i need another line for my greddy gauge..im not sure what it is for but my guess this boost gauge is electric??? i dunno..i need this extra connector . i have one already..there are two inputs..the pic should help

 

Your pictures suck.
Im guessing its electrical sensor?

 

Here's the complete documentation for your gauge: http://www.greddy.com/img/PHP/products/pdf/702.pdf

You need two harnii. One connects to the car, carrying +12, switched +12, GND, and backlight. The other has a MAP sensor attached to it, and is what gives the actual indication.

(Ah, behold the power of Google.)

Presuming that you don't have said MAP sensor, junk the gauge and replace it with one of these:

 

i posted this thread about getting a pressure sensor harness for my greddy boost gauge and it is just about to drive me nuts...which part do i need ??? part # 16400062 or # 16401406??? i have searched the web..dude at greddy jus does not know??? his *** from the hole in the ground..i even sent him a pic..its not a gr8 pic but good enough..it is an electrical gauge..

 

Spend the $25 on a sunpro mechanical gauge from an auto parts store, they're plenty good.

 

You need the sensor. Right now you just have a gauge and the harness to power it up. The sensor will have it's own wire harness and a pressure sensor to detect vacuum/boost.

 

Mine reads 1psi disconnected

 

I just got a Stewart-Warner 114538 15psi guage from: Teamxxxracing.com

The SW guages are hard to find and he sent it to Canada for cheap. I only wanted a 15psi guage as I plan to limit to 10-psi and wanted more "sweep" Imagine trying to look at a 60psi guage trying to determine 8psi from 11 while your flying down the road.

I was going to buy a boost only guage but didnt. As a newb do I really need vacuum displayed as well? Help me understand?

 

The thing is what you think is boost is just relative pressure greater than atmospheric, commonly called gauge pressure.

The vacuum side is still showing positive pressure (there's no such thing as negative...just complete vacuum), it's just less than ambient. I've never really looked for a gauge that starts at "0", but I'd imagine the normal engine vacuum you're running 98% of the time would be tugging the armature inside against a stop, which CAN'T help calibration.

Having vacuum on your gauge is nice as it's all relative, and you can see when you're getting close to boost etc. I also check my vacuum at idle as it gives you an idea of how well the motor is running (should pull lots of vacuum).

 

Thanks,

What is the standard idle vac for a 1.8? Or is it too variable for each setup ?

 

My MS is seeing ~28 kPa at idle, or ~72 kPa below ambient. The conversion is .295 so that would be ~21" on a vac gauge. That's assuming my math is correct. It will be another month or two before I'm turboed so I haven't installed my boost/vac gauge yet.

 

Cool - thanks, i'm in the same situation, going to be intalling in a month or 2. It's my DD so I need to work out a backup and the courage to start a 2 week install journey into the world of FI.