Amp meter bypass question

[ferrum]

I'm finally getting around to doing amp meter bypass. I already searched and read multiple amp meter bypass threads on ifsja.org and fsjnetwork. I have parts on order to do this. I would like to do this in phases.

If I were to remove red wire on the alternator off and keep it isolated for now then run new 8 AWG wire(with 80A circuit breaker) from alternator to the starter solenoid without bypassing the amp meter, will it work? Yellow wire will be the one providing power instead of red. When I trace it out on the electrical diagram, it looks like it could work and this would remove charging current to the battery. This may allow me to monitor current that is used in the jeep as well temporarily. I would like to get your opinion/confirmation on this before causing electrical issues on my DD.

[tgreese]

Nope. No current monitoring. Ammeter will be dead.

When you connect the alternator directly to the battery, no or very little current will go through the ammeter. No charging current, no meter action.

How much electricity do you know? Current has to go through the ammeter for it to detect current. There is a calibrated resistance (called a "shunt") in the ammeter. The ammeter is measuring the voltage drop across the shunt. The charging current has to go up to the dash, through the ammeter, and back to the battery for the ammeter to work. When you break that loop, the ammeter is now dead. Everything else should work, but the ammeter will do nothing. Any current to run the the dash will not be sufficient to deflect the meter. Lights, maybe some small deflection, but that does not tell you anything, since the meter will always deflect to the negative side.

Also, why add the circuit breaker? A fusible link is much better for this. That's what Jeep used. Look at the diagram for the CJ wiring and follow that. The six cylinder CJ for 1976 has a Delco 10SI alternator and voltmeter. The V8 CJ for 1976 has a Motorcraft alternator and voltmeter. Are you upgrading the alternator? I don't see a significant advantage to increasing the wire size if you aren't going to a huge alternator.

Realize that the '76 diagram can be confusing. Both the sixes and the V8s are drawn on the same sheet so the charging circuit is duplicated. Start with the alternator type you have and trace from there.

[ferrum]

Nope. No current monitoring. Ammeter will be dead.

When you connect the alternator directly to the battery, no or very little current will go through the ammeter. No charging current, no meter action.

End result is to bypass the amp meter when I can get to it in near future. In the mean time, I like to see what it will read just for fun.

How much electricity do you know? Current has to go through the ammeter for it to detect current. There is a calibrated resistance (called a "shunt") in the ammeter. The ammeter is measuring the voltage drop across the shunt. The charging current has to go up to the dash, through the ammeter, and back to the battery for the ammeter to work. When you break that loop, the ammeter is now dead. Everything else should work, but the ammeter will do nothing. Any current to run the the dash will not be sufficient to deflect the meter. Lights, maybe some small deflection, but that does not tell you anything, since the meter will always deflect to the negative side.

I have decent knowledge of electricity as I deal with building automation system and critical power system for work. I'm a novice when it comes to dealing with automotive electrical wiring so I like to double triple check before I do any changes. I do realize amp meter will deflect to negative side since I'm changing current flow direction. Currently at idle with lights off, amp meter reads near zero amp and with lights on, amp meter reads about 15 amps.

Also, why add the circuit breaker? A fusible link is much better for this. That's what Jeep used. Look at the diagram for the CJ wiring and follow that. The six cylinder CJ for 1976 has a Delco 10SI alternator and voltmeter. The V8 CJ for 1976 has a Motorcraft alternator and voltmeter. Are you upgrading the alternator? I don't see a significant advantage to increasing the wire size if you aren't going to a huge alternator.

While reading threads dealing with amp meter bypass, I ran into bunch using circuit breaker as safety measure and it made sense to me. I'm planning on adding in voltmeter instead of amp meter in future. I'm not upgrading the alternator at this point. Thought was to future proof the alternator wire so all I have to do is change out the circuit breaker size later when I upgrade alternator but wire can be upsized when time comes. Maybe I should just put in 10 awg wire.

Realize that the '76 diagram can be confusing. Both the sixes and the V8s are drawn on the same sheet so the charging circuit is duplicated. Start with the alternator type you have and trace from there.

I looked at the charging circuit. Once I get the circuit breaker, I will make the change. Thanks for confirmation.

[tgreese]

It's really easy to use the existing 10ga wire to go over to the solenoid. The new wire path hangs out in mid-air, and is much shorter than before. Difference between 10 ga and 8 ga in this case has got to be something like one thousandths of an ohm. (A good guess! The difference is 0.000384 ohms/ft ... darn close). When I did this, I removed the bulkhead end of the 10 ga wire, pulled it out of the wire loom and ran it over to the solenoid through a ... fusible link.

The fusible link is superior because it is inexpensive, and foolproof with no moving parts. It's there to protect the Jeep from the battery in the event of a catastrophe, like a wreck. Barring a disaster, you're never going to need a circuit breaker there. Jeep puts two of them in the CJ, one to separate the battery from the alternator, and one to separate the battery from the dash. In the FSJ, only one is required because the charging current is sent through the dash to the battery, so only one current path.

Good luck with your project! The voltmeter tells you whether the voltage feedback to the regulator is working. Very useful IMO. You could get the usual Sunpro part and hang it below the dash until you're ready to modify the cluster.

https://www.amazon.com/Sunpro-CP7985-Cu ... B00029JZXM
https://www.amazon.com/Bussmann-BP-FL-1 ... B001BXR9L8

[ferrum]

I just ordered 14 awg fusible link. I decided to go with your advise on alternator wiring to solenoid connection. I will wire the alternator with 10 awg wire to 14 awg fusible link then to the solenoid.

Thanks

[TitaniaDieKrieger]

I just did the bypass. Here is what I did.
First I took the two fat wires off the ammeter and soldered them together.
Second I found a hot while running port on the fuse box and wired it up to a voltmeter(this will read the charging rate)
I ended up grounding out the voltmeter onto a screw in the firewall.

[ferrum]

I finally had some time available to finish amp meter bypass. I did few things that needed attention a long the way. My heater control was always stuck on defrost. I took it a part cleaned up components and now it works. Changed out instrument light bulbs to led. Installed 5 volt regulator. Changed out amp meter with volt meter. Here’s some photos.


Dark blue 14 awg wires are fusible links.


Volt meter placed.


Voltage regulator install.

Thanks for guidance and making this possible.

[tgreese]

Looks great! That Sunpro meter works well here, and is inexpensive. https://www.amazon.com/gp/product/B0002 ... UTF8&psc=1 Are you picking up switched power from the underlying trace?

[ferrum]

Looks great! That Sunpro meter works well here, and is inexpensive. https://www.amazon.com/gp/product/B0002 ... UTF8&psc=1 Are you picking up switched power from the underlying trace?

At first, I had it hooked up to yellow wire which work great but one issue. Volt meter was always on which I didn’t like. Took it apart again and wired to same as volt regulator source. I didn’t take photo of that setup. When turning signal is on, it bounces volt meter but works good enough.