Ampmeter Wiring 1968 - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 17 (permalink) Old Nov 3rd, 13, 10:04 AM Thread Starter
Tech Team
Russ
 
Join Date: Jan 2012
Location: 1968 El Camino SS396
Posts: 208
Ampmeter Wiring 1968

1968 El Camino SS Numbers Matching Original.
I'm installing a stock gage cluster in place of my stock idiot light cluster and I'd like some help on the ampmeter wiring. It may sound silly but I'm going to retain the idiot lights and just relocate them to like small leds in another location. All the threads on the subject are really confusing and alot doesn't apply to my specific installation.
I have a single lead alternator which I guess was a replacement.
I'd like to run 2 new leads from the stock, in dash amp gage. Could someone tell me where to connect these 2 leads ?
Thanks
kernal is offline  
Sponsored Links
Advertisement
 
post #2 of 17 (permalink) Old Nov 3rd, 13, 8:51 PM
Gold Member
Joe
 
Join Date: Aug 1998
Location: Lincoln, NE
Posts: 4,477
Re: Ampmeter Wiring 1968

You'll have to run 2 additional wires from the interior of the vehicle to the engine bay.

One wire needs to connect the horn relay's screw lugs (where the constant battery (+) power connections are tightened down) and the other wire needs to connect to the junction block behind the battery that has the fusible link bolted to from the battery's (+) terminal. Each wire connects onto the input lugs of the ammeter.

The factory used 20 gauge fusible links at each location to protect the long runs of otherwise unprotected wires into the vehicle's interior. The problem is, the fusible link only blows under a massive short condition (like a feed getting pinched to ground). If there was simply a large amount of current thru the ammeter on accident (where the cars's main power feed from the battery junction block the horn relay was loose or corroded, the ammeter circuit looked like a simple pathway), the ammeter would get damaged. One thought would be install a rubberized fuse holder and install a 2 amp ATO fuse in it. Use this instead of the fusible link at the "behind the battery" location so it can't be seen by judges.

I don't know which lug is which on the ammeter for a '68. If you wire it wrong, you'll show charging in the "+" region of the gauge when the engine is off and the headlights are on. At that point, all you'll have to do is swap the wires at the back of the guage.

-If you don't stand for something, you'll fall for anything.
Coppertop is offline  
post #3 of 17 (permalink) Old Nov 3rd, 13, 11:35 PM
Team Member
Steamy
 
Join Date: Jul 2003
Location: Here&there, AR
Posts: 6,818
Wink Re: Ampmeter Wiring 1968

Dash back connections-


At the inside bulkhead connector-



I'll have to look at my car to see which wire goes to the relay and which to the junction block. It won't blow the gauge if it's hooked up backwards, it just reads incorrectly. BTDT
BillL

If you keep on livin', you're gonna get old.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Good health is merely the slowest possible rate at which one can die.
Good livin' will speed it up, but it's worth it.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


My Showroom

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Ark68SS is offline  
 
post #4 of 17 (permalink) Old Nov 4th, 13, 12:11 PM Thread Starter
Tech Team
Russ
 
Join Date: Jan 2012
Location: 1968 El Camino SS396
Posts: 208
Re: Ampmeter Wiring 1968

Thanks guys, that's a big help. I'll give it a try.
kernal is offline  
post #5 of 17 (permalink) Old Nov 5th, 13, 1:54 PM Thread Starter
Tech Team
Russ
 
Join Date: Jan 2012
Location: 1968 El Camino SS396
Posts: 208
Re: Ampmeter Wiring 1968

Is the gage of the wires to the amp important?
kernal is offline  
post #6 of 17 (permalink) Old Nov 5th, 13, 2:27 PM
Team Member
Steamy
 
Join Date: Jul 2003
Location: Here&there, AR
Posts: 6,818
Wink Re: Ampmeter Wiring 1968

16ga is sufficient, use 14ga if you want a little insurance. Definitely use Joe's tip about the 2 A fuse at the junction block.
BillL

If you keep on livin', you're gonna get old.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Good health is merely the slowest possible rate at which one can die.
Good livin' will speed it up, but it's worth it.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


My Showroom

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Ark68SS is offline  
post #7 of 17 (permalink) Old Nov 6th, 13, 12:36 PM Thread Starter
Tech Team
Russ
 
Join Date: Jan 2012
Location: 1968 El Camino SS396
Posts: 208
Re: Ampmeter Wiring 1968

Thanks, I'll use the 2amp fuse. This may be a stupid question, but which wire should be fused. If I connect to the lug behind the battery for one lead and the horn relay for the other, it looks like there's already a heavy wire running directly from the lug to the relay, so both ampmeter leads will always have 12v. I can't quite grasp what the fuse will protect.
What am I missing? I tried to connect a stewart warner amp gage up for a test - one term to the lug behind the battery and the other to the large terminal on the horn relay (which is essentially each end of an existing wire) and I get nothing on the ampmeter.

Last edited by kernal; Nov 6th, 13 at 2:23 PM.
kernal is offline  
post #8 of 17 (permalink) Old Nov 6th, 13, 6:28 PM
Lifetime Premium Member
Darren
 
Join Date: Mar 2004
Location: Omaha, NE
Posts: 2,833
Garage
Re: Ampmeter Wiring 1968

The fuse protects the gauge and the long run of wires. Yes both are hot all the time; the gauge just shows variances in load on the system. Youíll most likely see it move a little to the ď-ď side every time the signals flash, etc.

If you donít push the limits how are you going to find the weak spots?
USMC- Retired
My car: 1970 Chevelle

Factory 12 bolt /4-Speed Malibu -Dual stage wet nitrous with heater & purge - Holley Strip Dominator, Speed Demon 750 CFM - (All MSD distributor, blaster 3 coil, 6AL, & 3 stage retard) - 4 wheel disk brakes - Aeromotive Fuel system Ė Boss 338 18ís - BMW 5.25 true HID projector mod - and of course... the FLAPPER - bla, bla, bla.. lots of other expensive stuff I canít remember
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
70 nialator is offline  
post #9 of 17 (permalink) Old Nov 6th, 13, 7:53 PM
Gold Member
Joe
 
Join Date: Aug 1998
Location: Lincoln, NE
Posts: 4,477
Re: Ampmeter Wiring 1968

Quote:
Originally Posted by kernal View Post
Thanks, I'll use the 2amp fuse. This may be a stupid question, but which wire should be fused. If I connect to the lug behind the battery for one lead and the horn relay for the other, it looks like there's already a heavy wire running directly from the lug to the relay, so both ampmeter leads will always have 12v. I can't quite grasp what the fuse will protect.
What am I missing? I tried to connect a stewart warner amp gage up for a test - one term to the lug behind the battery and the other to the large terminal on the horn relay (which is essentially each end of an existing wire) and I get nothing on the ampmeter.
Russ,

The factory harness (on vehicles that were ordered with ammeters) had 20 gauge fusible links at each location--one at the horn relay and one at the battery junction block. You are correct, both wire are hot at all times, even when the vehicle is off. That's why the fuse links were installed to protect these long runs of wire that always had 12 volts. If one got shorted to ground, the fusible link would burn up to protect from a fire starting.

Unfortunately the fusible links do nothing to protect the fragile ammeter movement. That's why I suggested the 2 amp fuse. Ideally (assuming you aren't building a show car), would be to intalled two fuse holders, one at each location, and each holding a 2 amp fuse.

For those that have show cars, having something un-original like a fuse holder hanging out is a big no-no, that's why you install one behind the battery where no one can see it. You don't have that luxury at the horn relay as there is no place to hide a fuse holder.

The engineers never foresaw these vehicles being around this long. What happens over the years is the main power connections get loose, or corroded (or a careless owner doesn't maintain them). Now what happens is someone tries to start the car and scores of AMPS are drawn thru this alternate route (remember the ammeter and it's wire looks like a bypass to the main 10 gauge wire running across the radiator support). The 20 guage fusible links won't blow in time to save the ammeter's internals. This is why I suggest at least one 2 amp fuse in line with this circuit. It blows to protect the meter itself.

This is the exact situation that has some many 70-72 owners scratching their heads on why their printed circuit board traces connecting the ammeter are burnt to a crisp "for no apparent reason"....

-If you don't stand for something, you'll fall for anything.
Coppertop is offline  
post #10 of 17 (permalink) Old Nov 6th, 13, 8:58 PM
Team Member
Steamy
 
Join Date: Jul 2003
Location: Here&there, AR
Posts: 6,818
Wink Re: Ampmeter Wiring 1968

Quote:
Originally Posted by kernal View Post
I tried to connect a stewart warner amp gage up for a test - one term to the lug behind the battery and the other to the large terminal on the horn relay (which is essentially each end of an existing wire) and I get nothing on the ampmeter.
Did you put a load on the system? With no load out or charge in, the needle will just sit in the middle. An ammeter only shows the rate of charge or discharge, not the battery's state of charge.
If the wiring's not finished on the car yet, make some jumpers and run a wire from the horn relay buss to one terminal of a headlight and another wire from the other headlight terminal to the - battery post and see if the needle moves.

BillL

If you keep on livin', you're gonna get old.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Good health is merely the slowest possible rate at which one can die.
Good livin' will speed it up, but it's worth it.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


My Showroom

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Ark68SS is offline  
post #11 of 17 (permalink) Old Nov 7th, 13, 1:19 PM Thread Starter
Tech Team
Russ
 
Join Date: Jan 2012
Location: 1968 El Camino SS396
Posts: 208
Re: Ampmeter Wiring 1968

Quote:
Originally Posted by Ark68SS View Post
Did you put a load on the system? With no load out or charge in, the needle will just sit in the middle. An ammeter only shows the rate of charge or discharge, not the battery's state of charge.
If the wiring's not finished on the car yet, make some jumpers and run a wire from the horn relay buss to one terminal of a headlight and another wire from the other headlight terminal to the - battery post and see if the needle moves.

BillL
The car is running. I'm putting a new dash together for a later swapout.
I would think with the engine running, as I had it, that the meter would show a charge instaed of just sitting in the middle with no motion, especially when reving the engine. I'm sure the alternator's working since I drive the car all the time and the voltmeter reads fine. I verified 12v at each of the 2 jumpers to the meter. It is really correct to connect to the the large terminal on the horn relay which means the meter ends up being connected to each end of about a 4' 12v wire?
kernal is offline  
post #12 of 17 (permalink) Old Nov 7th, 13, 4:07 PM
Team Member
Steamy
 
Join Date: Jul 2003
Location: Here&there, AR
Posts: 6,818
Wink Re: Ampmeter Wiring 1968

Quote:
Originally Posted by kernal View Post
It is really correct to connect to the the large terminal on the horn relay which means the meter ends up being connected to each end of about a 4' 12v wire?
Yep, an ammeter is wired in series, not parallel. The ammeter is measuring the current along that stretch of wire and will tell you if the current is increasing (flowing into the battery) or decreasing (flowing out of the battery) through the section of wire that the ammeter is spliced into.
That's a little oversimplified but understandable.

EDIT: That's the way a "normal" ammeter works. See Joe's post below for the Chevelle version.


Look at the meter when you're starting the car. The starter current should make the meter show a fairly substantial drop.

Does your car have the standard 3-wire alternator with an external voltage regulator? If not, based upon where the B+ wire (big red one) from the alternator is connected it will make a difference. If the B+ wire goes directly to the battery, then you won't show charging amps with the factory wiring.
BillL

If you keep on livin', you're gonna get old.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Good health is merely the slowest possible rate at which one can die.
Good livin' will speed it up, but it's worth it.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


My Showroom

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

Last edited by Ark68SS; Nov 7th, 13 at 10:30 PM.
Ark68SS is offline  
post #13 of 17 (permalink) Old Nov 7th, 13, 7:24 PM
Gold Member
Joe
 
Join Date: Aug 1998
Location: Lincoln, NE
Posts: 4,477
Re: Ampmeter Wiring 1968

Actually the Chevelle/El Camino/Monte Carlo guages feature an "ammeter" that actually is a small voltmeter.

A traditional ammeter is indeed in series with a load. I'm wondering if your Stewart Warner is a traditional meter, in which it won't work properly in the GM design.

With the GM design, the meter is a millivolt meter. It "reads" the voltage drop across the wire that runs from the battery junction block to the horn relay connections. It actually is in parallel with the main current path. A very small voltage drop in developed across the factory battery power feed. 0.5 volts will cause a reading of approx. 40 amps on the gauge. Which way the needle swings (into charge or discharge area) depends on the polarity seen between the two "ammeter" connections.

As Bill stated, something like starting the vehicle will let you know if the meter is working correctly. Headlights on with engine off will also cause a deflection.

A normally operating vehicle will show little or no deflection. It may rest slightly in the "+" region. Remember, this isn't an issue, as a massive current is the only way to get definitely deflection and you won't see that in a systems-normal vehicle.

Bill is also correct on the wiring. If you deviate in your charging system wiring, then all bets are off as GM designed the system to work specifically with the original layout.

-If you don't stand for something, you'll fall for anything.
Coppertop is offline  
post #14 of 17 (permalink) Old Nov 8th, 13, 12:32 PM Thread Starter
Tech Team
Russ
 
Join Date: Jan 2012
Location: 1968 El Camino SS396
Posts: 208
Re: Ampmeter Wiring 1968

"Does your car have the standard 3-wire alternator with an external voltage regulator? If not, based upon where the B+ wire (big red one) from the alternator is connected it will make a difference. If the B+ wire goes directly to the battery, then you won't show charging amps with the factory wiring."
=======================
Well that must be the problem. My 3 wire alternator has been replaced with a single wire one. The old connector is still in the harness but there is just one big red wire off the alternator. I haven't traced it but I almost think it runs right to the horn relay which then has the other big wire to the battery lug.
In this case is there a way to connect the ampmeter?

Last edited by kernal; Nov 8th, 13 at 8:13 PM.
kernal is offline  
post #15 of 17 (permalink) Old Nov 8th, 13, 9:59 PM
Gold Member
Joe
 
Join Date: Aug 1998
Location: Lincoln, NE
Posts: 4,477
Re: Ampmeter Wiring 1968

Quote:
Originally Posted by kernal View Post
=======================
Well that must be the problem. My 3 wire alternator has been replaced with a single wire one. The old connector is still in the harness but there is just one big red wire off the alternator. I haven't traced it but I almost think it runs right to the horn relay which then has the other big wire to the battery lug.
In this case is there a way to connect the ampmeter?
Russ,

From what it sounds like, I don't think that's your problem (if there truly is one). Most people just buy a 1-wire and install it. Red wire to lug on back of alternator. Done. What Bill was referring to is when people actually reroute factory wiring. Many times owners will actually install their own large red wire from the alternator, right to the battery's + post.

If the harness wrapping/wiring doesn't appear to be messed with, I doubt someone has gotten into changing things...

-If you don't stand for something, you'll fall for anything.
Coppertop 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









Old Thread Warning
This Thread is more than 2166 days old. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
If you still feel it is necessary to make a new reply, you can still do so though.

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