Need Help Trouble Shooting Tach / MSD Problem

[jabb]

I have an MSD 6AL box with a Tach / MSD convertor box.
Everything was working fine until the other day.
Now The Tach does not work.

I have an RPM / Dwell / Volt meter to do my testing.

Here is waht I did.

Check Black and Purple wire at the tach an I have no Signal.

Check the Tach lead coming out of the MSD 6Al box and I can read a signal. This connection goes into the Tach convertor box.

If I read the wire going to the Tach coming out of the TAch convertor box I get no Signal.

Here is my issue, maybe the Dwell / RPM meter I have can not
read the signal coming out of the convertor box. So I still do not know for sure if the MSD convertor box is bad or the Tach went bad.

What I need is for someone with an RPM / Dwell meter analog gauge to read the TACH signal coming out of the MSD convertor box and see if you get a signal.

If possible pop the TACh an see if you can read a signal off the Black/purple wire.

My hestitation is that the meter can not read the signal after its converted but I have no way of knowing this for sure any help or troubleshooting you can do for me will be greatly appreciated.

ThanK You

[Early_S_Man]

Joe,

Put a test lamp on the Black/Violet wire at the tach ... with the other lead of the test lamp connected to +12 Volts, then see if your tach/dwell meter can see the signal.

[jabb]

Hi Warren:

Let me see If I got this.... At the Tach / Dash wire insert
the point of me test lamp an hook the lead on the test lamp to a
+12 .... Than at the other end of the wire hookup the Meter ?

What is this testing the Wire ?
I am undersatnding this correctly ?

Thank You

[Early_S_Man]

Joe,

1. If I am assuming correctly, your dwell meter is a Sunpro/Acton CP 7676, or equivalent, and connections at the car's tach tach are left as normal during testing, i.e., not disconnected!

2. At the engine compartment ... everything left just as 'normal' ... however it is running now.

3. At the tach ... TD lead is still connected to Black/Violet lead from MSD tach adapter, and also is connected to positive (+) input lead of dwell tach, and negative (-) input lead of dwell tach is connected to ground.

4. At the TD lead of tach, or at + lead of dwell tach ... one side of test lamp is connected ... with other side or probe connected to +12 Volts.

5. An alternative [if above method doesn't give a valid reading] connection for the dwell tach is to connect '+' lead to +12 Volts, and the '-' lead to TD lead at car's tach.

The purpose of this test is to see if a valid switched ground signal is coming from the MSD tach adapter ... and to see if the 'pullup' resistance load of the test lamp allows the dwell tach to get a valid signal and good reading. An additional possibility is that car's tach may start working ... if the internal pullup resistor is defective or has a broken circuit or bad solder joint.

A conventional oscilloscope connected the same [in parallel] as the dwell tach would also give you a useful test of the MSD tach adapter.

[jabb]

Warren

I did what you said.... What I got is a dim light on the test
light at the BLK/Purple Wire... But as I add throttle the light
gets brighter, so my assumption here is the
MSD and MSD Tach convertor are working properly,
and the Tach is the Culprit.

I however do not read any RPMS on the Meter during this test.

Thanks