid) and the connection on here is currently going to your aux tank sender.
connecting the wire off pin 30 and the one off 87a just re establishes the original connection of your tank to your gauge.
you will need to connect the wire on pin 87 to your new gauge.
the switch has probably got power to the centre pin.
This power is not connected to anything when the switch is in the centre position. Your gauge is now connected to your normal tank sender (by connecting the wires on 30 and 87a together you just achieve this state permanently (as far as guage, sender and relay are concerned)
When you rock the switch to the G position the top pin (most likely) on the switch gets connected to the centre pin on the switch which then provides power at the top pin and that via the wire goes to either pin 85 or 86 of the relay to energize the solenoid and pull the relay into the closed position (pin 30 gets connected to pin 87) (if 86 is connected to your switch then 85 will be connected to ground if not it is vise versa).
When you rock the switch to the fuel bowser position you are just connecting the power at the centre pin on the switch to the bottom pin (most likely) and the wire on the bottom pin is going to your transfer/fuel pump.
Take the wire you have removed from pin 87 and route that to your new fuel gauge.
You can either use the switch you currently have to control your pump or replace it with an on/off switch.
I think that should clear up why you have to connect so many wires together etc as explained by langy.
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