88 PU, its an aftermarket tac, but this just started happening after the fuse blew for the running lights and dash lights. So when the lights are off the tac works, but when i turn the lights on, it doesn't illuminate and stops working.

 

something internally in the tach? Only thing that makes sense to me.

 

Check your wiring, most after market gauges are wired to have a positive wire for the light and the bulb is grounded to the case of the gauge (i.e. tied to the vehicle ground). The dash lights are wired with a floating ground which goes through the dimmer (rheostat) to let the dash light intensity be adjusted. If you tie a hard grounded device into the dash lights (with a floating ground), things like that can happen. Best bet it to tie the tach into a separate circuit (that switches on and off with the ignition) and if you want the back light to turn on and off with the lights, hook it to something like the parking lights, not to the dash lights. It won't dim, but you can add an in-line resistor if the light is too bright.

 

parking lights??? i don't know if i have a circuit for that, as its a manual, unless i'm mistaken what you mean by parking lights. It said in the manual to have a good clean ground. So i just ran a separate ground straight to the battery. Everything else is wired in with the head unit. On that, it has an illumination, positive, negative, and signal leads.

 

ok to turn on your headlights you twist the lever so it clicks twice, right? turn it once. when your brakelights and marker lights are on. thats what hes meaning. wire it into those lights.

 

Fixed it for you.

 

Parking lights pr running lights is what I think you called them. The orange ones up front and the red ones in back that come on before the head lights.

What is the head unit "illumination" circuit hooked to?

 

Yes, so i am thinking it might just be the tac. I haven't jumped very far into the wiring, but my head unit it wired into the illumination lead that comes from the trucks wiring harness for the radio. On that, i noticed while driving today that it was stuck at 2,000 RPMs, so thats why i am guessing its the tac??? but i just check and it went back to rest. I don't know, but its weird that the tac is reliant at all on the illumination lead, i shouldn't even have to have it hooked it, all it should need is a signal, power and ground. hmmm... i wonder if i'm not getting a clean 12v, i guess i'm going to have to invest in a volt meter.

 

Tach may have a backlight but should work without that hooked up (just hard to read it at night). Volt meters are inexpensive (under $5):
- http://www.harborfreight.com/cpi/cta...emnumber=92020

 

Right, well, haven't gotten a volt meter yet, but i observed something weird. When the lights are turned off the tac is illuminated ????? thats confusing to me. So, what i am confused about right now is, why it worked fine before the fuse blew, but now the illumination is backwards??

 

Turns out, it was a bad ground, the connection was loose, on a side note there should be a "solved" button for threads.