Factory tach in cluster not working

[86silver]

Found a factory tach cluster on eBay.  Putting it in my '86.  Everything works but the tach!  Bought new wiring harness for tach.  One wire to distributor.  One wire grounded.  Other end had pigtail that didn't plug into my harness so cut off and spliced on male end plugging in directly to fuse panel.  Plugged in to back of tach....nothing.

Thoughts?  Bad tach??  No clue if it worked when I bought it, but was told it did.

[Jason S]

It could very well be just what you said, a bad tach.

Just running through the list of things to check:  Do you have 12v power to the tach when the ignition is in the "ON" position?  Is the wiring connected to the tach terminal on the distributor, and is it a good clean connection?  Same on the other end of the distributor wire...  Lastly, is the ground connection to a good clean piece of metal?  If none of those are the culprit, then you may need to send it off for a rebuild (or find another tach gauge). With the tach out, you should be able to hook everything up using jumper wires and alligator clips to run your tests.

[bd]

In addition to Jason's post, 12-volt ignition should be the pink wire, ground should be black, and distributor pulse (tach) should be brown.  You can verify distributor pulse using a test light connected between ground and the Tach terminal of the distributor - the test light should brighten as RPM increases.

[Captkaos]

Buyer beware.  Lots of these are sold on ebay and don't work.  Verify with the buyer that it they have hooked it up and works.  you don't have to install it to test, just hook it up to the plug in the distributor cap.
When I used to sell them on ebay I would send a video of it working.

[86silver]

Ok, here we go again.

New tach.
New tach wiring harness (HEI) 

Brown wire (connector on harness verified sound) to  firewall (back outside) port on distributor.
Pink wire to secondary "iGN" spot in fuse box.  (Verified hot due to accessory flood lights plugged into other half of same port...lights work when turned on.
Black wire connected to one of the gas pedal mounting bolts.

Turned on for first time...tach twitched (old one didn't even do that).
Turned over engine...tach jumped up to 2k and then back down to flatline

What The heck!?!

[bd]

...Brown wire (connector on harness verified sound) to  firewall (back outside) port on distributor.
Pink wire to secondary "iGN" spot in fuse box.  (Verified hot due to accessory flood lights plugged into other half of same port...lights work when turned on.
Black wire connected to one of the gas pedal mounting bolts.

Turned on for first time...tach twitched (old one didn't even do that).
Turned over engine...tach jumped up to 2k and then back down to flatline

Look at the image, below.  To which distributor terminal did you connect the brown tach wire?

Don't assume the circuit connections are good.  Test and verify each circuit connection using a test light.  Verify the tach signal, as well.  If 12-volt ignition, ground and tach signal are good, contact the tach vendor.

[86silver]

Thank you for the diagram.  Yes I did use the correct connection on the distributor.  Is it possible when I put in the new coil I didn't get one with the tach setup?  Grasping here...

[bd]

Thank you for the diagram.  Yes I did use the correct connection on the distributor.  Is it possible when I put in the new coil I didn't get one with the tach setup?  Grasping here...

Tach signal from the TACH terminal is inherent with HEI.  When you replaced the coil, did you reinstall the short ground strap under the cap dust cover?

[86silver]

I will verify the ground strap.  I think I did 2 weeks ago when I installed new manifold gaskets but ill have to make sure.  Each time when cold it jumps right up to 2k but then goes below 0...strange deal

[86silver]

Ok, ran test light.  Started truck, probed TACH port on distributor...lit up.  Probed fuse panel where I have it hooked up...lit up.

Up next...take apart dash...again...and probe other end of pigtail on back of tach?

[bd]

Ok, ran test light.  Started truck, probed TACH port on distributor...lit up.  Probed fuse panel where I have it hooked up...lit up.

Don't forget to verify your ground.  Once you've verified power, ground and signal to the tach, call the vendor for support.

One last thing; does the tach have a switch to set the number of cylinders and is it set correctly? 

[86silver]

Ok, ran test light.  Started truck, probed TACH port on distributor...lit up.  Probed fuse panel where I have it hooked up...lit up.

Don't forget to verify your ground.  Once you've verified power, ground and signal to the tach, call the vendor for support.

One last thing; does the tach have a switch to set the number of cylinders and is it set correctly?

No the new   tachs don't have such a dial.  Took dash apart for 5000th time and ran test light on that end of the distributor wire....no light.  Ran test light on that end of power wire...light.  I may have found my problem.  I'm gona run a jumper wire tomorrow & see if I have a bad wire in my new   wiring harness.......

[86silver]

Ran a bypass wire from distributor to tach...test light said YES....so wiring harness had a bad wire.

Ran test light on 12v wire at tach end...test light said YES.

Ran ground to bolt that goes through firewall under dash...scraped paint off under bolt to ensure good contact.

Tach still is dead in the water!!!  Called  ...getting a new tach...

[bd]

Ran a bypass wire from distributor to tach...test light said YES....so wiring harness had a bad wire.

Ran test light on 12v wire at tach end...test light said YES.

Ran ground to bolt that goes through firewall under dash...scraped paint off under bolt to ensure good contact.

Tach still is dead in the water!!!  Called  ...getting a new tach...

Hopefully the replacement tach will solve it. 

FYI - To check the pigtail 'ground' using your test light, clip the test light to B+ and probe the ground wire at the tach end.  That will verify the entire ground path is good.   

[86silver]

Ran a bypass wire from distributor to tach...test light said YES....so wiring harness had a bad wire.

Ran test light on 12v wire at tach end...test light said YES.

Ran ground to bolt that goes through firewall under dash...scraped paint off under bolt to ensure good contact.

Tach still is dead in the water!!!  Called  ...getting a new tach...

Hopefully the replacement tach will solve it. 

FYI - To check the pigtail 'ground' using your test light, clip the test light to B+ and probe the ground wire at the tach end.  That will verify the entire ground path is good.   

Thank you...however I don't understand what you mean by "B+"?  What is that?