Upgrading the electrical in my '72 - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

 7Likes
  • 1 Post By Kirk's67SS
  • 2 Post By lucifershammer
  • 1 Post By Jim Streib
  • 2 Post By Dean
  • 1 Post By lucifershammer
 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 15 (permalink) Old Jun 28th, 20, 8:07 AM Thread Starter
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,644
Upgrading the electrical in my '72

Well, since I've got the car torn apart right now putting the engine in, I was going to address a minor upgrade of the electrical system and wanted to get opinions to see if I should/should not.

The way the '72 is wired from the factory is that there is a positive battery cable going from the battery to the starter. From the same starter post, there is a fusible link connected to a 10 gauge wire which goes to the horn relay. On the alternator, there is a 10 gauge wire that goes from the charging post to the horn relay.

The current stock charging circuit goes alternator->horn relay->battery (via starter 10 gauge & fusible link to large battery cable) and stock power circuit goes battery->horn relay (via starter 10 gauge & fusible link to larger battery cable.)

The fusible link at the starter protects the car from a short and will blow the fusible link at the starter and completely cut off the battery from the rest of the car.

Since I've added a larger alternator and a few other goodies, I wanted to update those 10 gauge wires to 8 gauge wires.

I also was considering moving the fusible link and wire connected to the horn relay from the starter stud up to a stud on the positive battery. You get the exact same wiring flow (alternator->horn relay->battery for charging, battery->horn relay for power), except the fusible link is now at the battery instead of at the starter and is much more accessible should there be an issue, and also I can keep yet another wire away from the exhaust.

Any opinions on that (yay or nay?)

1972 Chevelle, MJ 467, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
lucifershammer is offline  
Sponsored Links
Advertisement
 
post #2 of 15 (permalink) Old Jun 28th, 20, 10:02 AM
Senior Tech Team
Greg.
 
Join Date: Apr 2011
Location: Ottawa, On, Canada
Posts: 5,507
Garage
Re: Upgrading the electrical in my '72

I put one on my Neg. Post on the Battery in the Trunk of car

PICO Fuse Holder # REG 980211
PICO 500amp Fuse # REG 981911
NAPA Battery Cable Terminal # GRO 829595 for Quick Disconnect

Will try and get a Pic and post it


lucifershammer likes this.

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Kirk's67SS is online now  
post #3 of 15 (permalink) Old Jun 28th, 20, 11:26 AM
Tech Team
Troy
 
Join Date: Jun 2015
Location: San Jose, CA.
Posts: 840
Re: Upgrading the electrical in my '72

There a site called Madd electric with some great information on updating the electrical system on these older cars.

Moving the charge wire similar to your thinking is one of those steps, including keeping the fusible link.

Another good step is adding relays for the headlights.

Give Madd electric a look.

Sent from my SM-T720 using Tapatalk

66 CHEVELLE
senna is offline  
 
post #4 of 15 (permalink) Old Jun 28th, 20, 11:28 AM
Senior Tech Team
 
Join Date: Oct 2003
Location: Saint Louis
Posts: 1,310
Re: Upgrading the electrical in my '72

I'm thinking from down at the starter there is a fusible link off of the main battery starter stud and it then connects to a 10 gauge which eventually ends up at the horn relay buss but in that section of wire there is a splice that another 10 gauge connects to and now one end of this additional 10 gauge goes to the alternators output stud and the other end goes to a fusible link which then connects to a terminal on the external voltage regulator.

I can understand moving a protection device like the fusible link to a more accessible location because where it's at if it's anything like on my 73 Nova, the fusible link and connection to the 10 gauge was in a protective steel tube bolted onto the motor and transmission.

With you stating you added a larger alternator and a few other goodies, is how large of an alternator did you put in and where are these other goodies getting power from (Battery post, horn relay buss, fuse block, ?????).

You may have to put in a new wire from the new alternator to the battery post, possibly relocate the voltage sense wire, and maybe move where you are getting power for your new goodies and possible future goodie additions.

Also with the goodie additions, maybe think about upgrading the battery to body ground connection.

Jim

Always working on something:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Jim Streib is offline  
post #5 of 15 (permalink) Old Jun 28th, 20, 12:17 PM
Lifetime Premium Member
Bob
 
Join Date: Mar 2005
Location: Jeannette Pa. near pittsburgh
Posts: 8,893
Re: Upgrading the electrical in my '72

On my 70 SS-454 Wagon, 468/700R4) I went from the pass. side rear of the block, The Cyl. head. ( 69 & up B.B. heads, have two tapped holes, A/C mount when head is on the left side). I ran a ground strap ( from Advance with two 3/8" eyes) from the Cyl. head to the frame. Using the same attachment on the frame I also went with ground strap #2 to the body.
For my pea brain, I like a good ground. I just wanted to eliminate ground issues that old cars will ALWAYS have. So far no ground issues in over 46.000 miles. Both ground straps have 3/8" eyes on each end, and are about 3/8" Dia. cable. In my lifetime I have seen FRIED--Speedometer cables, FRIED Console shifter cables, Head light, tailight issues. My cars are well grounded,Just like I have been for the last couple of months..........
Bob
Why did I do the grounds the way I did?..... Ya Kant See Em....


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
1970 SS LS-5/M-22 El Camino- Org. Owner-AACA 2016-Senior Grand National Winner---MCACN-GOLD-2013
1970 ( FRAUD) SS 468 Station Wagon - Driver.
Robinls5 is online now  
post #6 of 15 (permalink) Old Jun 28th, 20, 1:15 PM Thread Starter
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,644
Re: Upgrading the electrical in my '72

Yup, been there it's a great wealth of information. Already have relays for the headlights.

Quote:
Originally Posted by senna View Post
There a site called Madd electric with some great information on updating the electrical system on these older cars.

Moving the charge wire similar to your thinking is one of those steps, including keeping the fusible link.

Another good step is adding relays for the headlights.

Give Madd electric a look.

Sent from my SM-T720 using Tapatalk
senna and Kirk's67SS like this.

1972 Chevelle, MJ 467, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
lucifershammer is offline  
post #7 of 15 (permalink) Old Jun 28th, 20, 1:19 PM Thread Starter
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,644
Re: Upgrading the electrical in my '72

Wiring in the '72 is different than others years - the horn relay is up on the firewall next to the booster, and everything connects there. There are no crimped splits or such in the harness like other years have.

The red wire from the alternator goes straight to the horn relay. The orange wire with the fusible link from the starter goes to the horn relay. That is the junction where everything is connected.

I've also used that as the junction to draw power to my 2 additional fuse boxes I put in (one in the engine bay, one under the passenger side glove box.)

Alternator is not huge - I think only 78 or 94 amps (can't remember.)

There is no wire from the alternator to the battery post. It goes to the horn relay as mentioned, so yup, I'll be running a few new wires and pulling a few old ones.

Quote:
Originally Posted by Jim Streib View Post
I'm thinking from down at the starter there is a fusible link off of the main battery starter stud and it then connects to a 10 gauge which eventually ends up at the horn relay buss but in that section of wire there is a splice that another 10 gauge connects to and now one end of this additional 10 gauge goes to the alternators output stud and the other end goes to a fusible link which then connects to a terminal on the external voltage regulator.

I can understand moving a protection device like the fusible link to a more accessible location because where it's at if it's anything like on my 73 Nova, the fusible link and connection to the 10 gauge was in a protective steel tube bolted onto the motor and transmission.

With you stating you added a larger alternator and a few other goodies, is how large of an alternator did you put in and where are these other goodies getting power from (Battery post, horn relay buss, fuse block, ?????).

You may have to put in a new wire from the new alternator to the battery post, possibly relocate the voltage sense wire, and maybe move where you are getting power for your new goodies and possible future goodie additions.

Also with the goodie additions, maybe think about upgrading the battery to body ground connection.

Jim

1972 Chevelle, MJ 467, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
lucifershammer is offline  
post #8 of 15 (permalink) Old Jun 28th, 20, 2:00 PM
Senior Tech Team
 
Join Date: Oct 2003
Location: Saint Louis
Posts: 1,310
Re: Upgrading the electrical in my '72

Quote:
Originally Posted by lucifershammer View Post
Wiring in the '72 is different than others years - the horn relay is up on the firewall next to the booster, and everything connects there. There are no crimped splits or such in the harness like other years have.

The red wire from the alternator goes straight to the horn relay. The orange wire with the fusible link from the starter goes to the horn relay. That is the junction where everything is connected.

I've also used that as the junction to draw power to my 2 additional fuse boxes I put in (one in the engine bay, one under the passenger side glove box.)

Alternator is not huge - I think only 78 or 94 amps (can't remember.)

There is no wire from the alternator to the battery post. It goes to the horn relay as mentioned, so yup, I'll be running a few new wires and pulling a few old ones.
I knew they did a change on the Chevelle and other GM models wiring in the early to mid 70's.

I did some searching and it looks like a Russ Green did a LOT of documentation on the wiring on his 72 Chevelle.

Just keep in mind that if you are putting in a 94A alternator that is oversized for what you actually need, run a wire that properly supports it's maximum 94A output and then do the same with the wire going to the battery. Should the alternator fail then power will be coming off of the battery feed line and it needs to be large enough to support the loads.

Jim
lucifershammer likes this.

Always working on something:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Jim Streib is offline  
post #9 of 15 (permalink) Old Jun 28th, 20, 2:08 PM
Lifetime Premium Member
Al
 
Join Date: Apr 2011
Location: SO CAL...Huntington Beach and Rancho Cucamonga
Posts: 5,745
Garage
Re: Upgrading the electrical in my '72

Quote:
Originally Posted by lucifershammer View Post
Wiring in the '72 is different than others years - the horn relay is up on the firewall next to the booster, and everything connects there. There are no crimped splits or such in the harness like other years have.

The red wire from the alternator goes straight to the horn relay. The orange wire with the fusible link from the starter goes to the horn relay. That is the junction where everything is connected.

I've also used that as the junction to draw power to my 2 additional fuse boxes I put in (one in the engine bay, one under the passenger side glove box.)

Alternator is not huge - I think only 78 or 94 amps (can't remember.)

There is no wire from the alternator to the battery post. It goes to the horn relay as mentioned, so yup, I'll be running a few new wires and pulling a few old ones.
After reading this and your first post...I say YAY! The important answer was where you were pulling your power from for the headlights and fans. You want your sense wire to read from this point as you will have it wired. The system will function just like the chevy engineers envisioned. Moving your fusible link near the battery is good for many reasons. Now that wire will also be protected on the run from the battery to the starter.
DUTCH MAX HEADWORK is offline  
post #10 of 15 (permalink) Old Jun 28th, 20, 2:12 PM
Gold Founding Member
Administrator
 
Join Date: Aug 1998
Location: near Kansas City
Posts: 62,893
Garage
Re: Upgrading the electrical in my '72

One thing to keep in mind when thinking about replacing fusible links is the size of the wires they are protecting dictate the fusible link size so you shouldn't use a larger size (amperage wise) fusible link unless you also replace those wires with larger gauge wire.

.
.
.
.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Dean is offline  
post #11 of 15 (permalink) Old Jun 28th, 20, 2:47 PM
Senior Tech Team
 
Join Date: Oct 2003
Location: Saint Louis
Posts: 1,310
Re: Upgrading the electrical in my '72

Quote:
Originally Posted by lucifershammer View Post
Wiring in the '72 is different than others years - the horn relay is up on the firewall next to the booster, and everything connects there. There are no crimped splits or such in the harness like other years have.

The red wire from the alternator goes straight to the horn relay. The orange wire with the fusible link from the starter goes to the horn relay. That is the junction where everything is connected.
I'm not questioning what you have in front of you as far as original wiring but on a diagram from Russ Green it looks like there is a split in the wire between the starter, the alternator and the horn relay ?.

Below is what I saw as for as a split or crimped together connection in the wire from the starter to the horn relay and the alternator as it is connecting three things. If yours is original and different then maybe this needs to be drawn up to show the differences between them ?. I know I have seen running changes in things as to how they are done and maybe if yours does not have this split or connection to the three things like shown below then



Jim

Always working on something:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Jim Streib is offline  
post #12 of 15 (permalink) Old Jun 28th, 20, 6:40 PM Thread Starter
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,644
Re: Upgrading the electrical in my '72

That's a good picture - my car had some work done to it, and I'm guessing they split it out and it is not factory. That looks like it should have been spliced originally, but is now split. I had never seen a proper diagram for the '72 and I know they did a bunch of other electrical changes at the same time, but this must be one that the previous owner did.

Thanks!

Quote:
Originally Posted by Jim Streib View Post
I'm not questioning what you have in front of you as far as original wiring but on a diagram from Russ Green it looks like there is a split in the wire between the starter, the alternator and the horn relay ?.

Below is what I saw as for as a split or crimped together connection in the wire from the starter to the horn relay and the alternator as it is connecting three things. If yours is original and different then maybe this needs to be drawn up to show the differences between them ?. I know I have seen running changes in things as to how they are done and maybe if yours does not have this split or connection to the three things like shown below then



Jim

1972 Chevelle, MJ 467, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
lucifershammer is offline  
post #13 of 15 (permalink) Old Jun 28th, 20, 6:45 PM Thread Starter
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,644
Re: Upgrading the electrical in my '72

I just went back and checked to be sure (since I couldn't remember) - I'm running a 78 amp alternator (internally regulated, removed and jumpered the external regulator connector.)

https://www.rockauto.com/en/moreinfo...68405&jsn=2045

Quote:
Originally Posted by Jim Streib View Post
I knew they did a change on the Chevelle and other GM models wiring in the early to mid 70's.

I did some searching and it looks like a Russ Green did a LOT of documentation on the wiring on his 72 Chevelle.

Just keep in mind that if you are putting in a 94A alternator that is oversized for what you actually need, run a wire that properly supports it's maximum 94A output and then do the same with the wire going to the battery. Should the alternator fail then power will be coming off of the battery feed line and it needs to be large enough to support the loads.

Jim

1972 Chevelle, MJ 467, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
lucifershammer is offline  
post #14 of 15 (permalink) Old Jun 28th, 20, 6:46 PM Thread Starter
Senior Tech Team
Steve
 
Join Date: Sep 2015
Location: Central MA
Posts: 1,644
Re: Upgrading the electrical in my '72

Yup. 10 gauge wire gets a 14 gauge fusible link. 8 gauge wire gets a 12 gauge fusible link.

I've got all the crimpers, wire, fusible link wire, and connectors to pretty much make anything I need.

Quote:
Originally Posted by Dean View Post
One thing to keep in mind when thinking about replacing fusible links is the size of the wires they are protecting dictate the fusible link size so you shouldn't use a larger size (amperage wise) fusible link unless you also replace those wires with larger gauge wire.
Kirk's67SS likes this.

1972 Chevelle, MJ 467, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73
lucifershammer is offline  
post #15 of 15 (permalink) Old Jun 28th, 20, 10:09 PM
Senior Tech Team
 
Join Date: Oct 2003
Location: Saint Louis
Posts: 1,310
Re: Upgrading the electrical in my '72

Quote:
Originally Posted by lucifershammer View Post
That's a good picture - my car had some work done to it, and I'm guessing they split it out and it is not factory. That looks like it should have been spliced originally, but is now split. I had never seen a proper diagram for the '72 and I know they did a bunch of other electrical changes at the same time, but this must be one that the previous owner did.

Thanks!
No problem. I just like to see the right diagrams and who knows sometimes as the car gets older what might have been done to things.

I found a bunch of info from a person named Russ Green and he has pictures of a LOT of the connectors as to what they are and look like, PDF Files with diagrams for power windows and locks, how the horn buzzer is wired in the older horn relays, and something I had never heard about was a diagram on a "Max-Trac" Traction Control System.

Now how accurate this is is anyone guess but I think he is really researching things to not have any mistakes or incorrect information.

Jim

Always working on something:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Jim Streib is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.

Email Address:
OR

Log-in










Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome