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Since the car is a 1979 removal is pretty easy and there are other diagnostic test you can perform before you send in the board.
First if you remove the tach / speedo lens cover from the tach / speedo housing and then remove the bezel. Once completed remove the three tach retaining screws... Here, go read this, it will walk you through the entire process.
Once you have the tach out you should verify power and ground on the three tach clips.... Use another ground source to test the power terminal, then use the ground clip to test again. This will verify that you have power and ground at the tachometer. Once you have done this then test continuity from the signal clip to the connector that plugs in to the filter (or distributor if by-passed). This will verify the signal wire is good. You pass all three of these test then you do need a board.
Keep in mind a board is not a fix all and as the tach ages so do the internal analog movements so it is possible for you to purchase a board and not get fixed. If you send the tach in to us for the repair we can test the movement before we install a board and know if the issue is the board or movement.
Thank you! So, $119 and I send you my tach & old board, you test it and repair it (if possible) and return it to me? Am I reading that correctly? Will I also need a filter or is that included?
I checked that. The white signal wire exits the wire harness near the firewall and runs directly to the dist (nothing in between).
Okay... then I would pull the tach and follow the test above to make sure the wire isn't broken between the tach and the distributor. Get a multimeter and check continuity from the signal clip to the end of your white wire.
Also verify you have power and ground once the tach is removed.
Once you pass these test then yes... I'd send in the tach and board. The filter is sold separately.
If you do decide to send the tach to us, please email Sales@Willcoxcorvette.com for a Repair Auth. number.
my 75 sits at 1500 with key off. goes to 0 and works correctly key on and or running. is this normal?
When new, the original tachometer was designed to hold (or closely hold) the last input. If the car was idling at 1500 when you shut it off yes that is normal.