Multifunction tach gauge and 1991 115txrp

I just picked up a Yamaha multifunction tach gauge. Please see the link below for a picture of the gauge and wiring.
http://cgi.ebay.com/ebaymotors/ws/eB...MEWN:IT&ih=011

This weekend i will be installing a 1991 Yamaha 115 txrp , 2 stroke, w/ power trim. It's remanufactured, fresh paint and new 1998 lower unit. I'm stoked to get it on the boat. Anyway I picked up a new 703 side mount control unit which has the power trim switch on it. My question is will this gauge and all its functions work with this year motor? I thought i read somewhere that it wont work with pre 1994 motors. Does anyone have the installation instructions/wiring diagram for this tach that they could send me?

THanks for any help you can offer. Any pointers about installation are much appreciated as well.

[boats.net]

You will need the wiring harness.
68F-82553-80-00 Trim/Oil harness
6Y5-83553-N0-00 Gauge harness
6R3-82541-00-00 Adapter harness
6N7-82541-00-00 Adapter harness

will i even be able to get rpm without all these additional harnesses? I thought the 703 controls came with all the harnesses i needed? Or is that only the case with a newer motor?

[boats.net]

The 6Y5-83553-N0-00 is the harness that connects to the green,yellow,black wire on 703 controls goes to console to connect gauges. With this connection the tach will work but the trim indicator, overheat light and oil level indicator wont work without the 68F harness and adapters.

What is the orange wire in the 4 prong connector coming out of the gauge. I think i figured out what the other three are, just not the orange.
black = ground
gray = tach signal
pink = sending unit to fuel gauge
orange = ??

I have 4 wires leaving the engine that match. What harness is it that i need to connect these to the engine?

[joehydro]

Orange is 5V