Factory tach not working

[86 Silver]

Found a factory tach cluster on eBay. Putting it in my '86. Everything works but the tach! Bought new wiring harness from LMC 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.
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[ray_mcavoy]

It sounds like you probably have it connected correctly, but just to verify, the wire colors should be:

Black = Ground
Pink = +12V connection to fusebox
Brown (or White) = Coil/Distributor (TACH terminal on HEI)

If that's how you have it connected and it still doesn't do anything then it sounds like you probably got a bad tach.

[88Jimmy4x4]

verify its on the tach terminal of distributor and making good contact too, could be bad harness from LMC

[motornut]

stock the power came threw the firewall
but i wired mine to the cluster power pink striped
i'd check the tach circut board too
may have a cold soldier joint

[86 Silver]

Originally Posted by motornut

stock the power came threw the firewall
but i wired mine to the cluster power pink striped
i'd check the tach circut board too
may have a cold soldier joint

Ok, here we go again.

New tach from LMC.
New tach wiring harness (HEI) from LMC

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 Hell!?!
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[motornut]

Originally Posted by 86 Silver

Ok, here we go again.

New tach from LMC.
New tach wiring harness (HEI) from LMC

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 Hell!?!
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Gee sounds like you have it hooked up right
the ground " bus" area by the ebrake might be better
getting it to " zero" when powered is good
aside from a bad unit , should go when hooked up as described
but did any other tach work?
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[hatzie]

TACH tap off the coil is present? I've seen HEI with no tach terminal inside the cap.

[86 Silver]

Originally Posted by hatzie

TACH tap off the coil is present? I've seen HEI with no tach terminal inside the cap.

Was wondering that...will verify tonite
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[86 Silver]

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?
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[86 Silver]

Originally Posted by hatzie

TACH tap off the coil is present? I've seen HEI with no tach terminal inside the cap.

Yes it is...tested with light and it also has power.
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[mrolds88]

Double check your terminal on the wire at the dist. My crew cab drove me insane. I could start it up and it would run fine. Go to start t again, nothing but cranking. Swapped carbs, caps, modules, plugs, wires, everything but the tailpipe. Turned out that the brass part of the connector was loose, not loose on the wire, but the distributor end. The plastic was a tight enough to keep the power wire in the cap. Finally pulled the connector apart and crimped down the end and worked perfect. This might be your issue too.

[86 Silver]

Originally Posted by mrolds88

Double check your terminal on the wire at the dist. My crew cab drove me insane. I could start it up and it would run fine. Go to start t again, nothing but cranking. Swapped carbs, caps, modules, plugs, wires, everything but the tailpipe. Turned out that the brass part of the connector was loose, not loose on the wire, but the distributor end. The plastic was a tight enough to keep the power wire in the cap. Finally pulled the connector apart and crimped down the end and worked perfect. This might be your issue too.

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...
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[86 Silver]

Installed new tach after a final verification that the wiring was good. Didn't work. I made up a few words you haven't even heard yet! Started playing with the two tachs, comparing new circuit boards to old tach (found a dark did colored spot on old...it was fried).

Long story short, the circuit board can only go on one way. Then you put the little washer over each of the 4 prongs, followed by the little lock washer, then the nut. Next put on the plastic backing that screws into the cluster housing by 3 screws...then plug in wiring harness to the three prongs sticking through the backing. Screw plastic backing into housing, then screw in the tach itself.

My mistake? I put the nuts on the outside of the plastic backing to hold the tach to it...that was a bad idea apparently. The only thing holding that backing to the tach is the harness plug! Who knew!?!
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