Tachometer kills the engine

[K10-Kansas]

When I connect my tachometer wire to my tach and distributor, my engine dies. If I connect the tach to the dizzy it won't start.I have the 2 male blade tachometer that comes stock in the stock cluster. My HEI came preinstalled on my Blueprint engine.

1. My multimeter shows continuity from the cab terminal end of the tach wire to the the engine bay terminal of the tach wire showing the wire is not interrupted.
2. My 12v wire to my tach shows 12v.
3. My coil blade on the tach shows O.L. when trying testing to any part of the metal housing, mounting post etc. on the tach and gauge cluster proving that the tach isn't grounding out to itself.
4. My tach wire shows O.L. on the multimeter when connecting the multimeter to a ground proving that my tach wiring is not grounding out

Is it possible that some HEI distributors will not work with a reproduction of original equipment 1971 tachometer. The truck did not have a tach when I bought it and also I put in a new engine and distributor when I bought it so I've never seen a working setup in the truck .

['68OrangeSunshine]

Originally Posted by K10-Kansas

When I connect my tachometer wire to my tach and distributor, my engine dies. If I connect the tach to the dizzy it won't start.I have the 2 male blade tachometer that comes stock in the stock cluster. My HEI came preinstalled on my Blueprint engine.

1. My multimeter shows continuity from the cab terminal end of the tach wire to the the engine bay terminal of the tach wire showing the wire is not interrupted.
2. My 12v wire to my tach shows 12v.
3. My coil blade on the tach shows O.L. when trying testing to any part of the metal housing, mounting post etc. on the tach and gauge cluster proving that the tach isn't grounding out to itself.
4. My tach wire shows O.L. on the multimeter when connecting the multimeter to a ground.

Is it possible that some HEI distributors will not work with a reproduction of original equipment 1971 tachometer. The truck did not have a tach when I bought it and also I put in a new engine and distributor when I bought it so I've never seen a working setup in the truck .

I heard the Pertronix Ignitor III would not work with electronic tachs. Something to do with it being a multi-spark discharge.
I have a GM HEI and an AutoSun tach. works fine.

[geezer#99]

Post a pic of the wiring where it clips into the distributor.
The wrong connectors can cause your problems.

[LockDoc]

-
If you need any tach repairs done this is a good place. I purchased a six cylinder tach components from them and put in a non working 8 cylinder case. it worked good.

https://www.cajuntachshop.com/

LockDoc

[K10-Kansas]

Originally Posted by geezer#99

Post a pic of the wiring where it clips into the distributor.
The wrong connectors can cause your problems.

Ok, I'll do that when I get home. Thanks.

[K10-Kansas]

Originally Posted by LockDoc

-
If you need any tach repairs done this is a good place. I purchased a six cylinder tach components from them and put in a non working 8 cylinder case. it worked good.

https://www.cajuntachshop.com/

LockDoc

Thanks Good to know

[K10-Kansas]

I called LMC and they said that their technician states that the tachometer does work with HEI. They said the supplier is Counterpart Auto if I want more info.

The American Auto wire technician said to put the positive lead of the multimeter on the terminal end of the coil wire in the engine bay and the negative lead of the multimeter on the battery negative, set to ohms and should get a value above 100 and if not then the tech is shorted.

[K10-Kansas]

I wonder if something like this will fix my issue with the truck not starting when the tach is connected https://www.wc-autoparts.com/blog/19...ition-systems/

[K10-Kansas]

Originally Posted by LockDoc

-
If you need any tach repairs done this is a good place. I purchased a six cylinder tach components from them and put in a non working 8 cylinder case. it worked good.

https://www.cajuntachshop.com/

LockDoc

Thanks. I went ahead and sent them a message.

[K10-Kansas]

Originally Posted by geezer#99

Post a pic of the wiring where it clips into the distributor.
The wrong connectors can cause your problems.

Here's the picture of the coil wire female connector.

[geezer#99]

Figured that’s what you had.
You need one like that but only insulated,
The ones you have short out too easily.
Like these.


https://www.pcboard.ca/spade-termina...-250-insulated

[K10-Kansas]

Originally Posted by geezer#99

Figured that’s what you had.
You need one like that but only insulated,
The ones you have short out too easily.
Like these.


https://www.pcboard.ca/spade-termina...-250-insulated

I have some of those and can put them on. I took them off so I could better see that I was actually connected when I couldn't get the truck started before I realized that if I disconnected the tach, the truck started fine.

[K10-Kansas]

There's no chance that it would help if I ran a ground wire to this post right?

[jjzepplin]

Subscribed for a solution and related information.

[K10-Kansas]

Classic Parts America has a stock tachometer
https://www.classicparts.com/mobile/...ctinfo/24-754/
and they say it doesn't work with HEI distributers so I may be out of luck trying to use my stock tachometer on an HEI. I don't want to change my HEI because it was tweaked by Blueprint to specifically work well in this engine so I guess I'll have to go look for a tach that works with HEI, 3 and 3/8ths big that looks similar to stock gauges.

[Steeveedee]

Guess I got lucky. I put in an HEI (Mallory but looks like a GM unit) and the tach works. Sun Supertach II.

[K10-Kansas]

Originally Posted by Steeveedee

Guess I got lucky. I put in an HEI (Mallory but looks like a GM unit) and the tach works. Sun Supertach II.

Hey Steve did you mount your tach in the stock housing?

[Steeveedee]

No, it's on the driver's side a-pillar. That's where my FiL mounted it. There is a vacuum gauge in the tach hole.

[Alloyvert]

This adapter was mentioned in the thread linked below and can supposedly adapt any tachometer to any style ignition.

https://67-72chevytrucks.com/vboard/...ght=tach-adapt

Direct link to the product https://ashlocktech.com/store/ols/products/tach-adapt

[K10-Kansas]

Originally Posted by Alloyvert

This adapter was mentioned in the thread linked below and can supposedly adapt any tachometer to any style ignition.

https://67-72chevytrucks.com/vboard/...ght=tach-adapt

Direct link to the product https://ashlocktech.com/store/ols/products/tach-adapt

Thanks, I sent them a message.

[Richard]

I am a simple thinker. Know that grounding the tach wire will kill the engine, Infact some have installed a switch to do this for an ani theft device. Would think that something is grounded in the circuit. I would investigate if it is a wire, the tach or?

[K10-Kansas]

Originally Posted by Richard

I am a simple thinker. Know that grounding the tach wire will kill the engine, Infact some have installed a switch to do this for an ani theft device. Would think that something is grounded in the circuit. I would investigate if it is a wire, the tach or?

Yeah, I should reinstall my cluster and see if there is continuity between the coil blade on the cluster and a good ground.

[K10-Kansas]

Originally Posted by geezer#99

Figured that’s what you had.
You need one like that but only insulated,
The ones you have short out too easily.
Like these.


https://www.pcboard.ca/spade-termina...-250-insulated

You nailed it! I put the cover on the female connector and it started and registered RPMs! The freaking tach connector had been touching the 12v connector. Thanks!

[geezer#99]

It’s always the little things, isn’t it!

[MySons68C20]

Great post!!