Tach install help. Need 24v switched power

[NVRENUFF]

I need a little help installing a tach. I have a 24v diesel VDO tach out of a dozer that I'd like to hook up, but need 24v switched power. Is there any 24v switched supplies under the dash already? I wired it up temp to make sure it works, and it's dead on using the alt tap. I guess is worse comes to worse I could use a 12v relay for the 24v.

Also, does the brown/white wire go into the dash from the alt already?

Thanks ls for any help!

 

[NVRENUFF]

Nevermind, I can use 12v switched and just run the ground wire all the way back to the battery -N-. That'll give me the 24v I need. Should have done all this while my shop AC was on.

 

[richingalveston]

brown wire goes to the big diagnostic plug under dash if you still have it. not sure which pin but that is where it goes. probably need a relay. All power switched on by ignition is 12 volt that I know of. 24 only does glow plugs and starter.

I do not believe running the negative the way you describe will get you 24 volts.

 

[cpf240]

brown wire goes to the big diagnostic plug under dash if you still have it. not sure which pin but that is where it goes.

Don't forget it goes to the Tach Buffer module before going to the diagnostic plug, so may need to find it before the module, though I don't know what affect the module has on the signal.

probably need a relay. All power switched on by ignition is 12 volt that I know of. 24 only does glow plugs and starter. I do not believe running the negative the way you describe will get you 24 volts.

I agree with this. Use a relay that is switched by 12v, perhaps taping off the hot side of the voltmeter for the 24v, or a 24v source in the fuse box to power the gauge.

 

[MarcusOReallyus]

Use 12v switched to control a relay which controls 24v to the tach. Fuse things as needed. Easy peasy, completely safe.

Use a relay rated for 24v.

 

[blueblaze]

isnt the bottom 10amp fuse on the fuse block 24v? Don't know if its switched or constant but there is 24 at the fuseblock.

 

[drewzee87t]

voltmeter power supply is 24v switched. Just tap that.

 

[cpf240]

voltmeter power supply is 24v switched. Just tap that.

Nope, it is hot all the time. The "switch" for it is making the ground connection, not the hot.

 

[NVRENUFF]

I didn't even think about the volt meter, think I'll go check that out!!!

 

[drewzee87t]

My badnovsky. Thanks for that clarification