Help with amp gauge (1 Viewer)

[Geezer Cruzzer]

The amp gauge in the wife's 1982 FJ40 is not working. Did the obvious and pulled the gauge cluster to make sure there were no loose wires. Other gauges working properly. What kind of signal am I looking for when checking with my multi-meter? What else should I check?

 

[John Smith]

Check the two fuses hidden in the wire loom coming off the battery + terminal. Also, be aware the gauge may be working just fine. The later Amp meters barely move, even when working, compared to the early gauge.

 

[bikersmurf]

Shut off the truck & turn on everything electrical... what happens?

It'll show a draw or charge to the battery. If the battery is charged and the alternator is doing its job it'll be sitting at zero.

 

[Geezer Cruzzer]

Thanks for both suggestions. I'll check things out later this afternoon.

 

[Geezer Cruzzer]

Check the two fuses hidden in the wire loom coming off the battery + terminal. Also, be aware the gauge may be working just fine. The later Amp meters barely move, even when working, compared to the early gauge.

Ok, I found one fuse just south of the battery + cable. It tested good. Then all the wires disappear into the harness. Couldn't find another fuse.

As the other responder suggested, I turned on everything electrical with the ignition on and engine off. Then started truck. Needle didn't move.

 

[Landpimp]

also have an 82(and had another) neither had a AMP meter that worked, many many other late models also don't work. I have 2x new AMP meters and not bothered to replace it.

if its still super stock, I think the fuses are wrapped in tape.

there is also a fusible link that plays into the late model AMP meters, the link is NLA but Coolerman can make a new one. I made one for my 82 when I got it, meter still didn't work

all my older Cruisers have working AMP meters....never any issues

 

[Geezer Cruzzer]

I'm still dinking with the amp meter on Miss Scarlet. Been busy with more pressing issues. I've tested the fusible link and found the inline fuse box wrapped in the original factory yellow tape. Fuse tested good. Guess I'm looking a bad amp meter. Can anybody give any help in troubleshoot the gauge itself? Couldn't find anything in the shop books I have.

 

[bikersmurf]

Is it a +/- 30 amp or +/- 50 amp range ammeter?

30 amp have all your juice for the vehicle running through it (other than starter).

50 amp run in parallel to a shunt which carries most of the load.

 

[Geezer Cruzzer]

Sorry, it is a 1982 with a 50 amp. I can turn everything on and the needle doesn't move. How do I test the shunt?

 

[Geezer Cruzzer]

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.

Kept digging in the thread archives and think I answered my own question. The fusible link on the positive terminal is the shunt. Correct?

 

[bikersmurf]

First find it and make sure it hasn't been bypassed by a PO. If it's still there it's most likely working... otherwise you'd have no power. The wiring to the meter would be where I'd suspect a problem... test for continuity with an ohm meter. If wiring and connections to shunt are good then meter is likely faulty. There should be 12v at both wires going to it when they're disconnected.

 

[Racer65]

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.

Kept digging in the thread archives and think I answered my own question. The fusible link on the positive terminal is the shunt. Correct?

I think you're at the right place if you found this discussion. In short, it's a factory design flaw; i.e. "it's a feature not a bug" sort of thing. To fix it you'd need to change the resistance value of the fusible link.

 

[Geezer Cruzzer]

I continued to read the thread quoted above. Though my head would explode on the theory behind this circuit. Someone mentions the fusible link being 6" long. Mine can't be much more than 1". All the connectors and wiring are original and show no signs of overheating. Is this the original fusible link pictured below?

 

[bikersmurf]

More or less... not voltage drop, amperage... Voltage is equivalent to pressure whereas Amperage is the flow (Coulombs per second). The Shunt and Ammeter are designed in a ratio so that only 2% of the current flows through the ammeter.

I'd not consider it a fuseable link... doing so will confuse it with the fuseable link in other models which protects the vehicle from melting down if there's a short.