Tach Wiring - Backlight Hookup

[Cubman]

I am wiring my cheap tachometer from O'Reillys in my '78 K10. I need to hook up the white wire to illuminate the tach when the lights are turned on. This wiring diagram says that I should tap into the brown wire from the headlight switch for it to come on with the parking lamps, and the light blue wire for it to come on with the headlights.
http://brochures.slosh.com/wiring/78 Chassis 2.pdf

I took these pictures a minute ago. Do I have the right wires picked out to tap into? Should I have the tach light up with the parking lights or headlights?

 

[dyeager535]

I can't see the photos here, but I would suggest that ANY time you do electrical work, that you confirm your suspicion with a voltmeter, even when you have a diagram.

It's either going to be ground or a 12V source when the headlight switch is turned on, real easy to verify with a meter.

 

[bmsmalley]

for a cheap test, use a test light with a pointed end. push it into the wire of choice and then turn on the lights and work the dimmer. the test light should respond accordly.

 

[dyeager535]

I'd recommend not pushing a probe through the wire. They get enough corrosion with the jacket intact, and while a small risk, it does introduce the possibility of a short that otherwise didn't exist.

As an alternative, find the connector, and push the probe into the back side of the connector on whatever wire you want to check. Most under-dash stuff is not protected with a seal so that technique works well.

 

[oatsk5]

I ran mine off the fuse box.

 

[Jason4x4]

should be hooked up to the dash lights, that way it dims with them.

 

[dhcomp]

Hook up to the illumination wire at the stereo. I think its orange.....

Thats where i tapped illumination wires for both my gauges

 

[Cubman]

I didn't know you could dim the dash lights? How do you do that? When I wired up my tape deck, there was a yellow wire (12V Bat), a grey wire that never had power, and a black ground. I had to run a 12V Ignition Hot wire because of the P.O.

 

[Jason4x4]

the knob you pull to turn the headlights on, tun it, all the way 1 way turns the dash lights off, all the way the other turns the dome light on.