Instrument Cluster Installation

[Randy and Easton]

However, I was reading 12 volts at the positive contact where the amp meter plugs in.. wonder if I buy a volt meter and just stick it in there will it read volts even though it has 3 contacts on the back of the gauge and amp meter only has 2? Any ideas y’all?

temp gauge had 4 terminals on the back but cluster only had 3 contacts and it works fine. Any ideas?

 

[AuroraGirl]

However, I was reading 12 volts at the positive contact where the amp meter plugs in.. wonder if I buy a volt meter and just stick it in there will it read volts even though it has 3 contacts on the back of the gauge and amp meter only has 2? Any ideas y’all?

temp gauge had 4 terminals on the back but cluster only had 3 contacts and it works fine. Any ideas?

No. The amp gauge is wired to have the full amperage of the truck flow through, the voltage gauge needs a ground and a positive

 

[Randy and Easton]

@AuroraGirl , so with my volt meter reading 12 volts on the positive contact in cluster putting a volt meter gauge in instead of amp meter won’t work?

 

[Randy and Easton]

Well, I see what you’re saying. I think I will order the new amp gauge and call it done! Only way I get 12V is positive contact in cluster and chassis ground. Thanks @AuroraGirl

 

[WFO]

As long as it's not a high output alternator, I'd rather have an Amp Gauge.
If you're headed out of town and your alternator goes out, with a Voltage Meter you wont know this until the battery begins to drain.
An Ammeter will show a discharge immediately, giving you time to get back home or to an Auto Parts store.

 

[Snoots]

Take that Amp Gauge out and throw it away! Get a stock Volt Meter and put one lead to ground and the other to a 'Run' or 'Ignition' spot on the fuse box.
Those Amp Gauges cause electrical fires.

 

[Randy and Easton]

@Snoots , yeah but with the cluster powered by the circuit board and the volt gauge attached to the pins in cluster that are powered which holds it in place. Hate to doctor it up and mess up circuit board and maybe other gauges. Everything is actually working well at this point. Going easy on this one but I absolutely see your point about amps running “ through” gauge and the potential…

 

[Ellie Niner]

Okay, I'll throw my bit in here, as I have worked with both the 73-75 ammeter and the 76-up voltmeter. You *can* get the ammeter to work, and work safely, but it's usually really time consuming to make one display what your charging system is doing somewhat accurately; they tend to only twitch the needle a tiny bit one direction or the other out of the box. These are a shunted ammeter, so only a tiny bit of the current flowing through the electrical system passes through the ammeter, while the rest bypasses it and travels trough the main wiring harness. -i.e. let's just use 100 amps as a nice, round figure... 1 amp will travel through the ammeter while the other 99 pass through the main wiring harness. In reality, full scale on these ammeters is usually about 60 amps. By the way, you can flick that ammeter needle around so the pointer sticks up instead of down.

It looks like you started out with a voltmeter cluster, and are planning on installing the different cluster with an ammeter? Did you get the ammeter harness from the donor vehicle, or install a new one? That will have two rubber fuse holders containing those little stubby SFE 4 amp fuses, one on each side of the ammeter circuit... those are a must.

A voltmeter can be installed, and wired off of the temperature gauge... the voltmeter only uses two of its three terminals, though one of them (the ground) is on top instead of being arranged side by side like in your ammeter cluster. If going that route though, it might be easiest to just score a cluster and printed circuit that are already set up for a voltmeter.

 

[75gmck25]

Read Ellie Miner’s post carefully - the shunted ammeter design in the Squarebody does not send the entire current flow through the dash, and it is not dangerous. It also has two small fuses in the wiring harness under the hood to protect it. However, it is measuring the voltage from two different points in the wiring harness and using that to mechanically “calculate” the current flow.

The accuracy of a shunted ammeter depends on the shunt being a known resistance value, and then measuring the small voltage change on each side of the shunt. However, the squarebody resistance will change as the wiring harness gets old. Overall, the voltmeter will be more useful.

I converted my truck from ammeter to voltmeter, using a new voltmeter from LMC. It’s a simple conversion, but I couldn’t point you to the internet article I found and used.

 

[Randy and Easton]

@Ellie Niner and @75gmck25 i have found the internet link to do the conversion but decided it’s too much work at this point. Cluster came in original truck with amp meter and when I tried to test gauge out of truck I did not put it in line correctly so I think I cooked it. I’m just going to put a new one in there and be done.

You guys are absolute rock stars and if I had to do it over and cluster was in closet and I had nothing to do I would switch it to a voltmeter. Someone said they thought Chevy went to voltmeters on 1976 and later, so don’t know why this one has amp gauge? Sum of many owners…

Thanks y’all. I’ll report back when new amp gauge is installed

Randy and E

 

[Ellie Niner]

@Randy De Oreo All of the 1976 trucks I've seen have a voltmeter, though I wouldn't be super surprised to find out that a few squeaked out of some assembly plant with an ammeter early in the year or something like that. My 1975 GMC heavy 3/4 ton came out of the Fremont plant wearing Sierra Grande 15 emblems on the front fenders (should be 25 on a GMC).

There's also a holy gawd number of IC variations over the 19 model year run, so it's not uncommon to see single gauge swaps to complete Frankenclusters... I've sorta wanted a tach for mine, though I like my clock and don't want to lose the Brake idiot light with a tach/fuel combo... a vacuum gauge would be cool too. Too many decisions!

You are seeing +12 volts at both terminals for the ammeter, yes? If one is grounded, you'll probably pop the new gauge... More common to have one open circuit due to a blown inline fuse.

 

[Randy and Easton]

@Ellie Niner , no. Right contact is 12v with meter grounded to firewall. If I use both contacts in the cluster meter shows nothing.

 

[Ken B]

trying to finesse the cluster in is like a square peg in a round hole , and the peg is 45 year old plastic.....fragile
I can get all but drivers door side in flush but it is way out. and that tab has already been repaired

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[AuroraGirl]

trying to finesse the cluster in is like a square peg in a round hole , and the peg is 45 year old plastic.....fragile
I can get all but drivers door side in flush but it is way out. and that tab has already been repaired

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If the rest of the cluster fits nice and tight, then you have a few options. Bend the tabs to allow it to sit in further or make a spacer of sorts for that one , and use a longer screw if needed. I would do that since a small stackof washers can find you how large it needs to be,then cut a piece of plastic or a sleeve of metal down to that and install.