Don't have any way to test the tach wire.Thanks for the input,I'll get the parts ordered this week.should I just assemble the circuit on a bread board

 

Don't have any way to test the tach wire.Thanks for the input,I'll get the parts ordered this week.should I just assemble the circuit on a bread board

I would recommend using a breadboard first as might need additional components on the tach input.
Get at least 2 of the 100nf capacitors a 2N3904 transistor and some extra 5.1K resistors.

 

Revised schematic.

 

Not trying to be a pain in the butt ,but what type of capacitor should I buy. there's so many choices ....

 

C1 and C3 are film capacitors.
C2 is electrolytic.
All resistors 1/4 watt .

 

Hi All I am looking for some help with a project I've been working on. I have a adjustable shift light in my truck I would like to remove the 3v led and replace it with a 12v relay to control another circuit. I assume I need a transistor circuit but I don't have a clue what I need for parts.Any help or if someone could point me in a direction would be appreciated. Thanks Rod

Why don’t you consider optocoupler?

 

Why would that make any difference?

 

The shift light no longer works so Iam going to build something better suited for my needs

 

Does this look right?

 

Looks correct.

 

back again, does this look right

 

Almost.
See the revised schematic in post #43. Connections and components have changed on pin1.
The 1K resistor R6 should connect from pin6 to the anode of the LED. You show one side connected to pin5.
Don't use those long jumpers for connecting the grounds.

 

Wha/ would you use for grounds.

 

Just use the bare wires to connect the commons as short as possible

 

I hoped it up to power and the led is on

 

I hooked it up to power and the led is on?

 

I hooked it up to power and the led is on?

Wiring doesn't look correct and that's not the correct circuit.
I don't see the cathode of the LED connected to pin5
Use the circuit in post #43.
All the common ground connections including pin8 connect to the negative of the power supply.

 

Am I any closer lol

 

Not there yet.
The resistor on pin1 to ground should be 5.1K not 1K.
Next, the 1K resistor up top is completely wrong along with the wires from the LED.
The left end of the 1K resistor goes to pin6 not pin5, just need to move it to the left one space and the right end needs to move to the right one space along with the red wire from the LED.

 

I think this is right.but the led is always on.