Problem with installing a factory tach

[89 Blazzer]

I hooked up a factory tach and when I start up, the needle goes past 5000 rpm and points straight down and doesn't move when I rev it up. I hooked up an aftermarket tach to the same leads and it reads correctly. I do not know what year the factory tach is out of, but mine is an '89. Has anyone had a problem like this or know what may be wrong? The guy I got it from swore it worked when he took it out the original truck.

 

[DMK]

Check for a good ground. If not tach may be bad. Leads may be different on factory tach. Check a shop manual wireing diagram.

 

[newyorkin]

Was it a V8 truck that this tach came out of? Needle going all the way to the end indicates the incorrect connections, I think. Make sure the power to the tach and the coil lead aren't accidentally swapped at the back of the tach. Does it change when you turn on and turn off, or did it shoot up once and stay there?
This may be stretching (don't know what your acquisition situation was or anything), but can you re-install it in the old truck to verify it wasn't damaged? It just wires up differently than the aftermarket tach, too.

Is there any way you can get a hold of the printed circuit or look at the wiring from the truck it came from? Are you using that printed circuit, or wired straight into it? Could there be a short somewhere on the board?

Ratch
<a target="_blank" href=http://k5.8m.com>k5.8m.com</a>
**Your ad here**<P ID="edit"><FONT class="small">Edited by newyorkin on 08/09/01 09:52 AM.</FONT></P>

 

[hoserr]

i have a '74 an my tach is outta of '79 diesel 'Burb, got all the info from the library, paid a few cents for coping an now i can trouble shoot it when ever i need to.

'74 350,t-400/205,d44(L/S),12b(detroit)cutout doors, thrashed an twisted

 

[pcorssmit]

What happens w/the ign on, not running?

Pete

'83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
'97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd

 

[89 Blazzer]

Thank you for your replies. I will answer all of the questions in this post.
DMK: The connections are labeled on the back of the tach. I hooked directly into the fuse box for 12v, directly to the lead on the coil that is for the tach and grounded to a metal bracket under the dash. I am going to check the ground again, maybe even try a different spot.

Newyorkin: I don't know what it came out of. It is hooked up according to the markings on the tach. When the ignition is turned on it is at 0, when I start it, it climbs. When it is starts running, it goes past the max. When I shut the truck off, it returns to 0. It is wired directly into the tach, not the printed circuit.

pcorssmit: when the ignition is on, it reads 0. If I move the needle with my hand, it returns to 0 when the key is turned on.

Like I said earlier, I am going to look closer at the grounding.

 

[Michael]

Hey Tony, if the tach turns out to be bad I can probably fix it for you....if no one closer can. I'm in Texas. I have worked on lots of them...all the advice you've gotten so far sounds good. Hope it's just a ground and everything works out OK.

Michael

<a target="_blank" href=http://www.jmartin.net/parker/goose.htm>www.jmartin.net/parker/goose.htm</a>

 

[89 Blazzer]

Thanks for the offer Micheal. I know you can not be too precise since you do not know what is wrong, but if it is the tach, what kind of price range do you think you would charge? I will not hold you to it if I have you take a look at it!!! Just want a ballpark or better estimate. What do you think may be wrong with it?