[sigchuck]

Hi folks, I'm attempting to add a 930 tach with boost gauge (and all of its associated shortcomings) to my 911 chassis.

The tach is generally good and functioned fine for many thousands of naturally aspirated miles. During this time with no wire on the boost terminal, the boost gauge would peg with the ignition on/car running. I think this would generally indicate the tach is functioning as intended.

I have a Koklen intercooler on the engine with a factory 930 sending unit. Since my car is a 911SC, I ran a single wire from the engine compartment to the front trunk and connected the ends to the appropriate terminals (single spade on sensor and boost location on gauge).

I'm unfortunately still getting the same behavior from the gauge - it pegs with the key on/car running.

I've read that it can be difficult to get sufficient ground for the sensor via an aftermarket IC. I think the sending unit has a separate (and currently unused) ground post that I could run an external ground to.

My understanding of automotive electronics is somewhat limited, so before I take the IC back off, I wanted to see if you guys might be able to confirm the following:

1. Un-grounded, the factory boost gauge should be fully pegged with the car on or running.

2. A single wire from the boost terminal on the tach to the single spade on the sender should be all that's needed to carry the signal, assuming the sender is otherwise correctly grounded.

Thanks for your help! Happy to post any additional information that might be needed!