Here is the problem:

I have an autometer tach in my car that stops functioning completely when it gets dark and the headlights turn on.

Background:

The tach is wired with the lighting wire plugged in the back of one of the '5' fuses on the driver's side (this was recommended in another thread I had found). The tach functions perfectly during daylight, and quits at night (not only does it not light up but it doesn't even show the proper rpm's). Unplugging from the 5 fuse during the day causes the tach to not function at all.

Please help:

How can I get the tachometer to work during the day and night time hours, and also light up during the night so I can actually see where the rpm's are at?

Any help is greatly appreciated.

 

I can't imagine anyone suggesting you use the TAIL LPS fuse to connect a tach. I think what was meant is to connect your tach power wire to the slot marked IGN two rows below that fuse. The IGN slot is a single connector (no fuse in it) that provides ignition switch controlled power specifically for aftermarket accessories.

Also, it sounds like you have your tach ground wire connected to one of the lighting system power wires. Check that the wire you connected to the TAIL LPS fuse wasn't the ground wire by mistake. During the day the tach will work because it grounds there since the lights aren't in use. At night you end up with no ground for your tach because the wire has power on it when the lights on.

Now, you could use the TAIL LPS circuit to power the illumination of your tach if it has a separate illumination wire (some just light up all the time). However, a better way would be to connect the tach's illumination power wire to the dark green wire at the dash dimmer switch. That way the tach lighting will dim when you dim the dash.

Basically, you should check your wiring so that the power wire goes to the fuse box IGN slot and the ground goes to a solid chassis ground (there is a ground bolt under the dash behind the left kick panel - you'll find some black wires already attached there).

 

Here is where the 4 wires are currently spliced in:

The green wire goes to the PCM to get the tach signal.

The red power wire is spliced into a pink wire at the back of the ASR button.

The black ground wire is wrapped around a screw that holds in the headlights/dimmer panel but is in no way actually connected to the lighting system itself. Also, the screw goes into a metal plate against which the wire is hence lodged when the screw is tightened.

Finally, the white lighting wire is plugged in with the IP Dimmer fuse.

With these seetings the problem is as described in the first post.

Note: Prior to this setting I had the white illumination wire spliced in with the dark green dash lighting wire, however, for some reason the tach light only worked when the dash lights were turned all the way down, and didn't work at all otherwise.

Please help, I feel the ultimately the problem remains the illumination/white wire which I need to hook up somewhere else to get the tach to light up. Secondarily, the ground may not be very good, but I don't see this being the case since the tach works during the day. The other two wires are properly connected, without a doubt.

Please help!

 

I would try moving your ground wire. I don't think you're getting any ground at all where it is currently connected. The metal plate is merely reinforcment for the switch mounting in the plastic dash - it doesn't connect to the chassis anywhere. Try connecting to the ground bolt behind the kick panel or tap into the black wire at the radio.