tach/rpm on the factory cluster

[GP4U2NV]

I have a 83 regal limited.

I put a 84 t-type cluster in it.

I would like to use the tac, until I get the V8 boosted.
I have a 350 in it with the standard "white tac" wire from the distributor.

When I hook up the wires as follows:

pin A Pink/blk GAGES fuse Pos Feed (switched positive)
pin B White TACH signal (tach wire)
pin E Blk Gnd (ground)

The rpm gauge or bar graph goes to full and holds there.
I can disconnect the tach wire and when ever the key is on it goes to full reading. Is this a failure of the TAC gauge or am I missing something.

 

[SuperSix]

Was this a known-good tach when plugged into an 86/87 turbo harness?

 

[GP4U2NV]

I can not answer, it was a parts car for a guy that was restoring a 87 GN

 

[SuperSix]

Hard to diagnose if you aren't sure that the tach works in the first place.

ALL of the factory tachs are grossly inaccurate now, and unless it's been sent out for repair by Casper's - it won't be accurate anyway.
http://www.casperselectronics.com/store2/product_info.php?cPath=61_62_5_6_33&products_id=717
http://www.installationinstructions.com/103070.pdf

 

[GP4U2NV]

Can you tell me what type of signal is going into it stock?

 

[SuperSix]

Can you tell me what type of signal is going into it stock?

I have no idea. I just know that unless they have been serviced by Caspers - factory tachs are useless.

I will dig and see if I can find a wiring diagram.

 

[TurboBob]

Can you tell me what type of signal is going into it stock?

the stock ignition module produces a 12 volt square wave, 3 pulse per engine rev. This is the signal that goes to that factory tach.

Bob