My OEM style reproduction tach goes up in smoke

[smorg007]

Hi gang,

I reached out for help on this forum to prevent this costly mistake, what went wrong. I installed an OEM reproduction tach in my truck. The only difference is my truck has been upgraded to mid 70's HEI distributor. On the supplied Brn/Pink wiring harness I swapped out the round connector for a female spade connector and hooked the brown wire up to the male spade terminal on the HEI Coil labeled "TACH" instead of the "-" side of the stock coil. I then connected the pink wire inside to the fuse box to the "IGN UNFUSED" connector. Connected the other end "V-shaped" connector to back of tach and started the engine. Tach worked perfectly. (Even close to accurate) I drove truck back to my home about 2 miles away and everything was good to go. Have not driven the truck until yesterday. Pulled it out of the garage and let it warm up, tach working just fine. Approximately 10 minutes went by and I drove towards town but only made it another 2 miles when I smelled something burning. I looked down at my tach and noticed the glass face over the tach was full of smoke and the tach was reading "0" and stopped functioning. I pulled over immediately and unplugged the pink wire from the fuse block. "WHAT WENT WRONG"
I searched the threads and read these http://67-72chevytrucks.com/vboard/s...archid=2110180 that indicate everything is compatible with HEI. Another tach gauge is $100+ and I do not want the same results.

What can I do to determine what went wrong and what to do to prevent this from reoccurring again. I'm hoping my lesson can be used from another member ending up with my tach up in smoke results. I spent the money on the upgrade conversion to enhance the looks to my show truck.

[smorg007]

TTT, anybody

[71swb4x4]

There has been some talk of the repo's not working with HEI. I have no idea why. You may want to go with an original the next go-around.

[Lee H]

I'm using a repo with HEI. I suspect you have a bad unit.

[72 tigger]

I agree with Lee H. I have a repo with HEI & never have had a problem. If it was wired wrong it seems like it would have fried it immediately.

[red71cheyenne]

sounds like you may have gotten a poor repo. I am running both on HEI's and haven't had any issues. The 71 has a repo on the TPI with HEI and the Blazer has an original with HEI. No issues yet. I would try to get a replacement unit from where you bought it as you connected it right.

[vectorit]

Sounds like a defective tach to me.
I am running a new reproduction tach, and my ignition is an electronic Pertronix set up.

Is the wire harness new or the original? You may want to give M&H wire a call, and ask for Darren in tech support. Tell him what you got, and what has happened. He may have some suggestions, since they make the wire harnesses for our trucks. They also make harnesses set up for HEI upgraded ignitions, so he may shed some light on possible causes?

Just a thought...

[matthew20061]

I agree that does sound like a defective tach gauge. I've got a reproduction factory tach in mine and its hooked up to the PCM and it works perfect off of that. Where did you buy it maybe you can return it and say its defective?

[smorg007]

Thanks and continue the suggestions. I bought the complete tach upgrade kit from Tim Tygart's Obsolete Chevrolet Parts Co. If I remember correctly I paid $269.00 for the kit. It came with tach, all the required metal housing, new lens, printed circuit board, and wiring harness with easy to follow install directions. The answer to one of the questions asked about my wiring harness. I used the one that came in the kit.
Is there any test I can do on the tach once I tear it back down and remove it. Are there any resistors or circuitry I can maybe replace or repair on the tach itself.

[smorg007]

Ttt

[70Custom10Nut]

"New" doesn't always mean good nowadays. Was it made in China? I hope kept the reciept. You should be able to work something with the vendor you bought it from. You might call them and find out how many other problems they've had with the same tach. I'm glad to hear you didn't cremate your truck, and hope things work out for you.

[MT71c-10]

OH no. You let the smoke out of it.

I have not found an electrical smoke refill kit yet, and once the original smoke has dissapated into the air, it is lost forever. You will need to find which gizmo lost the smoke and replace with a pre-filled replacement.

I would guess there is a small board in the tach which something either backfed or was not correct from the factory. Replacing gizmos in electrical boards is not easy, if even possible.

And then you will have the fun of trying to return an electrical item that has been installed. Best of luck.

However you could tell them, that their electrical supplier did not fill the smoke to the required charge, which caused the factory smoke charge to heat up and leak,, therefore making it look like you "let the smoke out"!

[smorg007]

Keeping my fingers crossed. I had a pleasant conversation with a representative from Tim Tygart's Obsolete Chevy Parts Co. this morning. It was agreed that the tach should not have gone up in smoke after install and working fine. This particular tach did not come from their normal tach supplier due to being on back order. So they ordered from someone else to fill the order in a timely manner. They are contacting the supplier to help with a resolution and then will recontact me with the results. I'll keep you posted.

[68Stepbed]

Mine didn't go up in smoke, but it quit working a couple months after installation. Actually, it started acting up and bouncing all over the place at first, then finally just quit all together. I guess it was just defective also, but it's been a couple years since I put it in and just haven't bothered with fixing it, or doing anything with it.

[71c10bbsuper]

yea my repop went up in smoke just like yours after just a few hours(hadn't even driven the truck yet) i'm running pertronix 12 volt system with the m&h wiring for an hei set up,replaced with another repop and so far no trouble.
must have had a bad batch come in on the boat!!!!
good luck