Tach dash question, need help.

[fatblockvelle]

I have a 1971 k5 blazer... Truck did not have a tach dash in it. I just got a complete dash that looks to be in great shape with no burn marks on circuit board. My question is.

Is there a way to tell if the truck the tach dash came from is a 8 or 6 cyl?

Is there a way to make it work if it was from a 6cly?

Is it as simple as swapping out the clusters and putting a tach wire and power on the gauge?

thanks for the help!!!! Anything else i should look out for

[jjzepplin]

The tach should have a 6 or 8 on the back of it.

[fatblockvelle]

hmmm... looked all over.. did not see any stamp or tag... could be under the
"tin" ?

[Coley]

You don't have to fully install it to test it.
(note: on the back of the tach they originally had a '6 cyl' print they put on it or a GM part number....but this might be worn off now)
Do the following to test the tach:
First.....Review the back of the tach...there should be an insulated (2) prong connection in the back/centre with a clear 12V (+) indicator and a Coil or 'signal' connector. The indicators for these should be stamped into the casing.
(note: normally these connectors are at 90° to one another the way they are orientated and this would be what the tach harness normally plugs into)
Next: Run a hot/positive from your battery to the 12V (+) prong/connector.
Next: Run a wire from the - (negative) side of your coil to the 'Coil' (signal) prong connector
Next: Run a ground wire from your block to the metal casing of the tach.
Check all of these connections to make sure they are solidly connected and well insulated from one another.
Start up the truck and check the readings and rev the truck to see how much gain/rpm reads out.
All Good
Coley

[fatblockvelle]

Originally Posted by Coley

You don't have to fully install it to test it.
(note: on the back of the tach they originally had a '6 cyl' print they put on it or a GM part number....but this might be worn off now)
Do the following to test the tach:
First.....Review the back of the tach...there should be an insulated (2) prong connection in the back/centre with a clear 12V (+) indicator and a Coil or 'signal' connector. The indicators for these should be stamped into the casing.
(note: normally these connectors are at 90° to one another the way they are orientated and this would be what the tach harness normally plugs into)
Next: Run a hot/positive from your battery to the 12V (+) prong/connector.
Next: Run a wire from the - (negative) side of your coil to the 'Coil' (signal) prong connector
Next: Run a ground wire from your block to the metal casing of the tach.
Check all of these connections to make sure they are solidly connected and well insulated from one another.
Start up the truck and check the readings and rev the truck to see how much gain/rpm reads out.
All Good
Coley

good info. but what im really asking.. is do i need to do anything other than just hook the tach up when i swap clusters??? everything is plug and play

[csfields]

You need to make sure the printed circuit board is for a tach. A non tach circuit board does not have a place for the 12+ and coil wire to feed through and will not stretch enough per say to accomodate the tach under it.

[fatblockvelle]

Originally Posted by csfields

You need to make sure the printed circuit board is for a tach. A non tach circuit board does not have a place for the 12+ and coil wire to feed through and will not stretch enough per say to accomodate the tach under it.

YES I have a whole cluster now that is complete.

[davepl]

Plug it in. If you have HEI it'll be hit or miss. I'd stick one of those cheap but highly-accurate tach/dwell/volt/etc meters on it to compare and make sure it's accurate. That'll also ensure you have the right 6/8 cyl tach.

In the event the tach is wrong, they're not that expensive as a repro. You already have the cluster, PCB, all of that.

I bought this one from Amazon for 25 bucks: Amazon.com: Actron CP7605...
The scale also shows what it -would- be for a 6 cyl, so let's say it doesn't match the 8 cyl scale but does match the 6, you know what you've got.

I noticed my multimeter also has a Hz setting but was unable to get a useful signal.

[jjzepplin]

Yep and you can sell the 6cyl tach here easy in the event that it is 6cyl.