Can't Get Auto Meter Tach to Work

[RPM 1,190]

On my 69 Mach One 351W with stock ignition, points and condensor. The Ultra Lite series tach is in a 6 gauge bezel and the other gauges work. 

 

I installed it as per the instructions:

 

12v fused power, which it has,

Source feed wire from the negative coil post, 

A good ground, which servers as the ground for other working parts on the car.

 

All of the wires have continuity and power when the engine is running.

The engine starts right up, and runs smooth.

All of the connections, wires and routing have been checked 6 plus times.

I ran additional separate wires from the harness for the 12v power, coil wire and ground w/o success.

I hooked up a break in stand tach I had using separate wiring w/o success.

I bought a 3rd tach in case the first 2 were bad, it didn't work either.

Bought and tried a second coil, no luck

Every connection and wire crimp has been checked several times.

 

I switched the coil wire from the negative post to the positive post on my break in stand tach and it worked properly.

I hooked up the Auto Meter tach to the positive coil post, no tach needle movement.

I called Auto Meter who said the wire connects to the negative coil post. If connected to the positive it will burn up the tach.

 

Everything I've read or heard has the coil negative post used for the tach. Until this experience I've always thought tach wiring was a close second to hooking up the battery for ease of installation on these cars. I'm beginning to think I really don't need a tach in the car. 

 

Has anyone had a similar experience or ideas? I'm open to any and all suggestions, other than what I've already tried many times. 

 

Thanks.

[Mach1 Driver 560]

White to dash lights positive

Red to ignition switch C and fused

Black to ground

Green to coil negative- that's the points side

Switches or wire loops for number of cylinders

 

I think you may have covered all those bases

[RPM 1,190]

I think you may have covered all those bases

 

Ya, several times a day for 2 days. Kinda wish I hadn't so I might have something to check. If I don't get any new ideas I'll remove the tach and check it on my brother's 69 Mach, 2 hours away. 

[Midlife 814]

I've been working with RPM with this problem over the past week, and I'm stumped!  It should work.  What's strange is a separate aftermarket tach works only when the signal comes from the + side of the coil, which makes no sense.

 

It's gotta be something really really simple, worthy of a forehead dope-slap, but what, I don't know. 

[larryc94 38]

On my 69 Mach One 351W with stock ignition, points and condensor. The Ultra Lite series tach is in a 6 gauge bezel and the other gauges work. 

 

I installed it as per the instructions:

 

12v fused power, which it has,

Source feed wire from the negative coil post, 

A good ground, which servers as the ground for other working parts on the car.

 

All of the wires have continuity and power when the engine is running.

The engine starts right up, and runs smooth.

All of the connections, wires and routing have been checked 6 plus times.

I ran additional separate wires from the harness for the 12v power, coil wire and ground w/o success.

I hooked up a break in stand tach I had using separate wiring w/o success.

I bought a 3rd tach in case the first 2 were bad, it didn't work either.

Bought and tried a second coil, no luck

Every connection and wire crimp has been checked several times.

 

I switched the coil wire from the negative post to the positive post on my break in stand tach and it worked properly.

I hooked up the Auto Meter tach to the positive coil post, no tach needle movement.

I called Auto Meter who said the wire connects to the negative coil post. If connected to the positive it will burn up the tach.

 

Everything I've read or heard has the coil negative post used for the tach. Until this experience I've always thought tach wiring was a close second to hooking up the battery for ease of installation on these cars. I'm beginning to think I really don't need a tach in the car. 

 

Has anyone had a similar experience or ideas? I'm open to any and all suggestions, other than what I've already tried many times. 

 

Thanks.

 

 

White to dash lights positive

Red to ignition switch C and fused

Black to ground

Green to coil negative- that's the points side

Switches or wire loops for number of cylinders

 

I think you may have covered all those bases

I'm confused on your terminology. What color from the tach do you have as the "source feed wire"

 

Larry

[RPM 1,190]

Larry if you're asking me, the wire which connects to the coil is red/black but it's not relevant because my gauge cluster wiring harness is custom to my car. 

[larryc94 38]

If you hook up the tach under the hood directly it still doesn't work?

 

Larry

[Rsmach1 71]

Check the tachs ground wire. Trace it from the back of the tach too ground. Also try grounding it separately all by itself.

[TheRktmn 15]

Check that the coil - post is going to the distributor. I have seen quite a few that had the + post going to the distributor.

[danno 128]

I am trying to understand the break in stand tach. Is this a separate tach, not connected to anything on the car?  Typically used for engine evaluation?  I thought these hooked up to a spark plug wire, but maybe the one you have is different?

 

The coil has a + wire to the hot side, usually the ignition switch.  It has the - side that goes to the points.   I think these can be reversed and the car will work fine. Bob (above) mentioned this.  But you mentioned you hooked up your break in tach to the + terminal and it worked fine.  This tells me that you maybe have the coil wired backwards.   Perhaps you have the + wire going to the points?

 

If you are using the standard wires, then you have a resistance wire from the ignition switch to the coil. It could be possible the use of a resistance wire will not work with your ultra lite tach.  You can try shorting out the resistance wire when the car is running to see if the tach will then work.  You can short the resistance wire without hurting anything if only done for a few seconds. Doing so for a long period of time will heat up the coil and eventually it will fail.  To short this out, you need a separate wire from the + battery terminal to the coil wire that goes to your ignition switch.  Again, verify the + terminal on your coil goes to your ignition switch.   With the resistance wire temporarily shorted, does the tach work then?

 

Midlife, does this make sense as a possibility?

[RPM 1,190]

The break in tach is a normal tach, just a different one. I've been helping my daughter move and will check the routing to/from coil tonight.

Thanks guys.

[69NC 21]

Bob,

 

A few questions.

1.  if you hook up the break in tach, it's under the hood? where as the auto meter tach has wires running to the dash area?
    
2. Do you have the filter cap in place? if it is missing, or bad there could be noise that is confusing the tach (Not as likely as you have no movement, and not a bouncing tach)
   
   1. http://image.cpsimg.com/sites/carparts-mc/assets/classroom/images/ignitiondiagram.gif
       
3. if you have a test light, or a volt/ohm meter  you check that you have tach wired in correct (Like is mentioned above)
   1. if you can get the tach to work under the hood, then check that the wires running to the dash don't have any breaks/opens
   2. An easy way to check the pulses is to unplug the high tension lead to the distributor cap and and ground it.  Then hook up the volt meter set to AC, between ground and the neg terminal on the coil.  when you crank the engine you should see some voltage reading (this is caused as the points open a close grounding our the coil).  If you move the voltage probe from the neg side of the coil to the pos side, you should not see any voltage as it should remain at 12 V DC (remember the volt meter is on AC, so it is expecting to see a cycle in the voltage)
   3. A test light will flash on the neg side, and be on steady on the pos side
       
4. Do you have a pertonix ignitor?  I have seen them cause problem with some Tachs

 

If you want more help, you can contact me directly.  PM for info.

 

This is completely aside, and please don't take this wrong, but I see a bit irony in that you have the handle of RPM, and you have a tach problem :D

[RPM 1,190]

I'm confused on your terminology. What color from the tach do you have as the "source feed wire"

 

Larry

The signal wire. The one that has the tach show the particular rpm.

[RPM 1,190]

If you hook up the tach under the hood directly it still doesn't work?

 

Larry

The Auto Meter tach in the gauge bezel? If so, I haven't taken it out of the bezel

[RPM 1,190]

Check the tachs ground wire. Trace it from the back of the tach too ground. Also try grounding it separately all by itself.

I've done this multiple times.

[RPM 1,190]

Check that the coil - post is going to the distributor. I have seen quite a few that had the + post going to the distributor.

Uh oh. I did have the distributor/points wire going to the + coil post. I switched it to the - post without success using the harness wiring, then ran separate dedicated wires w/o success. 

[RPM 1,190]

I am trying to understand the break in stand tach. Is this a separate tach, not connected to anything on the car?  Typically used for engine evaluation?  I thought these hooked up to a spark plug wire, but maybe the one you have is different?

 

It is a standard tach which gets wired as any I've ever seen. It is not an evaluation piece of equipment

 

The coil has a + wire to the hot side, usually the ignition switch.  It has the - side that goes to the points.   I think these can be reversed and the car will work fine. Bob (above) mentioned this.  But you mentioned you hooked up your break in tach to the + terminal and it worked fine.  This tells me that you maybe have the coil wired backwards.   Perhaps you have the + wire going to the points?

 

This is spot on. But I have corrected it.

 

If you are using the standard wires, then you have a resistance wire from the ignition switch to the coil. It could be possible the use of a resistance wire will not work with your ultra lite tach.  You can try shorting out the resistance wire when the car is running to see if the tach will then work.  You can short the resistance wire without hurting anything if only done for a few seconds. Doing so for a long period of time will heat up the coil and eventually it will fail.  To short this out, you need a separate wire from the + battery terminal to the coil wire that goes to your ignition switch.  Again, verify the + terminal on your coil goes to your ignition switch.   With the resistance wire temporarily shorted, does the tach work then?

 

I'll wait for Midlife to reply to this.

 

Midlife, does this make sense as a possibility?

[RPM 1,190]

Bob,

 

A few questions.

1.  if you hook up the break in tach, it's under the hood? where as the auto meter tach has wires running to the dash area?

    

2. Do you have the filter cap in place? if it is missing, or bad there could be noise that is confusing the tach (Not as likely as you have no movement, and not a bouncing tach)
   1. http://image.cpsimg.com/sites/carparts-mc/assets/classroom/images/ignitiondiagram.gif

       

3. if you have a test light, or a volt/ohm meter  you check that you have tach wired in correct (Like is mentioned above)
   1. if you can get the tach to work under the hood, then check that the wires running to the dash don't have any breaks/opens
   2. An easy way to check the pulses is to unplug the high tension lead to the distributor cap and and ground it.  Then hook up the volt meter set to AC, between ground and the neg terminal on the coil.  when you crank the engine you should see some voltage reading (this is caused as the points open a close grounding our the coil).  If you move the voltage probe from the neg side of the coil to the pos side, you should not see any voltage as it should remain at 12 V DC (remember the volt meter is on AC, so it is expecting to see a cycle in the voltage)
   3. A test light will flash on the neg side, and be on steady on the pos side

       

4. Do you have a pertonix ignitor?  I have seen them cause problem with some Tachs

 

If you want more help, you can contact me directly.  PM for info.

 

This is completely aside, and please don't take this wrong, but I see a bit irony in that you have the handle of RPM, and you have a tach problem :D

 

1. if you hook up the break in tach, it's under the hood? where as the auto meter tach has wires running to the dash area?

 

This is correct.

 

2. Do you have the filter cap in place? if it is missing, or bad there could be noise that is confusing the tach (Not as likely as you have no movement, and not a bouncing tach)

1. http://image.cpsimg.com/sites/carparts-mc/assets/classroom/images/ignitiondiagram.gif

I don't understand the filter cap question. The wiring is now as in the linked diagram.

 

3. if you have a test light, or a volt/ohm meter  you check that you have tach wired in correct (Like is mentioned above)

1. if you can get the tach to work under the hood, then check that the wires running to the dash don't have any breaks/opens
2. An easy way to check the pulses is to unplug the high tension lead to the distributor cap and and ground it.  Then hook up the volt meter set to AC, between ground and the neg terminal on the coil.  when you crank the engine you should see some voltage reading (this is caused as the points open a close grounding our the coil).  If you move the voltage probe from the neg side of the coil to the pos side, you should not see any voltage as it should remain at 12 V DC (remember the volt meter is on AC, so it is expecting to see a cycle in the voltage)
3. A test light will flash on the neg side, and be on steady on the pos side.

I will do this hopefully later tonight. But seeing how it's 103* with quite a bit of humidity, I might wait till the morning.

 

4. 

1. Do you have a pertonix ignitor?  I have seen them cause problem with some Tachs

I do not have a Pertonix. Stock point and condenser.

 

If you want more help, you can contact me directly.  PM for info.

 

PM sent.

 

This is completely aside, and please don't take this wrong, but I see a bit irony in that you have the handle of RPM, and you have a tach problem :D

 

Ya, pretty dang ironic eh? This my friend, made me laugh! Take it wrong? Please. We all need a bit of laughter in our day. Might qualify as the quote of the month! Not only is it my screen name, but they are my initials. 

[Rsmach1 71]

Now that was funny, nice catch.

[Midlife 814]

 

I am trying to understand the break in stand tach. Is this a separate tach, not connected to anything on the car?  Typically used for engine evaluation?  I thought these hooked up to a spark plug wire, but maybe the one you have is different?

 

It is a standard tach which gets wired as any I've ever seen. It is not an evaluation piece of equipment

 

The coil has a + wire to the hot side, usually the ignition switch.  It has the - side that goes to the points.   I think these can be reversed and the car will work fine. Bob (above) mentioned this.  But you mentioned you hooked up your break in tach to the + terminal and it worked fine.  This tells me that you maybe have the coil wired backwards.   Perhaps you have the + wire going to the points?

 

This is spot on. But I have corrected it.

 

If you are using the standard wires, then you have a resistance wire from the ignition switch to the coil. It could be possible the use of a resistance wire will not work with your ultra lite tach.  You can try shorting out the resistance wire when the car is running to see if the tach will then work.  You can short the resistance wire without hurting anything if only done for a few seconds. Doing so for a long period of time will heat up the coil and eventually it will fail.  To short this out, you need a separate wire from the + battery terminal to the coil wire that goes to your ignition switch.  Again, verify the + terminal on your coil goes to your ignition switch.   With the resistance wire temporarily shorted, does the tach work then?

 

I'll wait for Midlife to reply to this.

 

Midlife, does this make sense as a possibility?

Before you do anything more, hook up your test stand tach correctly to the negative coil terminal, now that you've found the original coil wiring was wrong.  Does it now work?  If yes, that's good.

 

My guess is that for all this time, you've been running your autometer dash tach connected to the positive side of the coil and probably burned it up.  If your test stand tach works, but the autometer doesn't, use the wiring through the dash to hook up the test stand tach inside the car.  Still works?  If so and the autometer doesn't, I would highly suspect the autometer tach is bad.

 

No need to bypass the resistor wire just yet...

[Midlife 814]

By the way, you deserve the Dope Slap I've discussed before for reversing the coil leads to the distributor.  *G*

[RPM 1,190]

IT'S ALIVE! Details to follow. Thanks guys, you're the best!

[69NC 21]

IT'S ALIVE! Details to follow. Thanks guys, you're the best!

 

Glad you got it working!  Can't wait to hear what the issue was.

[RPM 1,190]

Well, my heavy handed son who needs to learn the definition of the word finesse, pulled the 12v power wire from its connection. I checked the wires and they were fine for the first hundred disconnects we made while troubleshooting the tach. After it was pulled loose it gave intermittent continuity readings. The fact that "someone" didn't wire the coil correctly surely didn't help.

 

As predicted it was a simple fix, and I'll take that smack upside my head. DOH! Thanks all for your help.

[danno 128]

You are lucky we don't make you pay  for this advise. But then ( to be fair) we would pay you when we give bad advise. As I provide too much bad advise, we better stick to no charge in both directions. 

 

Now we have our RPMs...