I want to install an aftermarket tach. I need to identify the +12v wiring for the instrument cluster to splice into the tach backlight. I would like to have the capability to use the dimmer to control the tach backlight.

What color wire should I splice into coming off the switch in order to incorporate the dimmer function?

Thanks...

 

Assuming this is for the '73 in your profile, it will be blue with red stripe. You should be able to find a tap for it without having to cut anything. When I put gauges in my truck, I used the leftover dash light connection that went to the old AM radio.

 

When you say tap do you mean there is a wire capped off that I can run a connector to? I was thinking I would need to put one of those snap connectors on the wire.

This is for my '73.

 

Please don't use t-taps or scotch locks. While they do work, they can damage the wire, and it's already 35 years old. I would recommend removing the insulation off about a 1/2" of the wire, then take a probe or awl and poke through the strands. Twist your new wire and push it through the hole, wrap it around strands and solder it up. This will make a much stronger connection.

 

I'm having trouble remembering if this is the case for a 73-79 pickup. On full size sedans of the era, for example, there were a lot of factory options that connected to the instrumentation lighting - for example, illuminated ash tray, backlit clock, etc. So there were a lot of dash light connectors behind the dash. If you needed to source from the dash lights and you didn't want to cut up your wiring, you could just use a matching connector to connect to the circuit instead. I'm trying to remember, and I can't think of any options for those pickups that would leave a spare dash lights connector back there. Like I said, when I put my gauges in, I used the dash lights terminal from the radio connector since my AM radio is long gone. I slipped a spade terminal in there to avoid cutting any of the original wiring.

I agree with ReAX; avoid the clamp-style connectors. The whole reason I brought up trying to find a different place to tap into was because you should avoid splicing at the headlight switch. If the connection wears out, you'll take out your entire dash lighting. If you absolutely have to splice, do it as far downstream as possible, such as the heater controls illumination. Either way, blue wire with red stripe is what you want. We're just trying to help you do it as clean as possible.

 

From what I have seen so far the blue/red stripe wire is easy to locate. As for finding an unused connector I will have to do a little more hunting around. Would this unused connector also be blue/red stripe?

 

If there is one, it will be blue with red stripe as well. Like I said, I'm not completely sure there is one on these trucks, but it won't hurt to try looking.