Factory Tach question

[76K20]

Got a 76 K2o with a factory tach in dash.  Go power at the tach on the pink(hot) wire and got a good ground but can't get a reading on the brown wire coming from the distributor with a 12 volt test light.  Do I need to use a meter?  what setting if so?  Also there is a resistor in the brown wire how can I test this.   Thanks, Alan

[LTZ C20]

The wire from the distributor will only have power comming from it if the engine is running I believe. Not sure what to what setting a meter needs to be on.

Are you trying to diagnose a problem? Tach not working?

[76K20]

Tach is not working.  I tried it with the engine running.  I'd like to make an effort to get the factory tach working before going to an aftermarket.

[LTZ C20]

Ok. Look in the tech section, under your year, the service manual might have a section for diagnostics for the cluster.

I think you can run a wire from the distributor to the back of the tach, if it works with a temporary  wire then the factory wire is probably broken somewhere inside.

If it still doesn't work, test the lead directly at the distributor to make sure the distributor has outgoing signal.

Some more experienced members will hopefully chime in.

[LTZ C20]

Oh and the printed circuit board on the back of the cluster bucket should be clean and unbroken and the harness should be clean and making good contact.

[76K20]

I thought about running a temporary wire but I'm not sure what the resistor does.   Thanks for the help LTZ

[LTZ C20]

True. If another member chimes in, they might know about the resistor, then you could just put the right resistor on a wire and try that.

[timthescarrd]

when you talking about resistor, is it a little metal canister with a wire leading in and out on the firewall like below?  I've heard these called filters, condensers, capacitors... but what they're there for is to filter out RF noise that can cause the tach to jump around.

[LTZ C20]

So there you go. Thanks to timthescarrd, you should be able to use a temporary wire without any resistors or that kinda stuff. Just for testing to see if the factory wire has gone bad.

[Irish_Alley]

hope this helps but the "tach" signal off the distributor is a "common" wire

note how when you hook a tach up to a coil you use the neg post of the coil

[76K20]

when you talking about resistor, is it a little metal canister with a wire leading in and out on the firewall like below?  I've heard these called filters, condensers, capacitors... but what they're there for is to filter out RF noise that can cause the tach to jump around.

That's exactly it. Thank you

[76K20]

hope this helps but the "tach" signal off the distributor is a "common" wire
 
I  know they were a common wire on aftermarket tachs that's why I was leery  about using a common on the factory tach not after seeing the filter on mine.

[LTZ C20]

You should be ok for testing. If you want to get a new wiring harness for the the tach, I believe that some of the major resto parts companies sells that harness pictured above.

I would first determine if that's the problem or not tho.

[76K20]

You should be ok for testing. If you want to get a new wiring harness for the the tach, I believe that some of the major resto parts companies sells that harness pictured above.

I would first determine if that's the problem or not tho.

Yea soon as I can get my truck back in the garage I'm going to run a new wire.  Got the garage filled up with guns to blue right now.

[LTZ C20]

Cool. Good luck, let us know what you find when you run the new wire. Have fun with your guns too, I know I do.