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Sat Apr 28, 2018 2:17 pm

NHS has recently converted the inoperable clock from my ‘64’s dash into a tach that matches the speedo. :) I’m ready to tackle the installation job, but I need some guidance from you electrical gurus to make sure I hook it up correctly and as efficiently as possible.

The research I’ve done recommends wiring the tach as follows:

Power....tap into a switched power wire behind the instrument panel
Coil.....run a new wire and connect to the coil
Ground...any good ground behind the instrument panel

For power, I plan to use a posi-tap. Referencing the attached wiring diagram, which wire would be best to tap into?

For the wire to the coil, I’m thinking I’ll attempt to fish it through the the OG harness tube that runs from the luggage compartment to the engine compartment on the right side of the car behind the rocker panel. Is this doable? Or, is there a better/easier way to run this wire?

Referencing the diagram again, which coil post should this wire connect to? (i’m running a Pertronix breakerless ignition if that makes a difference)

For ground, I plan to connect to the same tab that the wiper motor is grounded to. Is this ok, or is there a better place to connect to ground?

Sat Apr 28, 2018 2:29 pm

For what it is worth .......

Any of those in line wire splices that cut your insulation and grasp the wire (often while cutting a few strands in the process) are garbage!

They destroy good wires, they let in corrosion causing elements and quite simply should be avoided.

Run a wire to your fuse panel, use a "piggyback" spade connector and do it properly.

https://www.amazon.com/Ancor-210613-Electrical-Mal...connectors

Dave

Sat Apr 28, 2018 2:31 pm

Read your tach manual, many units have a 4/6/8 cylinder setting.

Dave

Sat Apr 28, 2018 6:13 pm

If you're not sure how you'll run a wire from the tach back to the coil, you can use the car's existing wire harness instead of trying to snake a new wire back thru the car.

VW gave each tail light it's own separate fuse & wire and you can use one of these for the coil/tach connection. You'll need to remove the tar board panels in the engine compartment to expose the tail light wiring. The idea here is to run a jumper wire connecting the two tail lights together and have them both run off one fuse. This frees up one wire to carry the signal from the coil up to the tach.
First, disconnect the grey/black wire from the left tail light and extend it to reach the #1 terminal on the coil (the same one where the wire from the distributor connects). Then connect the two tail lights together with a jumper wire which can run behind the engine, preferably under the firewall tarboard. Now, at the back side of the fuse box, disconnect that same grey/black wire from it's terminal (3rd from the right on that wiring diagram above) and run it to the signal connection on the tach.
Now you're good to go without drilling any new holes in your car.

I've been running this setup for years with no problems.

Sat Apr 28, 2018 8:10 pm

When I neared he end of my body-off restoration, I ran 5 extra wires down the RH side of the car and later used one for the tach.

What would I do if I were to have do the job now without those wires?

I would run the wire along the floor under the carpet and next to the brake fluid line to the back. I would protect the wire under the car (from where it exits the cabin to where it enters the engine compartment) with a suitable conduit (commonly used by electricians and also by VW).

Sun Apr 29, 2018 3:27 am

kiwighia68 wrote: When I neared he end of my body-off restoration, I ran 5 extra wires down the RH side of the car and later used one for the tach.

What would I do if I were to have do the job now without those wires?

I would run the wire along the floor under the carpet and next to the brake fluid line to the back. I would protect the wire under the car (from where it exits the cabin to where it enters the engine compartment) with a suitable conduit (commonly used by electricians and also by VW).

This! ^^^^

If that tach wire gets abraded and makes ground, the engine will behave exactly as if you turned off the ignition key while driving....... stop running and not restart until the ground point is located and remedied.

Dave

Sun Apr 29, 2018 10:10 am

On my 64 I put a piece of plastic tube (truck air brake tubing) down inside the driver side door post,then fed a bunch of extra wires from fuse panel area down the tube,through a grommet at the bottom of the door post,and beside the sill plate to the back of the car.As was mentioned,the wire must be protected from damage,hence the plastic tube.Car is not finished yet,but I may try running the wires under the sill plate,as was done on later cars.The air brake tube is handy stuff and comes in several different sizes.Available at your local big truck repair place.

Sun Apr 29, 2018 10:40 am

I'm a firm believer in a diode across the tach 'input' and ground for a steady tach needle. When I put one on my tach, the needle became rock steady. Just sayin'

Sun Apr 29, 2018 1:18 pm

runamoc wrote: I'm a firm believer in a diode across the tach 'input' and ground for a steady tach needle. When I put one on my tach, the needle became rock steady. Just sayin'

What type of diode do you recommend?

Sun Apr 29, 2018 1:20 pm

rcooled wrote: If you're not sure how you'll run a wire from the tach back to the coil, you can use the car's existing wire harness instead of trying to snake a new wire back thru the car.

VW gave each tail light it's own separate fuse & wire and you can use one of these for the coil/tach connection. You'll need to remove the tar board panels in the engine compartment to expose the tail light wiring. The idea here is to run a jumper wire connecting the two tail lights together and have them both run off one fuse. This frees up one wire to carry the signal from the coil up to the tach.
First, disconnect the grey/black wire from the left tail light and extend it to reach the #1 terminal on the coil (the same one where the wire from the distributor connects). Then connect the two tail lights together with a jumper wire which can run behind the engine, preferably under the firewall tarboard. Now, at the back side of the fuse box, disconnect that same grey/black wire from it's terminal (3rd from the right on that wiring diagram above) and run it to the signal connection on the tach.
Now you're good to go without drilling any new holes in your car.

I've been running this setup for years with no problems.

Thanks, I think I’ll try this approach

Sun Apr 29, 2018 1:50 pm

FL-Frank wrote: runamoc wrote: I'm a firm believer in a diode across the tach 'input' and ground for a steady tach needle. When I put one on my tach, the needle became rock steady. Just sayin'

What type of diode do you recommend?

I found other threads on here recommending 1N4005. Yes?

Sun Apr 29, 2018 4:45 pm

Quote: 1N4005. Yes?

Yes, that will work. Also, 1N4001 will work. The 1N4001 has a (PIV) Peak Inverse Voltage rating of 50 volts. The 1N4005 has a PIV rating of 600 volts. Both are 1 amp rated. Both will work with 'room' to spare.

Sun Apr 29, 2018 4:56 pm

runamoc wrote: Quote: 1N4005. Yes?

Yes, that will work. Also, 1N4001 will work. The 1N4001 has a (PIV) Peak Inverse Voltage rating of 50 volts. The 1N4005 has a PIV rating of 600 volts. Both are 1 amp rated. Both will work with 'room' to spare.

So, connect an inline diode to both the input or signal wire and the ground wire?

Sun Apr 29, 2018 6:05 pm

Quote: So, connect an inline diode to both the input or signal wire and the ground wire?

Sorry, I had a brain fart. :oops: The diode goes in series with the signal from the coil to the tachometer. Not connected to ground. Crimp a butt-splice connector on the end of the diode with the silver band. Crimp another butt-splice connector on the other end of the diode. Crimp the end of butt-splice connector to the wire connected to the ignition signal source. Connect the butt-splice, nearest the silver band, to the input of the tach. In other words, cut the wire coming from the coil to the tachometer and splice in the diode with the silver band towards the tachometer. This is correct, I swear.

Sun Apr 29, 2018 6:19 pm

runamoc wrote: Quote: So, connect an inline diode to both the input or signal wire and the ground wire?

Sorry, I had a brain fart. :oops: The diode goes in series with the signal from the coil to the tachometer. Not connected to ground. Crimp a butt-splice connector on the end of the diode with the silver band. Crimp another butt-splice connector on the other end of the diode. Crimp the end of butt-splice connector to the wire connected to the ignition signal source. Connect the butt-splice, nearest the silver band, to the input of the tach. In other words, cut the wire coming from the coil to the tachometer and splice in the diode with the silver band towards the tachometer. This is correct, I swear.

Thanks. Rather than running a signal wire from front to back, I’m going to utilize the tail light wiring as recommended by rcooled. Should I add the diode in the engine compartment near the coil or in the luggage compartment near the tach?

Sun Apr 29, 2018 9:02 pm

What??
What tach do you have? It’s like 9 ft from the coil to the dash. It should take you 10 minuets. Diode? Huh. Just run the wire. It took me literally 2minutes.
All the wire runs should be easy under the carpet from the main harness.

It’s an old Volkswagen for Christ sake. Not a maybach. You probably have horrible wiring all over the place. :lol:

Mon Apr 30, 2018 2:52 am

trelms wrote: What??
What tach do you have? It’s like 9 ft from the coil to the dash. It should take you 10 minuets. Diode? Huh. Just run the wire. It took me literally 2minutes.
All the wire runs should be easy under the carpet from the main harness.

It’s an old Volkswagen for Christ sake. Not a maybach. You probably have horrible wiring all over the place. :lol:

The car was completely rewired per the factory wiring diagram when it was restored 3,500 miles ago.

Mon Apr 30, 2018 5:00 am

Quote: in the luggage compartment near the tach?

It's where I installed mine. Also, cover the whole thing, connections and the diode, with some heat shrink tubing, or just wrap it in tape.

Mon Apr 30, 2018 5:12 am

FL-Frank wrote: trelms wrote: What??
What tach do you have? It’s like 9 ft from the coil to the dash. It should take you 10 minuets. Diode? Huh. Just run the wire. It took me literally 2minutes.
All the wire runs should be easy under the carpet from the main harness.

It’s an old Volkswagen for Christ sake. Not a maybach. You probably have horrible wiring all over the place. :lol:

The car was completely rewired per the factory wiring diagram when it was restored 3,500 miles ago.

Oh. Hahha. Yeah I just saw the gallery. Do it the right way :lol:

Mon Apr 30, 2018 5:14 am

rcooled wrote: If you're not sure how you'll run a wire from the tach back to the coil, you can use the car's existing wire harness instead of trying to snake a new wire back thru the car.

VW gave each tail light it's own separate fuse & wire and you can use one of these for the coil/tach connection. You'll need to remove the tar board panels in the engine compartment to expose the tail light wiring. The idea here is to run a jumper wire connecting the two tail lights together and have them both run off one fuse. This frees up one wire to carry the signal from the coil up to the tach.
First, disconnect the grey/black wire from the left tail light and extend it to reach the #1 terminal on the coil (the same one where the wire from the distributor connects). Then connect the two tail lights together with a jumper wire which can run behind the engine, preferably under the firewall tarboard. Now, at the back side of the fuse box, disconnect that same grey/black wire from it's terminal (3rd from the right on that wiring diagram above) and run it to the signal connection on the tach.
Now you're good to go without drilling any new holes in your car.

I've been running this setup for years with no problems.

I did this for my tach as well. Easy to tackle.