Stock tach problem
 

On my '89 i have the stock tach that sits on the dash... when goin down the road and gaining speed it bounces all over the place and goes all the way down to 4 grand.. how can i go abut fixin it? and it can be replaced with a aftermarket one right? thanks

It's not a stock tach. 89's never came stock with a tach. Is it one like the one on the right? Attachment 38576
If so it has a sensor strapped to your trucks alternator, If it comes loose it'll bounce around.

I cant figure out how to download a picture when replyin to in a thread... but no mine dont look like that one... and it runs down to the harmonic balancer.

Actually, all 1st Gen's had the option to have a tach installed by the dealer. Most people just call them factory tachs though. They look like this...

Attachment 38573

So it's entirely possible his '89 has that tach.

I hate to break it to you but 91.5-93 trucks came with the dealer installed tach option. A 89-early 91 doesn't even have a crank sensor.

OP your truck must have something like a dakota digital tach setup then.

I'll say it again, the Non-Intercooled trucks could be ordered with tachometers just like the one pictured. That's why when you're in the market for a "factory" tach you need to look at the wiring, because there are two different types, one for the Non I/C trucks (and early intercooled) and another for the later intercooled trucks.

I've seen in person, quite a few Non Intercooled trucks with the factory tach set-up, two of those trucks were still owned by the original owners who told me they specifically ordered the tach.

Do some research the non intercooled trucks did not come with a factory tach. I had a 90 there is no crank sensor on them to run a tach even if you wanted too.

I blew that crap out of the rad in my 90 so I had it ripped apart, There is no crank sensor on a 80-91. Isspro lists a tach wiring harness for non intercooled trucks as a aftermarket upgrade. I know lots of people with non intercooled trucks aswel as there has been about 5 in the family not one had a factory tach.
Attachment 38567

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That was like 2 minutes of searching.

My tach looks like the one peobryant pictured and the person i bought the truck from said that is was installed at the dealership when the original owner bought it.

I dunno how because it's not possible.

ok well i do appreciate the the input but thats what i got on it. so guess i'll just keep lookin