Tacho Havok

[ggn06awu]

Chaps,

Wiring a tacho in to the dash (http://www.vwheritage.com/vw_spares_Smiths-Tacho-T2-68-73-6000rpm-OE-Style-Grey-Face-AC957041_act_shop.product_pID_153077505.htm" onclick="window.open(this.href);return false, but after taking a piggy back off the 12v+ and ground from the Fuel / Speedo gauge, the fuel needle now goes nuts, spectacularly so when I then also plug the 12v switched feed from the light switch.

Is this an overwhelmed ground, or a feedback (diode might help?), or should I simply be running a completely unmolested 12v and ground from elsewhere?

Thanks in advance!!

 

[Zcat7]

I ran a separate 12v piggy-backed from a switched live at the fuse box and picked up a clean earth from the body. It seems to be the logical thing to do especially with what you're experiencing.

 

[kreemoweet]

The "G" terminal at the fuel gauge is not a ground, in spite of the brown wire color. It connects only to the
variable resistance in the fuel tank sender. The only ground connection at the cluster is the two-tabbed (or 3?)
dealio spot-welded to the metal backplate at the bottom.

 

[ggn06awu]

Thanks both!

Kreemoweet, I'll fish that other ground out tonight, it would certainly 100% justify the behaviour it's giving.