Another ammeter thread...sorry (1 Viewer)
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Clarification please: I was under the assumption that the newer ammeters were sending a minuscule amount of current to the dash because it was measuring a voltage difference and "interpreting" current vs the older style meters that were actually inline between the battery and alternator.
If this is so, would it matter if the later wiring was hooked up to the earlier gauge as it wouldn't actually be receiving +/- 30a (for the older meter)? Thanks, Taro.
If this is so, would it matter if the later wiring was hooked up to the earlier gauge as it wouldn't actually be receiving +/- 30a (for the older meter)? Thanks, Taro.
All high capacity amp meters use a shunt. The difference in the old and new meters is the location of the meter shunt. On the new ones it is in the engine bay where it is less likely to cause damage in case it burns out. On the old ones, it is built in to the meter.
If you used an early meter in the late chassis, you would have to wire it like the early meters: eg, the large wire from the battery would go directly to the - side of the meter. The + side of the meter goes then to the alternator and the Ign pole of the key. You would not used the fused wires to the fusible link any more with the old style meter.
You might also be able to cut the internal shunt in the old style meter, but this doesn't sound easy or have predicatable outcomes.
If you used an early meter in the late chassis, you would have to wire it like the early meters: eg, the large wire from the battery would go directly to the - side of the meter. The + side of the meter goes then to the alternator and the Ign pole of the key. You would not used the fused wires to the fusible link any more with the old style meter.
You might also be able to cut the internal shunt in the old style meter, but this doesn't sound easy or have predicatable outcomes.
In my opinion the old and new ammeters are not interchangeable at all.
The old one expects to have the entire charge/discharge current to pass through its terminals whereas the new style expects to have only extremely small currents (milli-amps) passing through (generated by voltage-drop across the main fusible link).
Here's a pic of when I was doing some tests. This shows how much movement a voltage drop of 0.17V causes with a latter-style ammeter:
PS. A full-scale deflection requires only 0.3 volts.
And here's a pic of my good needle movement when my fusible link was in poor (frayed) condition and creating good voltage-drop:
In other words, an old-style ammeter would be guaranteed to show even less movement than the usually-imperceptable-movement of a late-model ammeter if connected into late-model wiring the way a late-model ammeter is connected. (But I can't forsee any problems in connecting it up .... It is just that there's no point in doing so because it will be guaranteed to have ZERO sensitivity.)
Wow, thanks for the indepth response!
When I bought my fj40, I was wondering why my ammeter was disconnected. I've only recently realized that the gauge cluster is not original. I bought a period correct ammeter from Specter by accident really ... I thought by ammeter assembly they meant that all of the wiring to the shunt was included.
One of the guys at the shop told me that I didn't need the new ammeter as the old one was working (he hooked it up to a current and saw the needle deflect). So I actually tried to return it, but Specter would not take returns on electrical parts ... so I was bummed until I started pondering this some more.
Btw--a bit of trivia ... what made me realize that my gauge was not stock was that on the '82+ ('79+?) the odometer was supposed to have an extra digit that I didn't have (thanks to Merle and Glen @ Classic Cruisers for this information). Then it made sense as to why my ammeter read +/- 30a
Thanks again!
When I bought my fj40, I was wondering why my ammeter was disconnected. I've only recently realized that the gauge cluster is not original. I bought a period correct ammeter from Specter by accident really ... I thought by ammeter assembly they meant that all of the wiring to the shunt was included.
One of the guys at the shop told me that I didn't need the new ammeter as the old one was working (he hooked it up to a current and saw the needle deflect). So I actually tried to return it, but Specter would not take returns on electrical parts ... so I was bummed until I started pondering this some more.
Btw--a bit of trivia ... what made me realize that my gauge was not stock was that on the '82+ ('79+?) the odometer was supposed to have an extra digit that I didn't have (thanks to Merle and Glen @ Classic Cruisers for this information). Then it made sense as to why my ammeter read +/- 30a
Thanks again!
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...Btw--a bit of trivia ... what made me realize that my gauge was not stock was that on the '82+ ('79+?) the odometer was supposed to have an extra digit that I didn't have (thanks to Merle and Glen @ Classic Cruisers for this information). Then it made sense as to why my ammeter read +/- 30a
Thanks again!
The extra digit on the odometer must have occured at a different time to the ammeter change.
I say this because the "Combination Meter" I was testing in my last post (that has the extra digit) came out of a BJ42 which means it has to be at least 1981.
However my 1979 has the same ammeter but is without the extra digit:
PS. The two Combination Meters have different "arrow-heads" for the blinkers too.
Very interesting! I would have never thought to think about the turn signal lights either. Here's another one: I think around '73? the speedo cable attachment switched from screwing into the back of the speedo to pressing into the back of the assembly. Someone should come up with a trivia game :-D
bj40green
Tssss, tssss
This is my fresh rebuild spare cluster.
"74 to '78, clip speedo cable, 30 Amp meter with internal shunt.
Note the horizontal bar in the gauges for this time period.
Rudi
"74 to '78, clip speedo cable, 30 Amp meter with internal shunt.
Note the horizontal bar in the gauges for this time period.
Rudi
That's what mine looks like. I just realized that I didn't realize the differences because I've never seen a period correct gauge cluster for my '82 before. So now I'm going to have the horizontal bars on all of my gauges except for my ammeter
btw-lostmarbles, apparently the odometers with the seven digits are pretty valuable/rare in the US--asking price was $300-$350 US vs $150 for the six-digit odometers :O
btw-lostmarbles, apparently the odometers with the seven digits are pretty valuable/rare in the US--asking price was $300-$350 US vs $150 for the six-digit odometers :O
And I thought I paid a lot to buy that one for my spare parts bin (at a fraction of that price in cheap kiwi dollars -delivered).
Holy thread revival!
Just out of curiosity, is it going to affect anything if I remove the ammeter from the circuit completely?
Reason I ask is that I've found an aftermarket ammeter that will fit almost perfectly where the OEM one fits.
If I mount it in the same spot, all I need to do is cut the negative track on the back of the cluster where the ammeter bolts to and then run a single cable to the alternator.
Edit: 1982, internal shunt 50A gauge cluster.
Just out of curiosity, is it going to affect anything if I remove the ammeter from the circuit completely?
Reason I ask is that I've found an aftermarket ammeter that will fit almost perfectly where the OEM one fits.
If I mount it in the same spot, all I need to do is cut the negative track on the back of the cluster where the ammeter bolts to and then run a single cable to the alternator.
Edit: 1982, internal shunt 50A gauge cluster.
No problems at all with removing any -50/+50 ammeter. (Nothing at all is dependent on the current flowing through it.)
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bj40green
Tssss, tssss
FYI; up to Dec. 1978 the Ammeter is 30-0-30 A with an internal shunt. In other words.... the full current goes trough the Ammeter.
From Jan. 1979 the ammeter is 50-0-50 A and works with an external shunt. The shunt is a fusible link and from there 2 wires (fused) goes to the Ammeter. In other words: The full current goes trough the fusible link and the Ammeter acts as an voltmeter that measures the voltage drop over the fusible link.
Unfortunately there is a design error and this Ammeter does not reflect what happens electrically speaking.
If this is your problem..... there is a solution for it. You have to make a new fusible link with the correct Ohm value.
Thanks to Mud member Amaurer.
For more info: -► Clusters, Gauges, Speedo & Odo meters
Rudi
I have fuses in there now anyway that I installed when I rewired.
The diesel loom I got with the chassis/engine had the fusible links removed presumably due to previous issues.
The diesel loom I got with the chassis/engine had the fusible links removed presumably due to previous issues.
You are the man! You have saved me a couple of times and this one is great advice also. I ran the tests and it it appearently fried. I sent you a picture of the gauge. It looks as if the solder points inside the gauge at the inside of the studs once had something hooked to them. Am I correct? Thanks for all your help
thanks to the forum for all your help.
bj40green
Tssss, tssss
That´s not OEM, unless that solder is there to keep the bolts in place but it looks like there was a wire soldered between the 2 studs or two wires from those studs to..... who knows.
It looks like it probably was used to hold the studs to the plate to get the bolts tight. What goes wrong when the ammeter does go bad? I tested it as this site said and it did measure bad. It had 12v to the meter, but when hooked up to the meter it showed .1volt or nothing. at the studs
