Loss of ammeter sensitivity (1 Viewer)

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weagle99

weagle99

Joined
Jun 12, 2010
Threads
22
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282
Location
North Augusta, SC
I recently replaced the ingnition switch in my stock '72 and noticed that I lost a good bit of senstivity in the ammeter after the work was completed. Before the needle would freely jump around when the engine was revved, turn signals were on, etc., but now it basically stays just above 0 (towards 30+) with very little movement when the truck is being used.

Dumb coincidence? Ammeter going bad? I am worried that I could be stranded somewhere if the guage dies completely.

Thanks in advance.
 
Last edited:
actually, it sounds more like you fixed a short you had earlier - it's not supposed to wildly swing

normal operation is at 0, with deflecting to - when you have a lot of devices on, like headlights and heater together
 
Last edited:
DSRTRDR said:
actually, it sounds more like you fixed a short you had earlier - it's not supposed ti wildly swing

normal operation is at 0, with deflecting to - when you have a lot of devices on, like headlights and heather together
Click to expand...

I think you solved a bad contact problem by replacing the switch which makes it a lucky coincidence.
There must have been a reason to replace that switch.

Rudi
 
Thanks for the replies. The old universal ignition switch installed by the PO was failing because at times I would turn the key and nothing would happen. I verfied the problem with the switch by checking continuity after it was removed. I installed a Toyota switch and the now the ignition is working correctly.

I was just surprised at the change in the meter behavior. I literally have to look closely to see the slight movement of the needle, which as I mentioned is a big difference from the noticeable deflection before.
 
My 79's amp meter that I have had for 14 years hardly moves and I thought this was normal. Just a little - of 0 with the key on but engine off and then just a little + with engine running. Never moves more than the amp needle's width.
But having just put a low mileage and all original 74 on the road and seeing its large range of needle movement I think something is wrong with the 79's.
Sorry this post is not any help in fixing your's . But I will be tryng to fix my 79's as it goes back together.
 
456z said:
My 79's amp meter that I have had for 14 years hardly moves and I thought this was normal. Just a little - of 0 with the key on but engine off and then just a little + with engine running. Never moves more than the amp needle's width.
But having just put a low mileage and all original 74 on the road and seeing its large range of needle movement I think something is wrong with the 79's.
Sorry this post is not any help in fixing your's . But I will be tryng to fix my 79's as it goes back together.
Click to expand...

Save yourself the trouble of diving into this problem.
From Jan. '79 the Ammeter circuit changed. The Gauge changed from 30-0-30 to 50-0-50 and the circuit to measurre this was changed from "Full Current" throug the gauge into a shunt system where the gauge reads only 2% from the Main current. Long story to explain but you can find it in my thread: -► https://forum.ih8mud.com/40-55-series-tech/544543-clusters-gauges-odo-meters-4.html Have a look at page#4 posting#75. Here starts a long discussion about why the gauge doesn't work. In the end there is no solution found.

Rudi
 
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bj40green said:
Save yourself the trouble of diving into this problem.
From Jan. '79 the Ammeter circuit changed. The Gauge changed from 30-0-30 to 50-0-50 and the circuit to measurre this was changed from "Full Current" throug the gauge into a shunt system where the gauge reads only 2% from the Main current. Long story to explain but you can find it in my thread: -► https://forum.ih8mud.com/40-55-series-tech/544543-clusters-gauges-odo-meters-4.html Have a look at page#4 posting#75. Here starts a long discussion about why the gauge doesn't work. In the end there is no solution found.

Rudi
Click to expand...
Thanks for the link. Yes, no use of me trying to figure a fix when it has already been done, 14 ga. shunt 1.5 feet long. Thanks again. Mike
 
bj40green said:
Save yourself the trouble of diving into this problem.
From Jan. '79 the Ammeter circuit changed. The Gauge changed from 30-0-30 to 50-0-50 and the circuit to measurre this was changed from "Full Current" throug the gauge into a shunt system where the gauge reads only 2% from the Main current. Long story to explain but you can find it in my thread: -► https://forum.ih8mud.com/40-55-series-tech/544543-clusters-gauges-odo-meters-4.html Have a look at page#4 posting#75. Here starts a long discussion about why the gauge doesn't work. In the end there is no solution found.

Rudi
Click to expand...

Good post in that other thread. It looks like the FSM shows a fusible link in the earlier meter (posting #74). Where is this link physically located on the truck? I don't see anything under the hood on my '72.
 
The amp meter is protected by two fuses in the versions using the 30-0-30 meters - they's near the firewall on the passenger side (originally wrapped in yellow electrical tape). The fusible link is (or should be) directly connected to the + terminal of the battery then connects to the wiring harness.
 
Ming89FJ62 said:
The amp meter is protected by two fuses in the versions using the 30-0-30 meters - they's near the firewall on the passenger side (originally wrapped in yellow electrical tape). The fusible link is (or should be) directly connected to the + terminal of the battery then connects to the wiring harness.
Click to expand...

I hate to say this but till Dec. 1978 the Ammeter circuit was a 30-0-30 gauge with FULL current through the gauage and no fuses other than a fusible link at the battery post.

From Jan. 1979 the Ammeter circuit is a 50-0-50 gauge that reads the current at a 50:1 ratio. 50 amps through the shunt results in 1Amp through the gauge which is protected by 2x 5Amp fuses.

This what you get when you replace a 30-0-30 gauge for a 50-0-50 gauge. :bang:
DSC00711.JPG
Houston................. we have a problem! Fire in the cluster!

Rudi
DSC00711.JPG
 
bj40green said:
I hate to say this but till Dec. 1978 the Ammeter circuit was a 30-0-30 gauge with FULL current through the gauge
Click to expand...

that's how it was/is in my '72
 
weagle99 said:
Can someone share a picture of this? I have a clip at the postive battery post where the cable connects to the harness but I don't remember seeing a fuse at that location. :confused:
Click to expand...

It doesn't look like a fuse. It's a piece of wire, a few inches long, designed to burn up without causing a fire or sparks.
Looks like this
8852DG18.gif

Have a look here: -► https://forum.ih8mud.com/diesel-tech-24-volts-systems/526232-fusible-link-one-my-78-bj40.html for more info on this subject.

Rudi
8852DG18.gif
 
Ming89FJ62 said:
The amp meter is protected by two fuses in the versions using the 30-0-30 meters - they's near the firewall on the passenger side (originally wrapped in yellow electrical tape). The fusible link is (or should be) directly connected to the + terminal of the battery then connects to the wiring harness.
Click to expand...

I stand corrected. One of my 78 pigs (May 78 build dates) has fuses to the amp meters while the other (Dec 77 build date) does not. Is it possible that the May 78 got the 79 wiring harness a bit on the early side?
 
Ming89FJ62 said:
I stand corrected. One of my 78 pigs (May 78 build dates) has fuses to the amp meters while the other (Dec 77 build date) does not. Is it possible that the May 78 got the 79 wiring harness a bit on the early side?
Click to expand...

Do you mean that you have fuses to the 30-0-30 Ammeter?
Or do you have the 50-0-50 Ammeter?

Rudi
 
bj40green said:
Do you mean that you have fuses to the 30-0-30 Ammeter?
Or do you have the 50-0-50 Ammeter?

Rudi
Click to expand...

The ammeters in the pigs have no markings. I'll take a photo this evening.
 
weagle99 said:
Thanks. I don't remember seeing anything like that under the hood near the battery but I will look again.
Click to expand...

I didn't find one in my truck, either, when I got it
 
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