Can someone dumb down the ammeter bypass for and idiot?

Area for General FSJ related chat.
Post Reply

Topic author
JohnnySwell
Posts: 35
Joined: Wed May 20, 2020 3:36 pm

Can someone dumb down the ammeter bypass for and idiot?

Post by JohnnySwell »

Hey all! I’m a complete rook when it comes to this but I’m in this project to learn new things. Can someone explain the whole ammeter bypass situation like I’m 5 years old haha?

I’ve been told there are a handful of ways to do this and from what I’ve read I’d like to switch it to a typical voltmeter with a new gauge.


Greatly appreciate you guys in this forum!


-Johnny


Sent from my iPhone using Tapatalk
Johnny B

1978 Cherokee Chief

I'd love some input on my build here:
https://www.fsjnetwork.com/forum/viewto ... 12&t=20266
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by tgreese »

You asked for 5yo level....

It would be good to make an effort to read the factory circuit diagram from Jeep, along with any attempt to understand this.

Prior to 1978, the V8 used a different alternator from the inline 6, and Jeep put both schemes on the same drawing. For 1978, they switch to the same Delco alternator for both, but they continued to use most of the same drawing with two alternators. Don't be confused.

Electricity has voltage and current. Similar to water in a pipe, current is the amount (volume of water) and voltage is the potential (pressure of the water). The ammeter measures current (flow) and like a flowmeter, the current must pass through the ammeter to be measured. A voltmeter is different, like a pressure gauge. It requires no flow through it - instead it just inserts itself and measures the pressure. (Not strictly true, but close enough for our purposes).

The alternator creates current to replenish what's drawn from the battery. This current must flow to the battery via a big wire. There is a lot of current, so the wire must be large. The ammeter is in the dash. Thus the current must come from the alternator, go through the firewall and up to the ammeter, through the ammeter, back through the firewall, and to the battery.

Here is the circuit diagram:

Image

Start at the alternator, and see the wire marked 12 RED 10. That's wire number 12 (listed in a table on another page) that's red and a 10 ga wire. Current from the alternator travels along this wire up to the ammeter, and returns to the battery via wire 55A YELLOW 10. You can see that's connected to the starter solenoid via 55B YELLOW 14, a fusible link, which connects to the battery cable.

The ammeter contains a component called a shunt. There are two posts on the ammeter, one at each end of the shunt. When current travels through the shunt, it creates a small voltage which moves the needle on the ammeter. When the shunt gets old, it can heat up and cause the dash fire we want to avoid using a bypass. One way to bypass is to go around the shunt in the ammeter by putting both wires on the same post at the ammeter. This takes the shunt out of the circuit, but the current still flows up to the dash and back to the battery.

Another approach is to take wire 12 RED 10 and connect it directly to the solenoid through a new fusible link. Electricity will always take the easiest route (path of least resistance) and now the charging current will bypass the ammeter route and go direct to the battery. You can then remove the ammeter and some of its wiring, as you see fit. You can't remove everything, since you still need to power the dash and lights ... but you can remove the ammeter and about half of the original ammeter wire.
You do not have the required permissions to view the files attached to this post.
Last edited by tgreese on Sun Jul 11, 2021 1:10 pm, edited 5 times in total.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by tgreese »

There is a sticky thread about this topic at IFSJA: http://www.ifsja.org/forums/vb/showthread.php?t=184890

Read everything there. The secret is to not be confused, and keep going. Eventually you will learn enough that it all starts to make sense. Just refuse to be confused at first.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
User avatar

ghcoe
Posts: 1228
Joined: Sun Nov 03, 2013 6:39 am
Location: SW Idaho

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by ghcoe »

This is a good writeup for the bypass http://stuff.is-a-geek.net/OnlineDocs/V ... bypass.htm . It is pretty simple to do. Good luck! George.
SW Idaho Overlanding Facebook: https://www.facebook.com/SWIdahoOverlan ... page_panel
SW Idaho Overlanding Youtube: https://www.youtube.com/channel/UCYuRx2 ... wVwZJ5oztg
1977 Jeep Cherokee WT
All-Terrain T/A® KO2
Safari Kit
Factory Brush Guard
Factory Tire Carrier
Custom Roof Rack

Topic author
JohnnySwell
Posts: 35
Joined: Wed May 20, 2020 3:36 pm

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by JohnnySwell »

tgreese & ghcoe thanks for the info! It’s starting to makes sense after reading and re-reading.

few questions...

You stated I cannot fully remove the wiring as I need power to the dash. Will this be corrected if I install a voltmeter gauge as in will that replace wiring going to dash? Meaning is it possible for an ammeter delete?

When installing a voltmeter will I be able to reuse any part of the wiring from the ammeter?


I really just want to clean up all wiring and make it as functional and clean as possible

Thanks again!


Sent from my iPhone using Tapatalk
Johnny B

1978 Cherokee Chief

I'd love some input on my build here:
https://www.fsjnetwork.com/forum/viewto ... 12&t=20266
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by tgreese »

No. The original wiring also supplies power to the dash and lights. If you read and understand the wiring diagram, this will become clear.

"Meaning is it possible for an ammeter delete?" Not sure what you mean.

I pointed you to this sticky thread above.

Before is above, after is below.

Image

http://www.ifsja.org/forums/vb/showpost ... ostcount=5

No. You should connect the voltmeter to a source that is switched with the ignition. The ammeter circuit is not switched.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by letank »

the quick and dirty, as Tim laid out, connect battery to alt and my dirty and quick way: connect both ammeter terminals together on the same post of the ammeter... ammeter is electrically bypassed... ALWAYS disconnect battery when doing electrical work... Of course do this with battery disconnected

Good luck
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by tgreese »

letank wrote: Thu Jul 15, 2021 10:32 am Of course do this with battery disconnected
Yes, the ammeter is alive all the time! It's directly connected to the battery by a big wire.

When I did this to my J20, I did not remove any wires. I took wire 12 RED 10 out of the bulkhead connector at the firewall, cut it to length, spliced on a fusible link and connected it to the battery at the solenoid. The wire from splice B to the backside of the bulkhead I abandoned in place.

I also did the voltmeter conversion shown in several other threads (no link right now). The voltmeter installation is all in the cluster - you connect one wire to a ground on the cluster and the other to the ignition on the cluster. Easy. Don't recall exactly, but I think I buffed off one of the traces on the cluster and soldered the wire to it. Many ways to do this.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

BillBertin
Posts: 6
Joined: Fri May 14, 2021 5:51 pm

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by BillBertin »

This is a great post. I also apparently needed an explanation like this. Thank you y'all. wp.

rapom
Posts: 82
Joined: Sun Jul 31, 2016 10:00 am

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by rapom »

Another way to read volts is to buy a usb cigarette lighter plug. I have one that also reads volts.

ffdfrontman
Posts: 3
Joined: Sun Jul 18, 2021 7:02 am

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by ffdfrontman »

Great thread and help. This makes a lot more sense to me now.

Only question I have for the bypass fuse what amp fuse link are you using?
Jereme Robinson
Cypress, Texas
1982 Jeep J10 (Wile E. Coyote) 258i6 44/20 4speed np208
2017 Jeep JKU
2020 Jeep Gladiator (gave up the ghost and sold back to jeep)
1984 Jeep CJ7 i4, still factory stock as my dad bought it in 83.
User avatar

tgreese
Posts: 7117
Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by tgreese »

I did not use any fuses, instead a fusible link. Much better than a fuse for this purpose. The size is determined by the wire it is protecting. A 10ga wire is protected with a 14ga fusible link. A 12ga wire is protected by a 16ga fusible link. And so forth.

Here's what I used - https://www.amazon.com/Bussmann-BP-FL-1 ... B001BXR9L8

The link does not need to be overly long, but it should be long enough so the center heats up when overloaded. It's basically wire with a special insulation that contains the melting wire and protects its surroundings.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

ffdfrontman
Posts: 3
Joined: Sun Jul 18, 2021 7:02 am

Re: Can someone dumb down the ammeter bypass for and idiot?

Post by ffdfrontman »

Makes perfect sense thank you Tim.
Jereme Robinson
Cypress, Texas
1982 Jeep J10 (Wile E. Coyote) 258i6 44/20 4speed np208
2017 Jeep JKU
2020 Jeep Gladiator (gave up the ghost and sold back to jeep)
1984 Jeep CJ7 i4, still factory stock as my dad bought it in 83.
Post Reply