installing a tachometer

i have everything connected except for the positive power. i need a wire that has current only when the key is in the “on” position. dont see why it cant be on with accessories but yea. its what the manual says. whats an easy wire i can find for that? i have a 98 s10 if it helps. and jeez feeding wires through the firewall is annoying. :rolleyes:

usually the fuse box on on the inside of the cab. If you have a voltmeter, or even a 12V light on a jumper wire, probe the fuse box with the key off, to see which fuses are dead. A tach will draw almost nothing, so you should be able to jumper it into any fuse that is only live when the key is on.

On most cars, the radio power is an obvious choice for what you are doing.

Do you have a manual for the car? It should have wiring diagram in the back.

What about the power supply to the rest of the instrument cluster? That wire should be pretty easy to find.

like a haynes manual or a manual that comes with the car? i have the chevymade manual yea. ill check it tomorrow. and well do you think the radio power would be fine? i had assumed it would be until i read the installation manual and it said it has to be a wire when the car is “on” only. not anytime else. dunno why. the fuse box way would be the easiest. i guess i can do that.

Is your radio on when the key is off? for most cars, its not.

The reason they want it on the accesories line is so it will not drain your battery (dead) when you are not driving the car.

Even the little light in your glove compartment will drain your car battery completely if it gets left on long enough - if you park the car for several days (dont ask! :^)

well yes and no. the radio stays on even if i pull the key out until i open the door.
actually i think i got it. plugged around with a voltmeter in the fuse box and found a fuse labeled “gauges” is only live when the key is “on”. thanks to whoever said that. except i was working on the car in the dark garage with the domelight on as my worklight… guess what. it drained my battery lol. so i had to waste valuable time jumping it. which is why im still awake. just finished some hw a few min ago. well thanks. i think i got it working. now will it work for a long time? lol. need to go find a torx driver tho. cant get my plastic steering column cover off… so its ziptied on now :rolleyes:

well the tach works now but now my fuel gauge wont turn on… and my digital odometer/gear indicator will only be on when i have the keys to “accesories” but not when its “on” i did wire the tach to the “gauge” fuse… is the tach taking all the current? anywhere else i should take the power from?

I don’t see why a tach needs to be always on.

It’s a gauge for tasting/measuring the condition of the vehicle when it is on.

Does it have an onboard computer or something??

I just don’t understand why something as simple as a tach needs to be always on. The only reason I can think of is if the actual working of the tach is digital and so it doesn’t lose it’s “memory” in the off state. I can’t see the reason for one of those compared to a mechanically driven one though.

Do you just want the dummy (shift) light so it looks cooler?? lol

i think you misunderstood something… or i wrote something weird… i dont want it always on… i just want the tach on when i have the engine on. and dummy shift light? since when did i have a shift light? i bought the cheapest tach i could find lol. i just need it for the winter to notice my tires slipping. (actually dead leaves are quite slippery too) i need to find a wire that is on when the engine is running but off when its dead. i tried the “gauge” fuse and it didnt work, as other things started to not turn on…

OOh… I read “on” (truck on & running) as “always on” (dome light, etc.) Sorry about that.

As for the answers to your question now, I have no clue.

if your gauges stopped working check the fuse - you may have shorted something and blew it out.

I’d try taking the power from the fuse going to the wipers. This would be a much heavier fuse than the dash gauges would have plus the wiper fuse will only be live when the ignition is at the “ON” and “ACC” positions.

Now for another suggestion that hasn’t been mentioned yet,

If you’re truck isn’t fully loaded with options you may have extra openings for fuses in the fuse block. If you use a meter you may find some open slots that only have power when the key is on. If this is the case then it’s OK to add a fuse there and tap off of it if need be. To keep costs down auto manufactures use the same main wiring harness whether or not a vehicle has certain options. The wires just don’t have anything to connect to (left unplugged at the accessory end) and the fuses are left out.

thanks everyone. i poked around a bit more and found a fuse opening thatll work. my truck would be the least loaded possible. and yea. the “cruise” fuse was out. i guess its not a cruise control fuse. the “cruise” musta meant fuel gauge/display thing… oh well. its working fine now. thanks! now for looking for a torx bit thatll take my steering column cover off… hmmm… oh does chevy use metric bolts now? or was the nut i had just the wrong thread?

I dont know for certain, but my 4 saturns are GM cars, and they are all metric