'67 SV Tach Wiring

[DanR]

OK Guys,

I'm stumped again !

I am trying to get my Tach (Original) wired. I've even tried two of them.

Wire from #1 Terminal on Ign Switch to the "spade" on the Tach. Then, White wire one end (with loop) to the Coil wire and one end to the #2 terminal of the Ign switch. Grounded! But no response when the engine is running.

What might I be doing wrong?

Any suggestions?

 

[sunbby]

I believe from the factory the Tach power (spade connection) was also a white wire connected to terminal #2 of the ignition switch (switched battery). Although it should work with it connected to terminal #1 (unswitched battery). Your tach will just have power going to it all of the time.

The most likely issue is the loop connection and/or a non-stock coil-ignition setup. the direction of the loop is important and there is a little metal u-shaped piece around the loop that helps couple the signal into the tach. If the loop direction is wrong or the metal piece is missing/not connected well, you will get no reading.

Did you re-wire or are you hooking up existing wiring?

I assume Tom H will have some advice too and can help get you sorted.

@Tom, I think we need to come up with a Tach FAQ Maybe elaborate on the connection part of your tach upgrade article?

 

[DanR]

I am re-wiring as you can tell from prior post.

I am utilizing the original white wire and the loop with the plastic piece and the metal fastener. It will go only one way(if used as original ?). I attempted to make sure that it made good on both contacts.

The "non-stock coil-ignition setup" might be the problem in that I have the Petronnix Flamethrower distributor and coil. But, just what would that be?

 

[DanR]

Could it be "likely" that two Tach's are bad? They worked before being removed and I have paid special attention not to drop or handle them rough.

How to test them? If they don't work for some reason, Guess it best to send them to one of our "Specialty" folks? Huh?

Any suggestions in that regard?

 

[Tom H]

Both the wire to the tach spade and the white wire looping thru the tach should be connected to term 2 of teh ignition switch.

I doubt both tachs are dead- probably off by 50% , but not dead.

Biggest, most likely, issue is the metal U clip goes outside the pastic wire holder. You MUST have that streel clip and it must make contact at both tips with the mating part protruding out from the case.

Do you have the metal clip in place? Is it making contact at both tips?

Tom

P.S I see your PM. E-mail is much better. I LIVE on e-mail. PMs have little storage space

PPS. Is the tach case grounded? Easy way to check- Does the lamp light up?

 

[DanR]

Both the wire to the tach spade and the white wire looping thru the tach should be connected to term 2 of teh ignition switch...... THEY ARE

I doubt both tachs are dead- probably off by 50% , but not dead.

Biggest, most likely, issue is the metal U clip goes outside the pastic wire holder. You MUST have that streel clip and it must make contact at both tips with the mating part protruding out from the case..... I've tested and re tested (by eye)

Do you have the metal clip in place?.... Yes

Is it making contact at both tips?.... Yes


PPS. Is the tach case grounded? Easy way to check- Does the lamp light up?

.....Yes! Grounded! .....Yes! The light comes on.

After checking and re-checking and checking again, no reading....

 

[Tom H]

Hmmmm, And if the white wire that loops thru the tach is disconnected from Term #2 , does the car still run?

Tom

 

[Tom H]

For anyone following this thread, Dan and I have spoken by phone, When he disconnected the white wire that loops thru the tach, the car still ran- NOT GOOD. That means that NOT all the current to the coil was going thru the wire that loops thru the tach. That would prevent the tach from sensing the curent pulses. He is using Pete's wiring , which has a seperate wire (Pink) to power the coil. Dan then removed the pink wire from the coil and we verified that now all the coil current was going thru the loop on the tach. Unfortunately the tach still reads zero. He's sending me the tach for eval/ repair.

Tom

 

[scotdunc]

This thread came at an opportune moment, as apart from sorting my O/D wiring (Many thanks Tom, works a treat now). The only other thing thats never worked on my SV is the tacho ... so prompted by this thread, I thought I would have a closer look at my wiring, and all seems to be hooked up correctly.... with the exception of NO metal 'U' clip holding the little plastic cap to the back of the tacho.
So I guess thats why mine doesn't work, but where to get the little clip!!! Or can I try and make one up with thin tin!!! And also, I guess its a case of trial and error to determine which way round the 'loop' fits onto the tacho.

Toot toot all

 

[Tom H]

Yes, you can make a U clip from a "tin" can. But be sure it is a steel can. Test it with a magnet. If the magnet sticks, the metal is steel. Try for as thick a piece as possible. It seems that can tops are thicker. I made one from the top of a 5# coffee can. Just cut it to fit around the plastic piece, with rounded tips protruding well past the plastic so they make good contact with the inner half. Do not use galvanized steel. The galvanic (zinc) coating is too thick and makes for too large a gap in the ferrous core path.

Tom

 

[DanR]

scotdunc

Just sent you a PM on the clip.

 

[DanR]

TO: sunbby
TomH
Pete

First off I say Thanks Much for the help!

Next, sunnby mentioned something about the "direction of the white wire"

I'm not exactly sure what he was saying.... so I removed the Tach from my "Original" SIV Alpine to see if there was something to what I at least thought he said on the "direction" of the wire....

I disconnected the "Pink" Coil wire that is in Pete's Wiring Harness and started the engine .... the Tach was dead! I disconnected the "white looped wire" both ends and swapped the Purple (Tach) and the power lead from the switch to the "Spade" on the Tach....Then tried again. The engined started and the Tach now reads RPM

I then did a test that TomH said earlier and disconnected the power lead to the Spade to see what would happen. The engine stopped.

Re-hooked the wire to the Spade and started the engine .... the Tach again displayed the RPM's Whoopie!!!!

Does it really matter that the white Looped wire has to have the "Correct Direction"? Appears so from this test!

Does or has anyone else had this problem? Sunbby's comment?

 

[scotdunc]

Cheers Tom, I'll get the tin snips out and get something together. Dan replied your message, but Im in the UK!

By the way, is there a way to test a tacho .... while its off the car?

Toot toot all

 

[Tom H]

Dan, Yes the direction of the loop does matter. And it requires a different direction depending on the polarity of the car. I had not understood that at least one of your tachs was from an SIV. But shoulda tried reversing the loop! Nice work Sunnby and Dan. I did not follow 100% what you described in the wiring, but it's clear that you ended up with one current path from Ign switch to the coil and that path loops in the right direction thru the pick up on the rear.

Based on previous experience I would guess that your tach will read about 50% high. A few of 45 year old parts are critical to teh accuracy and almost surely have drifted pretty far from original value, especially the timing capacitor and thermistor. But at least you have it wired correctly now.

Scott , yes it is possible. Just use a 12 V power supply and an accurate signal generator,with a 50 ohm output impedance, that can put out a 30 Hz to 200 Hz square wave with about a 30% ( or lower) duty cycle. Wind about 30 turns of small wire around the Steel U-clip, and connect the ends of that 30 turn loop to the generator ouput. Set the generator to the desired frequency (RPM/30= Gen Freq)

900 RPM = 30 Hz, 1500 RPM = 50Hz, 2400 RPM = 80 Hz, etc.

If you just want to "test" it . Use your car. Connect some test leads from +12 somewhere on the car to the power spade lug and a second lead to connect ground to the case. Disconnect the white lead from the + terminal of the coil and route it thru the U clip on the rear of the tach and reconnect it to the Coil +. ( leave the plastic piece on the wire, right where it is inside the car. It's not needed for a test. Start the car and see if it works.

Tom

 

[DanR]

Tom H & Sunbby

You guys mentioned earlier about updating the Tech Data on the Forum dealing with the TACH.

Now this would be a great time to add or at least clarify the "directions" of the Tach wire.

Don't you think?

Thanks again,