Capacity of Ammeter (1 Viewer)

Cruiserdrew

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1976 Instrument Panel

My FJ40 is currently being rewired by TrickyT and myself. We are basically trying to duplicate the layout/function of the factory system using a Kwik Wire harness.

The current plan is to keep the Ammeter, wired per the factory. The problem is, the alternator is being upgraded from 40 amps (stock) to a 60 amp unit out of an FJ60. The external voltage regulator will be eliminated.

Since the charging circuit runs through the Ammeter, can it handle the theoretical possibility of 60 amps coming out of the alternator (like charging a dead battery)? The meter only reads to plus and minus 30 amps.

I searched this until my eyes glazed over-but I believe the 1976 ammeter would be shunted internally, not externally like the 79 and up FJ40s.
 
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I just was looking at one. It has a solid metal bar going through it. The magnetic field generated from the power running through it causes the needle to move. I'm hesitant to hook power from my 120 amp alternator, but I'd not be concerned about 60 amps. The alternator in my 1974 was tested and I was told it put out 50-55 amps, and I never had any problems.

Some of the newer clusters have one that goes up to +/- 50 amps if you wanted to be able to see higher measurements.
 
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I'm guessing here, but I imagine it would handle it for the primary reason that it won't see the full output of the amp meter for long. The rating of the wires is conservative and the rating maximum is for continuous duty. Typically the amp meter will put out 10-15 A after starting for 10 minutes to recharge the battery. If the battery was fully discharged, it might put out the full 60A, but it would only do this for a short time until the battery was partially charged, when it would start to drop. Worst case is that you fry the meter.

Theoretically, if you doubled the internal shunt, you would double the range of the meter. It isn't so easy to break into them to stack the shunts.
 

Cruiserdrew

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Can you post some pictures, tips, and advice on using Kwik wire harnesses... Got one waiting to go in.


I think we'll get back to it this weekend.

Tips:

1-Use your factory harness if at all possible. Seriously the column is hard and the flashers and turns are very difficult due to the differences between GM and Toyota. All the Hot-Rod type harnesses are basically GM conventions.

2-Get a bunch of Toyota style connectors from Coolerman. I got more than needed, but it's good in the sense, I have enough and won't run out.

3-Test every circuit as you install tracing the power through each one.

4-Save your old harness as you will salvage tons of connectors with pigtails.

5=Write down what you did.

6-Have a friend that is comfortable with electricity and can read wiring diagrams like comic books.

7-Don't know if this is right, but we are trying to basically duplicate factory conventions. For instance, the ammeter is hooked up, and the rear part of the harness will connect through a factory connector like stock. The easy way would be to run the alt directly to the battery, but then you loose the function of the ammeter.

8-Have the wiring diagram for you year available and write down where you make changes.

The Kwik Wire harness is a quality unit with very nice wires but it isn't Toyota. It's the interface between the two that's hard.
 

bj40green

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I'm guessing here, but I imagine it would handle it for the primary reason that it won't see the full output of the amp meter for long. The rating of the wires is conservative and the rating maximum is for continuous duty. Typically the amp meter will put out 10-15 A after starting for 10 minutes to recharge the battery. If the battery was fully discharged, it might put out the full 60A, but it would only do this for a short time until the battery was partially charged, when it would start to drop. Worst case is that you fry the meter.

Theoretically, if you doubled the internal shunt, you would double the range of the meter. It isn't so easy to break into them to stack the shunts.

X2 on what Pin_Head wrote.
If your battery is empty/dead you can't crank the engine. So let's say you jump start your truck. The alt is only putting out power at rpm's higher then idle. Since you are the one with the foot on the pedal, you're also the one with the eye on the ammeter. In other words: you can control the recharge by pulling the throttle a bit until the the needle reaches 30Amp and let it run for a few minutes until the needle drops.

Forget about the '79 and later ammeter. That one uses the fusible link as a shunt to measure the current.

If you're interested in the "how it works" see page 4 posting 74 in this thread: https://forum.ih8mud.com/40-55-series-tech/544543-clusters-gauges-odo-meters.html

Rudi

[EDIT]: When you do a jump start, the donor truck is already charging your battery so no worries.
 
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