Tach issues/diagnosis
Thread Starter
3rd Gear
Joined: Feb 2022
Posts: 4
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Tach issues/diagnosis
3rd times a charm maybe? My 76 tach wasn’t working. I replaced the tach filter and circuit board and everything worked great. Just before reinstalling in the dash it stopped working. I replaced the 10a fuse and it seemed to be working. I checked voltage on both wires and it is receiving 12v power from main wire and from tach wire. I installed it back in the dash and it zeros out, then moves when cranking but then goes to zero when it’s running. I bypassed the filter and plugged directly into distributer and it does the same thing. I opened the distributer cap and everything looks ok. I’m out of ideas. Any help on next steps is appreciated.
Thread Starter
3rd Gear
Joined: Feb 2022
Posts: 4
Likes: 0
I replaced the tach circuit board at the beginning of January. It worked when I first tested it outside the dash. A couple days later I drove it around the block to test a brake bleed and it worked for about 2 laps (maybe 3 minutes) and then stopped working on final lap. That's when I tested and it had signal from the tach wire but not the main power so I replaced the fuse. It's been like this since. It's getting main power at 12v again from the pink wire, and brown wire from tach connector to the distributer is getting 12v and getting a signal when cranking. Just when the car is running it stays at zero.
Le Mans Master
Joined: Jun 2019
Posts: 7,642
Likes: 2,463
From: Indiana
I replaced the tach circuit board at the beginning of January. It worked when I first tested it outside the dash. A couple days later I drove it around the block to test a brake bleed and it worked for about 2 laps (maybe 3 minutes) and then stopped working on final lap. That's when I tested and it had signal from the tach wire but not the main power so I replaced the fuse. It's been like this since. It's getting main power at 12v again from the pink wire, and brown wire from tach connector to the distributer is getting 12v and getting a signal when cranking. Just when the car is running it stays at zero.
Safety Car
Joined: Oct 2007
Posts: 4,360
Likes: 1,724
From: Seattle Area Washington
Probably your board...
You can check this, never know
Pull the cap and check connections between HEI module and terminal block and brown wire at 3 wire connector.
When ignition coil changes between primary and secondary windings the HEI module's internal switch opens & closes.
This is where the electronic tachometer gets it pulse signal from.
You have 12volts to the brown wire because you are reading primary side coil voltage.
You can check this, never know
Pull the cap and check connections between HEI module and terminal block and brown wire at 3 wire connector.
When ignition coil changes between primary and secondary windings the HEI module's internal switch opens & closes.
This is where the electronic tachometer gets it pulse signal from.
You have 12volts to the brown wire because you are reading primary side coil voltage.
Race Director
Joined: Nov 2006
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I put a new tach board in mine about 18 years ago, give or take. So long ago now I don't remember which vendor sold it to me. Still working fine. Perhaps you just got a bad one?
Le Mans Master
Joined: Jun 2019
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From: Indiana
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Thread Starter
3rd Gear
Joined: Feb 2022
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I thank all of you for your valuable input. I read through the thread after you sent it. I tried contacting Willcox twice via email before calling them to exchange the board. Before exchanging they had me email another email address which I also never heard back from.
I checked the continuity of the wires, the volts, fuses, distributor, starter and ended up taking everything back apart from the dash and starting from square one looking for any signs on the board it was bad. It was actually a simple fix as the bottom connector on the board was bent out of place. I’m not sure how that happened from the first time or why it worked perfectly for 5 min before stopping, But it seems to be working now.
thank you all again.
I checked the continuity of the wires, the volts, fuses, distributor, starter and ended up taking everything back apart from the dash and starting from square one looking for any signs on the board it was bad. It was actually a simple fix as the bottom connector on the board was bent out of place. I’m not sure how that happened from the first time or why it worked perfectly for 5 min before stopping, But it seems to be working now.
thank you all again.