Ammeter bypass and aftermarket gauges.

[BlistAbody]

Hi everyone. I bought new gauges and gauge cluster for my 73 Dart Sport. Seems to be more of a job than I originally thought so if I could get some input from anyone who has done them before, that would be swell.

My first issue is how to properly bypass the ammeter. I've seen it to where you route the alternator straight to the starter relay with 10 awg wire and a fusible link, but then what do you do with the black and red wires that directly hook up to the ammeter?

The next question is what everyone does for the power and ground for the gauges. Where do you get your switched power from? I don't want to overload an existing current. Can they all share the same ground?

Thanks for your help. I'm not an electrical expert so bear with me haha. They are Jegs branded gauges

 

[DartGTDan]

Here's what I did on my '71 Dart GT (318, A904).

Follow the fat RED ARROWS on the picture. Hopefully this all makes sense to you.

I disconnected the original 10RD wire on the Starter Motor Relay (and taped it back in the harness).

Then I disconnected the original 12RD wire on the AMMETER "INPUT" stud (and taped it back in the harness).

Then I added a 8RD wire between the Starter Motor Relay and the BATTERY + Lug.

Then I added a 12RD wire (with a 16-gauge fuse link) from the BATTERY + Lug to AMMETER "OUTPUT" stud (stacked onto the original 12BK wire (making 2 wires on that stud).

I also added a 12RD wire (with a 16-gauge fuse link) from the ALTERNATOR stud to the BATTERY+ Lug.

 

[MadScientistMat]

Bypassing the ammeter just requires hooking the black and red terminals together and taping them off, or better, splicing the wires together with a high quality crimp terminal.

It sounds like you're more concerned about bypassing the bulkhead connection. There are several ways to do this; my preferred would be to run the charging wire from the alternator to the battery lug on the starter relay or the battery positive terminal and run the 12v power through a separate high current bulkhead connector. A bolt through a grommet with a ring terminal on each side can work.

 

[timk225]

Here's a good video on what the wires to and from the ammeter are all about. Long story short, the alternator output goes through the bulkhead connector, to the ammeter, back through the bulkhead connector, and to the starter relay. That could all be eliminated, the only downside being no ammeter.

Whoever had my 1973 Duster before me rigged up different wires. Instead of using the OEM wiring harness and bulkhead connector, a different, independent wire goes from alternator to ammeter, then a different wire from ammeter to starter relay. The bulkhead connector, especially when 50 years old, doesn't like huge amounts of power running through its small connectors. I should change those wires the previous owner installed just because they are old, but I haven't done it yet.

 

[Mattax]

Long story short, the alternator output goes through the bulkhead connector, to the main splice

Fixed.

The ammeter is only involved in the battery feed/charging circuit. Other than that it has nothing to do with powering the car.
Do not wire around the fusible link in the battery circuit in such a way as to remove protection from the battery shorting.

 

[Mattax]

Whoever had my 1973 Duster before me rigged up different wires. Instead of using the OEM wiring harness and bulkhead connector, a different, independent wire goes from alternator to ammeter, then a different wire from ammeter to starter relay. The bulkhead connector, especially when 50 years old, doesn't like huge amounts of power running through its small connectors. I should change those wires the previous owner installed just because they are old, but I haven't done it yet.

Could be one of the heavy duty options. Several threads about those. Most common with rear window defrost. Or could just be a fix like you say. easy to tell most of the time.

 

[crackedback]

You could totally remove the black wire from alternator to bulkhead. Run a direct charge wire with a fusible link in it

Make a Y splice attached to the OEM red/fusible link and feed all the interior/dash harness via two bulkhead connectors. Although I've seen plenty of smoked dash harnesses, especially the blue ignition wire, where the OEM link did nothing to stop damage.

Bypass the ammeter as it is not responsive any longer to the required current.

No cutting or chopping up the OEM stuff.

I know a guy that builds that stuff...

 

[RustyRatRod]

I know a guy that builds that stuff...

How do you get along with that guy? I hear he can be a real twatwaffle.

 

[BlistAbody]

Thanks everyone for your help, I appreciate it.

 

[BillGrissom]

Best to bypass the ammeter within the engine bay. If you just put red and black on the same stud on the ammeter, you don't solve the problem of that high current going thru the bulkhead terminals to often melt them. Not a problem in 1963 and 1965 cars since they use clamped buss-bars for that rather than spade terminals, indeed I put a bulkhead from a 1965 Fury in my 1964 Valiant to get that (had to cut opening 1/8" taller). What you propose does the bypass in the engine bay. You could keep the ammeter wired as is and perhaps the needle will still indicate slightly, to let you know "charge or discharge".

The ammeter isn't essential since you can use a cig-lighter voltmeter to verify the alternator is working on road trips. I do that in my newer cars. Should read ~14.3 VDC with engine running and ~12.6 VDC stopped (after sitting 20 min) if the battery is fully charged. Helped us once in our 2002 Chrysler minivan after driving thru water, to trigger a warning lamp on the dash. I plugged in the voltmeter and was happy to see 14.3 VDC, so figured that lamp doesn't reset until you turn off the engine. Made it home, and powering off did reset the lamp. Wasn't going to stop, since after midnight on Jan 1 with floods all over, and we had already diverted from closed CA 99, crossing vineyards on a 2-lane with water flowing across the road to reach I-5.

I went big in my 3 1960's Mopars. I ran a thick bypass wire from ALT Out to Batt+ (via new fuse/relay box), but thru parallel-flipped diodes. In my 273, I used the factory cable from a 1990's Magnum V-8. That builds up ~0.75 V drop at ~50 A, which moves the dash ammeter needle, and the voltage drop doesn't increase much as current increases beyond that, so think of it as a relief valve. Posted ~2010. Search for "Modernized Engine Wiring" for details, but don't even consider it unless you understand electronics well (engineer or tech). Based on some of the gomer replies to my post (one guy arguing with an engineer - me), most people here don't have the knowledge, and are unwilling to learn.

 

[72RoadRunnerGTX]

Here's a good video on what the wires to and from the ammeter are all about. Long story short, the alternator output goes through the bulkhead connector, to the ammeter, back through the bulkhead connector, and to the starter relay. That could all be eliminated, the only downside being no ammeter.

There is another very dangerous downside to this simple “shunt wire” bypass.

 

[BillGrissom]

There is another very dangerous downside to this simple “shunt wire” bypass.

True. I ran my ALT to BATT+ cable thru a fuse, in all my Mopars, plus the high-current diodes I mentioned. Easy to find a say 150 A, 32 VDC fuse you can bolt in-line. Or might use a "marine fuse" w/ holder and replaceable fuse. I did that in my home solar system batteries since 32 VDC rating doesn't suffice (51.2 VDC), but the marine fuses are rated higher (100 VDC? forget). In 1990's Magnum V-8 Jeeps, the thick cable from ALT to BAT+ runs thru a large fuse in the underhood fuse/relay box. I used that Jeep box in my old Mopars.

 

[72RoadRunnerGTX]

True. I ran my ALT to BATT+ cable thru a fuse, in all my Mopars, plus the high-current diodes I mentioned. Easy to find a say 150 A, 32 VDC fuse you can bolt in-line. Or might use a "marine fuse" w/ holder and replaceable fuse. I did that in my home solar system batteries since 32 VDC rating doesn't suffice (51.2 VDC), but the marine fuses are rated higher (100 VDC? forget). In 1990's Magnum V-8 Jeeps, the thick cable from ALT to BAT+ runs thru a large fuse in the underhood fuse/relay box. I used that Jeep box in my old Mopars.

To be clear, for the Chrysler ammeter-based charging/load distribution system from this time, even if the added shunt wire bypass has its own circuit protection, it will parallel the stock circuit protection device (16ga fusible link) for all stock under dash unfused wiring. Effectively defeating this original circuit protection for the stock wiring. Should a short occur, wires will burn with this shunt in place, with or without its own fusible link. Other steps need to take place to ensure complete and accurate circuit protection for all vehicle wiring. This so-called “shunt wire”, under-hood ammeter bypass is very dangerous when performed as most of those who promote it, say should be done.

 

[Mattax]

Sizing is a challenge when selecting protection.

A 16 gage fusible link will more or less protect a 12 gage wire from a high current dump.
Two 16 gage links in parallel will not protect a 12 gage wire well if at all.

I doubt a 150 amp fuse will protect a 12 gage wire. The diodes are interesting idea - I'm assume they are allowing only charging and blocking current reverse.
Mr. Knize thought 160 Maxi fuse might protect an 8 gage wire. (toward bottom of the page). I'm not so sure.

Electrical Issues - MiniMopar Resources

www.minimopar.net

According to this very rough guide, a 12 gage wire should be able to handle 41 amps continuous at 30*C (inside passenger compartment).
And 8 gage (SAE) can handle 65 amps continuous at 50*C (engine bay)

WireSizer User Guide

Learn how to use WireSizer to size wire gauge, understand voltage drop results, and choose safe wiring options for DC circuits.

www.wiresizer.com

The better calculators are more like this one

Wire Size Calculator

IIRC there is also a better one at Blue Sea's website which lets one input the temperature.

One of the interesting aspects of power feeds for both the Mini-mopars and the 1986-91 Jeep SJ is the use of even smaller fusible liks on some of the feeds. Presumably there is other equipment or smaller wires downstream that need protection.

Side note: If the battery is sucking 40 amps that could end very badly.

 

[BillGrissom]

To be clear, for the Chrysler ammeter-based charging/load distribution system from this time, even if the added shunt wire bypass has its own circuit protection, it will parallel the stock circuit protection device (16ga fusible link) for all stock under dash unfused wiring. Effectively defeating this original circuit protection for the stock wiring. Should a short occur, wires will burn with this shunt in place, with or without its own fusible link. Other steps need to take place to ensure complete and accurate circuit protection for all vehicle wiring. This so-called “shunt wire”, under-hood ammeter bypass is very dangerous when performed as most of those who promote it, say should be done.

I see your point. The engine bay shunt bypasses both the Ammeter and the fusible link. One solution might be to connect it on the far side of the fusible link (opposite battery side), but then all alternator current must flow thru that fuse when recharging the battery. True also in the OE design, and why the fusible link was sized for ~30 A (max alternator of the day). But many owners upgrade the alternator to handle things like a radiator fan. A better solution is to add a fuse (or fusible link) to the ALT wire that feeds the cabin, via Bulkhead terminal 18 (in video), and size it 30 A or less (max cabin draw expected). If room, you could mount it on the ALT output stud. A fuse on the bypass cable should be sized for the max output of the alternator.

Readers who have done home wiring know that 12 awg wire is rated for 20 A in houses. But that is for wire buried in insulation. If in the open, like in appliance apps, 12 awg is rated for 40 A. Why Mopar decided 12 awg sufficed for the 30 A alternator output.