Ground wire kills the tach...

[Ian Reppert]

I’ve got a winter project after yesterday afternoon... I installed some LED taillights from CU Layer and now my tachometer is not working. This isn’t a complaint about CU Layer (install was easy and the lights work flawlessly). I had to change my old turn signal flasher unit out so it would work with the LED’s. It required a ground wire connection to operate properly. Once I did this, the tach stopped working. Here’s my talk group question: Would this be connected to the turn signal flasher unit through the tachometer (for the indicator lights at the bottom)? Or, have I opened up a circuit by grounding the flasher unit? If I put the old flasher unit back in, the tach works fine.
The details
1962 B Coupe,
Early T6 model.
Memotronics flasher unit recommended by CU Layer.

[Mike Wilson]

I'm assuming electric tach. I have the same set up in my '63 coupe: electric tach, CULayer rear tail lights and an electronic flasher that required grounding. No problems with the tach.

I would double check the wiring connections on the back side of the tach to make sure they are correct. Hopefully someone can post the color diagram from Joe Leoni's book.

Mike

[Ian Reppert]

Mike, yes electric tach. The needle of the tach also bounced when the turn signal was on (prior to the new tail lights), so I’m assuming that someone crossed some wires long ago and now I’m going to fix it. I haven’t pulled the tach out yet, I ran out of time yesterday. If someone can post the schematic, that would be great. I’m going to order Joe’s book in case it isn’t as easy as a misplaced wire.

[Mike Wilson]

I just Googled "356 Porsche electric tach diagram" and found a lot of info.

Mike

[Doug McDonnell]

Since you don't know how your tach was energized (how it was wired up) I would encourage you to use the spare wire in the harness that in the engine compartment will be wound up near your Voltage regulator. If you have one. Not sure if a 62 has one. If you do the other end is under the dash and is the only unpaired wire in the multi connecter. I did read that Power for an electric tach in a car with retrofit is from the blue/yellow wire for instruments. Hope this helps. viewtopic.php?t=31536

[Doug McDonnell]

Back of Tach has #1 and #15 terminals. #1 connects to coil + and #15 to #15 on ignition or yellow/green wire

[Ian Reppert]

Thanks for the help guys. I think it’s going to be tracing down a wire that has been installed in the wrong place. I’ll keep you updated and post a picture if I find something weird.

[Doug McDonnell]

I agree Start with where #15 on tach is wired to.

[Martin Benade]

My first check would be to verify a good ground to the tach housing.

[Doug McDonnell]

Works fine with the original relay so doubt a ground issue. But who knows?

[Martin Benade]

I agree, but bad grounds cause odd things to happen, and it’s quick to check. And if turn signal had some ill effect on the tach before, something’s up.

[Mike Wilson]

Ian, you indicated the tach bounced before the installation of the LED lights so that leads me to believe Martin's suggestion is one to follow up on.

Mike

[Al Zim]

Your problem is not with the tachometer the situation exists because the current flow through the turn signal flasher is backwards. switch the wires from side to side on the power to the turn signal flasher.
It is my guess your car has had a new wiring loom incorrectly put in it. al zim