Tilt/trim gauge wiring

Ever since getting my boat back with a new E tec on it, my tilt/trim gauge has not been working. They put in a new control box and wiring. Right now, it appears that there is a +12V, ground and -12V hooked up to the gauge. The +12 is hooked up to the terminal with an S marked next to it. The ground is to the G and the -12V is hooked up to the terminal with an l (looks like a small l). There are a lot of wires below the dash and what appears to be a similar set of 12V +,- amd G leads. My feeling is that it was not done correctly, but I do not want to make another trip to the dealer. I asked the dealer to send me a wiring diagram, but they did not. Any suggestions appreciated.

The +12volts should be hooked up to the I terminal, -12volts to the ground, the S terminal gets hooked up to the sending unit on the tilt-trim on the motor.

Thanks, I will double check my readings and try that. I am not sure if the 3rd wire they have hooked up is the sending wire though.

They had the positive and ground on the correct poles. Not sure if the other white wire which was part of a 3 wire set is the correct one or not. The gauge was working prior to the new motor installation. It would be nice if I could come up with a diagram for the new wiring harness put in the boat. There are more wires and plugs coming off of that which I have no idea what they are for.

Found a diagram on the Evinrude site, but it did not really answer any questions.