I have a Vettaid 8 gauge cluster. I recently rewired the entire car and relocated the battery to the right rear. I have a ground cable from the battery to the frame and engine to frame. I have grounds running through a distribution block directly to the battery for shift light, MSD 6AL, and gauges.

Here is the problem:

The tach does not work. I am getting signal to the tach for sure, the shift light works and is on the same wire. Also, as engine speed increases, the fuel gauge goes up. It starts at about 1/2 tank and increases with engineia rpm. Everything is wired correctly. I've tripled checked that.

Any ideas? More grounds?

I've also noticed the shift light flashes intermittently every once and a
while. Do I need a filter for the tach wire possibly?

 

If you haven't already, run a heavy duty ground cable from the battery directly to the engine....just like a stock setup.
Connect a set of heavy duty jumper cables from the battery (-) directly to the engine block as a "test" to see if you can get the tach to register.

 

Pics of dash please.

No help but allows you to picture *****.

GL in finding the issue

 

The switch panel, shift light, and where the power/ground distribution boxes have sheet metal covers that are going to be laminated with carbon fiber.

 

I haven't had time to do the long ground wire yet. Any other suggestions?

 

I relocated my battery to the right rear next to the bumper. I have a ground going from the negative battery to the chassis, and another 1 gauge cable going directly to the engine block. Do what engle suggested. Might cure your problems.

 

Finally got around to running another ground cable from the engine to the battery. I'm still having the same problem with the tach not moving and the fuel gauge going up as rpms increase. This one has me really frustrated. I know the MSD is sending signal since the shift light works.

Here is a pic of the power and ground blocks that run the gauges:

 

Run your gauges ground wire to the engine block and make it a larger wire than you show. Gauges ground circuit is affected by other circuit currents in the batt - wire to the block affecting the gauges. Recall that the original gauges grounds to the block for this same reason.

 

In all due respect your wiring is a problem. Your fuel gauge is telling you as is the shift light. The fuel gauge is a simple resistor voltage divider with a vaiable resistor in the tank and a fixed one in the gauge. It depends on good grounds at both ends to work correctly. The shift lights are all solid state if they can be programmed and have filter networks in them to get rid of stray electrical noise outside of the frequencies of interest generally anything above 1000 hz is out of the realm of possible. Bad grounds no filtering and the random flash assuming it is a quality piece to begin with.

The MSD large red and black need to go to the battery. The coil wires orange and black need to be twisted from the MSD to the coil and away from anything RF sensitive such as the ignition pickup or any sensor wires if an EFI car or data loggers if you have one. If you are not using the white wire for a points type pick-up cut is short and cover with heat shrink. The same goes for the mag pick-up wires if used twisted short and direct away from coil MSD and plug wires, if unused remove them as they will easily pick up RF.

Everyone has their favorite plug wires personally and good spiral core wire works fine and has 700 to 800 ohms per foot. The 40 or 60 ohm wire causes more problems than they fix.

 

I figured out the tach problem. Apparently vetteaid uses the ground for the lights (gauge lights) for the tach. I grounded this wire and changed the ground to the engine instead of the block and it works like a charm.

As far as the fuel gauge, it still moves with rpm. I was brainstorming and think that the underdrive crank and alternator pillows may be affecting it. What do you guys think? The sending unitbis ground to the proper location on the B pillar per the FSM.