Ammeter a ticking time bomb?

[VetteVet]

Very nice Richard! I didn't know about the single relay regulator.

Hoseman you have not told us what year truck you are worried about but I doubt that you have anything to worry about if it's a 67 to 72. If the alternator was putting out more than 15 volts it would run very warm and would most probably toast the battery.

[VetteVet]

Originally Posted by Gromit

Great post and very helpful responses and discussion - I'd been worried about this issue too - a couple years ago someone at American Autowire made the passing comment that the updated C10 harness kits modify the ammeter and require a later type voltmeter.. Since I wanted to stay with the Original Equipment style I still chose their "Factory Fit" product but I always remembered the comment and noticed they went to all the trouble to substitute the voltmeter in their updated kit. And face it is a pain to get the different gauge and install it and change the wiring diagram.

Quote:

"I don't recall many problems with them unless the terminals were shorted to ground which could easily cause a fire or a burnt harness."

I'd like to add that while refurbishing my gauge panel I did notice it would be awfully easy to short the terminal studs on the metal backing plate. Because it is a fine line between the 8-12 inch pounds called for as max torque on the terminals - (so risk of overtightening) verses the risk of not tightening them enough - and if they are too loose then the gauge itself can twist just a few degrees and allow or cause the posts to contact the grounded metal backing plate and short out.

I don't have a good photo to show how close the terminals are to the holes in the backing plate but I have the instructions to repro parts that point out the danger of the terminal studs not being lined up properly and a photo of the terminals (although with the trouble spot covered by the washers and nuts - so not much help but hey it gets us in the neighborhood)..

Though I think what I have learned from this thread is so long as everything is installed correctly even if those ammeter gauge posts short out it should only blow one or both of the two small fuses up in front near the grill.

You were posting while I was so I just saw your post.

The comment about the voltmeter in the updated kit from AA is probably true but it shouldn't be hard to do. Instead of two positive wires going to the ammeter , they would have used one positive wire and one from a negative source (ground) to connect to the negative side of the voltmeter.

The positive side can be from a keyed on power source or wired direct from the battery since it uses so little power. The keyed on power sources are right there on the dash cluster on the no 3 pin on the plug or at the fuel gauge or at the temp gauge. Then just ground the negative side of the voltmeter. You wouldn't have to buy a totally different harness just for that.

There are several threads on the forum about converting the ammeter to a voltmeter.

[VetteVet]

Well well well lookie here, the very thread I was thinking about. It's an AA harness kit too.

http://67-72chevytrucks.com/vboard/s...to+a+voltmeter

[Gromit]

Thanks VetteVet I'll bet you have saved a lot of member's trucks from wiring fires over the years of helping everyone here no matter how often we keep asking the exact same questions :-).

I have never understood the part of the wiring diagram that includes the ammeter - but here were the (your) magic words that caused it to finally dawn on me what was going on with that segment of the wiring:

"Instead of two positive wires going to the ammeter "

So that looks obvious to me now but before reading that I had looked at that diagram fifty times and gave up every time after going in hopeless circles.. (I think subconsciously looking for the circuit's drain but not really even understanding that was what I thought was missing).

As far as the risk of the ammeter posts shorting I think I will look for a set of nylon grommets to insulate those terminal posts better from the backing plate and keep my ammeter..(photo attached - maybe something like this)

[davepl]

Originally Posted by RichardJ

Did you increase the load demands at the same time the new alternator was installed?
Was the original 35 Amp Alt unable to keep the battery charged and showing a discharge much of the time?

Yes and no. Yes, there were many increased load demands (fans, pumps, etc) but after cold startup at high idle, there's no real additional load yet (pumps at idle and fans off) so there's lot of extra potential to go back into the battery, and that potential is reflected by the gauge.

If the 35A were retrained it'd go into discharge as soon as the fans came on, particularly if the headlights and hvac were also on. But that's only during load times, it's during "rest/recharge" that I was talking about the gauge pegging.

[Foot Stomper]

This thread is chalked full of both valuable information and experts!
Thanks to everyone who contributed but after rereading it twice, I am still a little confused because I am not comfortable with wiring engineering and I am about to install a Haywire PRO T harness into my 1959 GMC with a full gauge package.

Advice given by Haywire is to replace ammeter with a voltmeter which I do NOT want to do so we discussed this installation (as an option) to put in some added safety.

• Haywire wanted to ensure a fusible link protects the fuse panel while I wanted a circuit breaker for ammeter line as it carries a higher load. Haywire agreed that a circuit breaker used as a terminal block would serve our needs; protecting the fuse panel and ammeter circuit but also recommended the headlight circuit be powered after the circuit breaker.

Am I over thinking-confusing-otherwise screwing this up?

Below is my hand drawn circuit breaker diagram and a copy of the page from Haywire referring to the alternator wiring and am uncertain how to marry the two... any help will be greatly appreciated.

I hope I am not hijacking this thread but hesitated to start another.

[RichardJ]

On your hand drawing, what is the circuit breaker protecting? What is the other side of your Ammeter connected to?

If you read what I posted earlier, there are TWO TYPES of Ammeter gauges. Those with a built-in Shunt and those without.
The 67-72 Truck used a Amp gauge with an External Shunt, BUT,,, BUT they DID NOT use a stand-alone external shunt. They utilized part of the existing wire for the charge circuit to serve two functions. That as charge wire and also as Shunt.
All copper wire has resistance. By selecting that specific section of wire with known length and size, the Ammeter can interpret the voltage drop as the Ammeter reading.

I don't have a '59 wiring diagram and have no idea if your truck had an Ammeter with an internal Shunt or an external Shunt like the '67-72 Truck.

Without an External Shunt meter gauge, all Battery current and charging current from the gen has to into the cab and then back out to the battery. That is what the origin of this thread was all about. Mopar and Jeep used Internal shunt gauges up until about 1980.

If you are using that haywire harness, get a Amp gauge with External, Stand-alone Shunt and install it separately. Stewart Warner and others sell them as Marine gauges

[RichardJ]

To be clear, those gauges I have pictured are considered gauges with built-in shunts. The shunt is mounted on the outside for cooling. 60 Amps would create way too much heat if it was a fully contained unit. The smaller gauge has a Max rating of 20 Amps.
Chevy put a 4 Amp fuse on each of the small wires connection to the shunt, so I would do the same.

[406 Q-ship]

I believe where most of the issues with GM Amp gauges were on the later vehicles like the 70 - 72 Chevelle with the printed circuit boards. Fords knock their gauges down to 6 volts in most cases and chryslers have a weird dohicky on the back of the gauge (possible the shunt as talked about) and both of those systems work well. On the 70-72 Chevelles with gauges, I have yet to see an ampmeter that worked and the printed circuit board wasn't fried. I believe that is where American AutoWire tells everyone to not use the factory Amp gauge and they do not support any external voltage regulators on their update wiring.

My 1974 C10 had an Amp gauges and a burned up circuit board, switched to a volt meter from a later truck and no problems since.

[TBONE1964]

Two thoughts on my end,

There are some (NOT ALL) AAW wiring kits that do not support amp gauges.

If you are using anything over a 60 amp alternator,the amp gauge will not read correctly if there is more than a 60 amp draw.

OK 3 thoughts, Most people for no other reason just prefer to know what voltage is rather than what amp draw is which is why I sell so many volt gauge conversion kits.

And no I have never heard of a fire caused by a defective amp gauge in these trucks. If you pull one from a pre 65, you will notice the back of the gauge face is usually burnt from heat.

Hope you all have a fine New Years.
Tom