Chevy Nova Forum banner
1 - 13 of 13 Posts

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #1 ·
Does anyone know if I might have a problem running my wire from the (-) of the coil through a bulkhead
connector to the Tach? I've got a connector not being used and would like to hide that wire inside the
harness if I can. ????
 

·
Moderator
Joined
·
6,748 Posts
Gotta do the research.

I bought a 74 Spirit of America Nova and it did not have the optional console gauges (oil, water, gas, ammeter) and after looking at factory wiring diagrams I figured out what pin in the bulkhead connector was used to pass through the ignition coils negative to trigger the indash tachometer and then after getting the proper terminals for the bulkhead connector and at the coil, I added things and then loomed things up to make the conversion hardly undetectable.

For your info, the flexible circuit board is the same between a gas gauge setup and a tach setup. It's just where the wire off of the instrument panel goes (either to the gas sender or to the coils negative terminal).

I also modified the interior harness to support the water and gas circuit but then instead of keeping an ammeter gauge circuit I modified things to use a newer console volt gauge.

Recently I bought some of the bulkhead connectors for the 69 and up bulkhead connectors as well as some bulkhead connectors for the 67 and older models.

You never know when you might need that kind of stuff just like weatherpack connectors.

Jim
 

·
Registered
Joined
·
3,912 Posts
Does anyone know if I might have a problem running my wire from the (-) of the coil through a bulkhead
connector to the Tach? I've got a connector not being used and would like to hide that wire inside the
harness if I can. ????

I would not do that.

When you say the "(-)" lead makes me think you might use some help from a stereo installer. They are actually very knowledgeable about just about every car out there And with-in that there is the byproduct of learning about every aspect of many car electrical systems.

Other than that yup, that is in fact how you wire a tach up. When going through the bulkhead make sure to have a nice grommet in there, live wire.

I like what you are doing JR
 

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #4 ·
After rewiring the bulkhead connector to accept the extra wires required for a Wiper motor/Water pump
I ended up with a spare opening. Since I added those wires to my harness to accept the W/W wires I got
to thinking I could also include the tach wire. My main concern was introducing a pulse into the surrounding
wiring because that wire would be running inside of the Engine Harness to the Bulkhead connector.

Jim, it seems you've had no problem doing what I want to do so I'll use that opening. I guess the only thing
that might be affected would be some possibility of a pulse being introduced into the radio wiring but if that
happens then adding a capacitor to radio power wiring might stop that. Just trying to think ahead.

Any other suggestions or experiences?
 

·
Registered
Joined
·
822 Posts
There should be no problem running that wire through the bulkhead conn to the tach. As you suggested, you can always add a filter if you do get a little static on the radio. I don't believe the ignition noise commonly heard in the radio is from that tach signal wire. It's usually from the coil or secondary ignition (spark plug) wires. Let us know how it goes.
 

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #6 ·
OK guys, it's going on that pin. I appreciate the advice. I'm going to be tracing all my harness wires to make sure they are
where they should be. As far as I know this is the last of the changes to the Dash harness. My new headlight harness is on
the way so I'll be starting on it soon to add relays for the headlights and modifying the diagram. Thanks to all you guys that
continue to help me. Slow but sure, that's me! (y)
 

·
Moderator
Joined
·
6,748 Posts
Here is an old drawing I have of a 1974 bulkhead connector and the tachometer signal wire is circuit number 121 between circuit 6 which is the purple wire to the starter solenoid and circuit 141 which is a Brown-White that goes to the idle solenoid. Again, this is for a 74 so on other years this Brown-White may not be present

Back when I did mine I got a brown wire off of a donor harness to make my conversion hard to detect and now days you can buy the bulkhead terminals and make up your own harness setup.

2012-2-18 (1) Bulkhead Connector (A) Engine Side.jpg

I really doubt one would have any noise issues as this tach signal wire was loomed in with other wires under the hood and under the dash and todays electronics (mostly) are protected a lot better to reject unwanted noise.

Found another photo of where I added the Brown wire for the tach:

1974 Nova Fuse Block Apart (3) Added Tachometer Signal Wire.JPG


Jim
 

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #8 ·
Thanks Jim. That is interesting for sure. I like the way you have "uses" charted as to the connectors. I might borrow
your idea and do the same for my wiring. It'll make referencing a lot simpler instead of having to trace all the lines
to and from their connectors. I'm glad you sent that.

I do have some of the bulkhead terminals and a crimper. I'm not so concerned about wire color as I haven't been able
to find any reference to the tach wire specs for the '65. Since my diagram is going to be somewhat specific for my Nova
I thought I'd just use a long wire out of my old harness. I found a long brown wire that extends the full length of the old
harness so brown it is. (y)

Looks like this will work with no problems. It's always good to have other opinions and I do value you guys to steer me
in the right direction.
Sam
 

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #10 ·
As a matter of fact I do have one of those harnesses already. I found it last night after rummaging threw some more
of my boxes. The Tach wires are pink and brown. Now if I only knew which went where on my tach, I'd be set. See
my other conservation. I'm going to go ahead and wire the brown wire in my harness. If I don't figure out the wiring
of my tach then I'm set to buy another tach that will accept the round contacts in this harness.

DSCN0173.JPG
 

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #11 ·
I'm back to working on the tach wiring. I did finally get the brown wire from the coil down through the fuse panel and over to where
the tach will be positioned. Now for another question. The original harness shown in the photo above has a pink wire which has to
be connect to a 12v switched source (I would think) . Any suggestion?
 

·
Premium Member
1965 2door HT Helena, GA 31037
Joined
·
1,746 Posts
Discussion Starter · #13 ·
Thanks, I did see that. My problem was that I was trying to find a "Pink" switched source to tie into since that was
the IGN switched source from the BAT and I didn't see one that would work for me. Now I see that the pink wire
wasn't actually intended to be the source for the TACH. Instead it looks like the brown ACC wire from the ignition
switch is the source through the fuse panel to that particular pin shown in the drawing. I checked my ignition
switch and found that the Brown wires and the pink wire are both active when the ignition switch is in the ON position.
OK, another bit of knowledge found thanks to you. Sam

PS, Please stick with me as I'm almost 74 and the old brain just doesn't function like it used too.
 
1 - 13 of 13 Posts
Top