OT: Chevy 250 External Coil-tach

Courtland1949 · Nov 9, 2019

Where do I attach a hand-held tachometer to a HEI-ignition system with an "external" coil on a 1976 C10 inline 6-banger?? Thx

UncleTom · Nov 9, 2019

crank shaft? why would you want to.

Courtland1949 · Nov 9, 2019

Idle and timing....

JimmyDean · Nov 9, 2019

(quoted from post at 21:25:22 11/09/19) Where do I attach a hand-held tachometer to a HEI-ignition system with an "external" coil on a 1976 C10 inline 6-banger?? Thx

I would have to say the one connection would go on the neg. side of the coil and the other to ground.

TGP · Nov 9, 2019

Attach it to the small wire from the coil to dist.
Not the Ign. wire.

Should work. Also might be marked Tach. on the connector
Or a Tach. lead unused hanging off the harness.

Tom

guido · Nov 9, 2019

Hello Courtland,

TGP Is correct, you may also find the coil marked with a plus side, that is the ignition side, tack pick up goes on the other side of the coil,Other tack wird goes to ground,

Guido.

Bob · Nov 9, 2019

(quoted from post at 20:25:22 11/09/19) Where do I attach a hand-held tachometer to a HEI-ignition system with an "external" coil on a 1976 C10 inline 6-banger?? Thx

You have gotten good advice as to where to connect the tach.

However (in my humble experience), if it's just a generic tach (and not specifically made for HEI use) there'll be a wide margin of disagreement between the hand-held electronic tach reading and the actual engine speed.

Courtland1949 · Nov 10, 2019

TY all for your advise. Appreciate it.

Mike M · Nov 10, 2019

Does your tach have different setting like 4 cyl. 8 cyl 6 cyl ? The one I have does and then for 4 or 8 you have to divide or multiply by 2 IIRC ? been years since I ran it. Used it on 2 cyl. too just had to calculate it correctly.

David G · Nov 10, 2019

I thought HEI had integral coil, there should be a pin to attach to for external tach.

David G · Nov 10, 2019

OK, from what I can remember there are two wires coming out of distributor, the red is power in, the green is tach out.

Others can confirm/deny.

Bob · Nov 10, 2019

(quoted from post at 11:35:48 11/10/19) OK, from what I can remember there are two wires coming out of distributor, the red is power in, the green is tach out.

Others can confirm/deny.

He stated he has the HEI with an EXTERNAL coil.
Yes, that's how GM made the L6 HEI in 1976.

There are two wires between the distributor and the coil primary, RED is "Power" from the ignition switch, the other wire (I believe) is white, and this is the pulsed wire where one would connect a tach.

Some even have a short pigtail with an unused connector already there for the purpose.

David G · Nov 10, 2019

Thanks

Courtland1949 · Nov 10, 2019

There are 2-wires. One blach, one red. Do I nees a bare wire connection??

Bob · Nov 10, 2019

(quoted from post at 19:28:24 11/10/19) There are 2-wires. One blach, one red. Do I nees a bare wire connection??

Are referring to the color of the wires at the coil, or the test leads on your hand-held tach?

As to making a temporary connection for testing, years ago I had a hand-held tach that came with a little "hair pin" like would be used in a small clevis pin.

With the engine "off" you inserted the leg of the hairpin next to the push-on terminal in a plastic connector body, then clipped the alligator clip on the test lead to the hairpin.

(IIRC, the connection at the coil is not a sealed connector, so there's no need to piece a wire for a temporary test connector.)

Just be careful not to let it short to ground.

Courtland1949 · Nov 10, 2019

Referring to Color of wires running from dist to coil. This coil is mounted to the engine block. Separate
from dist. And it's just not obvious to me where to get a pickup lead for a hand held tach..?? Hum.

Thx

Bob · Nov 10, 2019

(quoted from post at 20:47:52 11/10/19) Referring to Color of wires running from dist to coil. This coil is mounted to the engine block. Separate
from dist. And it's just not obvious to me where to get a pickup lead for a hand held tach..?? Hum.

Thx

What make/model/type of tach are you attempting to use?

Courtland1949 · Nov 10, 2019

Dixon. 2-wire aligator clips.

Photo of ign attached.

Courtland1949 · Nov 10, 2019

Tach

Bob · Nov 10, 2019

Clip black TEST LEAD to a good ground.

At the coil, connect the red TEST LEAD to a hairpin, as I posted, or a thin nail or other makeshift test probe inserted in the connector at the coil so it contacts the end terminal on the non-red wire from the distributor.

There's actually 4 terminals on the coil, the ones closest together are "common" with each other.

Courtland1949 · Nov 10, 2019

I pulled the small cover on top of the coil and don't recall seeing connectors like that ..?

Courtland1949 · Nov 11, 2019

After a closer look, as in hopping in the engine bay, I found it.....

OT: Chevy 250 External Coil-tach

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