Help me understand what this is

[Jeff Erwin]

1971 Dodge Superbee 440x6. I've owned it about 8 months, now upgrading the dash to add a tach. Not the original engine. MSD red-cap distributor, looks brand new inside. And this thing:

Its a Wells something. On the back:

And no other identifying marks.

The plug looks like this:

Question is: What is it and how can I hook up an original Rally Dash tachometer to it without blowing something up?

The MSD ignition modules seem to have a 'tach out' connection, should I replace this with a MSD ignition box?

 

[toolmanmike]

The Wells unit is a electronic ignition module.

 

[Jeff Erwin]

The Wells unit is a electronic ignition module.

I kinda figured that, more interested in some specs that might tell me what the connector wires are.

 

[BeepBeepRR]

You hook up the factory tach wire to the negative post on the coil. Pretty sure all of the ECU's wire the same. Here is a drawing. Most likely the green wire is not used. Didnt see the distributor you were using. Was not scrolled down far enough.
Is that an MSD RTR distributor?

 

[toolmanmike]

I kinda figured that, more interested in some specs that might tell me what the connector wires are.

Sorry I just read the headlines and looked at the pictures. I didn't read the fine print.

 

[Jeff Erwin]

You hook up the factory tach wire to the negative post on the coil. Pretty sure all of the ECU's wire the same. Here is a drawing. Most likely the green wire is not used. Didnt see the distributor you were using. Was not scrolled down far enough.
Is that an MSD RTR distributor?
View attachment 1157193

Pretty sure this is what I was looking for! Thanks! I had been reading about hooking factory tachs to an electronic ignition system and frying them because of the increased amperage, don't want to do that. This appears to be a factory spec part so the tach should hook to the negative side without creating a mushroom cloud.

 

[Bee1971]

Screw the tach

LOL

Let’s see some pictures of the car and more info

Thanx Scott

 

[Jeff Erwin]

1971 Superbee.

After detailing:

Before detailing:

 

[Nacho-RT74]

You hook up the factory tach wire to the negative post on the coil. Pretty sure all of the ECU's wire the same. Here is a drawing. Most likely the green wire is not used. Didnt see the distributor you were using. Was not scrolled down far enough.
Is that an MSD RTR distributor?
View attachment 1157193

Becarefull with this diagram, since it shows the ballast bypass being feeded from starter relay. This is true just on lates 70s cars and laters with the specific starter relay for that, but not at least up to 74.

 

[BeepBeepRR]

Becarefull with this diagram, since it shows the ballast bypass being feeded from starter relay. This is true just on lates 70s cars and laters with the specific starter relay for that, but not at least up to 74.

Right on earlier cars that Yellow shown would not be yellow I believe it would be a brown wire. Up to 70 I think. Not sure beyond that.

 

[Nacho-RT74]

not just because it shows yellow color, but also is noted like running to the Starter relay provision for that

which it was used since 75 or 76... or something like that LOL

An all years the wire section running up to ballast from ign switch fro the Ign2 stage is brown. Then the wire from ballast up to coil is blue up to 69 and become brown on 70 to make diff over the blue wire running now to the second alt field which is blue.

 

[Jeff Erwin]

You hook up the factory tach wire to the negative post on the coil. Pretty sure all of the ECU's wire the same. Here is a drawing. Most likely the green wire is not used. Didnt see the distributor you were using. Was not scrolled down far enough.
Is that an MSD RTR distributor?
View attachment 1157193

So to test this tach out of the dash can I just hook up the negative side of the coil and a power source?

 

[Bee1971]

You need a ground also

Are you running an factory original 7,000 RPM Tach or one of the Reproduction 8,000 RPM Tachs

 

[Bee1971]

Pretty sure this is what I was looking for! Thanks! I had been reading about hooking factory tachs to an electronic ignition system and frying them because of the increased amperage, don't want to do that. This appears to be a factory spec part so the tach should hook to the negative side without creating a mushroom cloud.

Factory Tach where installed / option on the 1971 - 1974 B Bodies
1972-1974 had electronic ignition from the factory so

 

[Jeff Erwin]

You need a ground also

Are you running an factory original 7,000 RPM Tach or one of the Reproduction 8,000 RPM Tachs

Factory original. Does that matter?

 

[Bee1971]

The bigger question is your MSD Distributor

From what I see it’s just your typical magnetic trigger on / off for an external ignition module
Which is that Wells unit like mentioned , just an aftermarket for the Mopar ECU Ignition Module


You don’t have any extra wires going to your battery ?

Don’t laugh - I have seen guys get pretty good at hiding MSD Ignition Boxes where you can’t tell unless your looking at the extra wiring coming off the battery

Under the battery
On the frame
Under the dash

Then they will keep the factory stuff in place for that factory appearance look

I would assume that’s not the case and you would bee fine running a factory tachometer off the negative side of the coil

What coil are you running and is a ballast resistor in place ?

 

[Jeff Erwin]

The bigger question is your MSD Distributor

From what I see it’s just your typical magnetic trigger on / off for an external ignition module
Which is that Wells unit like mentioned , just an aftermarket for the Mopar ECU Ignition Module


You don’t have any extra wires going to your battery ?

Don’t laugh - I have seen guys get pretty good at hiding MSD Ignition Boxes where you can’t tell unless your looking at the extra wiring coming off the battery

Under the battery
On the frame
Under the dash

Then they will keep the factory stuff in place for that factory appearance look

I would assume that’s not the case and you would bee fine running a factory tachometer off the negative side of the coil

What coil are you running and is a ballast resistor in place ?

MSD coil and the ballast resistor is in place. The wires from the ignition box actually connect to things, so likely not a fake.

 

[Bee1971]

Factory original. Does that matter?

The reproduction 8,000 Tachs are designed for aftermarket ignition systems if needed

Anyways read my last post

 

[Bee1971]

They make a reproduction factory wiring harness for your tachometer

The negative coil wire will run directly thru your bulkhead connector on 1971

Nacho can give you the exact location or number

 

[Bee1971]

1971 B Body

https://www.megapartsusa.com/proddetail.php?prod=104-TWH103