The other day I was requested to install an aftermarket tach to my father in laws ’61 Chevy with a 235 Inline 6. The issue for me was that this tach had been purchased from a swap meet a while ago, with no instructions or information.
Now, I am from the Google generation. If I don’t have instructions, I’ll just Google the numbers on the part for more information. However, when Googled, the number 997SW6V came up with nothing worth noting. I knew it was a Stewart Warner, however that was about it.
After a short conversation with a tach ‘expert’ named Chris, I had the instructions I needed to set this tach up.
The first bit of confusion for me is that the tach was set up with a red, green, black and another red (light) wire. I could easily see the second red wire was for the light installation, but didn’t know what part of the harness to tap into for the rest of the wires.
An internet search told me to wire the red (ignition) wire to the battery. WRONG! This red wire needed to be installed to the ignition switch to the ‘key on’ position. NOT directly to the battery!
The black wire, according to this article was to be rerouted to the negative of the battery. This is not necessary, the black wire is simply a ground. Because the body is grounded to the engine, a bare metal bolt going through the firewall should be sufficient. I used one, with an appropriately sized eyelet on the wire, and added a nut to the back side.
The green wire attached to the tach side of the square coil that was installed with the mini HEI from Langdon’s Stovebolt. This is the wire that actually sends the RPM information to the tach.
So, red= power, black= ground and green= engine data.
The point here is not that you shouldn’t research this type of application through the internet, but you certainly shouldn’t take the first article you see as fact. You may be looking at a different product, or a different application. Or someone who is actually installing said product incorrectly. So, do your research, check multiple sources, and if still in doubt, contact an ‘expert’.