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Discussion Starter #1 (Edited)
I bought a 73 or 74 Grand Prix gauge cluster for my Phoenix. I was pleased to learn that a 73-77 Grand Prix cluster is basically the same design as the 77-79 Phoenix cluster! It should "bolt right in" with some minor wiring modifications & new sending units. If this works it will give me oil pressure, water temp, volts and tach all in the dash! Plus 120 MPH speedometer and no PRNDL which I no longer need!:) That's the good news... But there are questions about the tach...

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I am almost certain it is from a pre-HEI car as they just started with HEI in mid-74 as far as I know. As I understand the pre-HEI tachs won't work with HEI unless you use a tach filter or tach adaptor. Here are 2 links to filter/adaptors. Can anyone tell me if either one is what I need to make this work? If not what do I need to to make this work?

http://www.summitracing.com/parts/sum-850511/media/instructions

http://http://www.glowshiftdirect.com/hei-tachometer-signal-filter.aspx?gclid=COOB8b2l_7MCFcqY4AodABEAjg
 

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Try the install without any filters, my 72 Chevelle was converted to electronic ignition and the factory tach worked fine. IIRC it is the MSD system that does NOT play well with tachometers.
Congrats on the cluster, that is going to look real sharp in your dash.
 

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Discussion Starter #3 (Edited)
Try the install without any filters, my 72 Chevelle was converted to electronic ignition and the factory tach worked fine. IIRC it is the MSD system that does play well with tachometers.
Congrats on the cluster, that is going to look real sharp in your dash.
Thanks Philip! I'm pretty excited about this because a couple years ago I was trying to figure out how to put an in-dash tach in and got nowhere. Recently in dealing with speedometer (or cable) issues I discovered just by observation that the 73-77 Grand Prix, 75-77 Grand LeMans, 73-75 Grand Am and 77 Can Am all use the same basic cluster as the 77-79 Phoenix. PHOENIX GUYS TAKE NOTICE!!:yes:

I just had another guy tell me he has used a 73 Pontiac tach in his 77 Trans Am with HEI without any filters and it has worked fine for 6 years. He said the ones that were the problems were the single transistor/capacitor ones from the sixties and early 70's. It's a relief hearing you've had the same experience. I'll hook it up the same as the current Sun tach.:)

I can't wait... but I'll have to as we have sold our house and are moving in mid-Jan.:eek: The move is local--7 miles away but still a lot of time and work. As it is I haven't been able to work on the car for a few weeks. So I won't be able to do this till Feb!
 

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February :mad: unacceptable I can not wait that long :rolleyes:
J/K hope the move goes well. I considered moving until I looked around at all of the stuff we have...we will just stay here a bit longer.
 

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Nice find on the cluster! I agree with Philip ... the tach will likely work okay with HEI without adding a filter.

I swapped my 72 C10 over to HEI and also added a factory tach (out of an old farm truck). It works just fine without a filter.

GM did use inline filters on many factory tachs but I believe those were primarily to cut down on radio interference. The circuit inside is different, but they look like the capacitors (condensers) that are often used inline with the heater blower motor; also to reduce radio interference.
 

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Discussion Starter #6
February :mad: unacceptable I can not wait that long :rolleyes:
J/K hope the move goes well. I considered moving until I looked around at all of the stuff we have...we will just stay here a bit longer.
I'm looking forward to the move...just not the mov ing! One thing about my new garage is that it will be a little smaller but I will also have a shed where I can put a lot of the stuff that clutters my garage--like lawn mower and snowblower (but you have probably forgotten what those are! :D). So hopefully overall it will be better.
 

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Discussion Starter #7
Nice find on the cluster! I agree with Philip ... the tach will likely work okay with HEI without adding a filter.

I swapped my 72 C10 over to HEI and also added a factory tach (out of an old farm truck). It works just fine without a filter.

GM did use inline filters on many factory tachs but I believe those were primarily to cut down on radio interference. The circuit inside is different, but they look like the capacitors (condensers) that are often used inline with the heater blower motor; also to reduce radio interference.
Thanks Ray! I could not find any information on how to get a factory tach in a Phoenix. Phoenix are fairly scarce plus not many people bother with them. So it's hard to get info on the Pontiac-specific components and any ideas on modifications. I happened to be looking at a Grand Prix dash and realized it was the same cluster layout as mine! I'll just hook it up and see how it goes. Assuming I hook it up right, do you think there is any way I can hurt it if it ends up not working for some reason?
 

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Discussion Starter #8 (Edited)
Well I am finally going to be able to start converting over to
in- dash tach and gauges from a 74 Grand Prix. Here are the 2 different gauge clusters.

Current Cluster- FRONT



New Cluster -FRONT



Current Cluster-BACK




New Cluster-BACK



The New cluster didn't come with the correct printed circuit so I'm thinking of trying to use the the back plastic housing and printed circuit from my current cluster even though the housings are somewhat different.

QUESTIONS:

1) In the center of each cluster are the gas gauge, oil, water temp, and volt indicators. (Current has warning lights-new has all gauges). It looks like I would need to drill holes through my current plastic housing so the gauge terminals can come through. Each gauge in the new cluster has 2 terminals (see picture) This brings up a question...The 3 warning lights in current cluster each only have 1 wire goung to them, not 2. But the gas gauge (upper right) does have 2. (see current cluster- BACK picture).



Is there a common ground in the printed circuit eliminating the need for a second wire to each warning light? Is that ground supplied through the warning light sockets? If so,how would I wire these new (see directly above)since they have no warning light to supply a ground?

2) In lower right (see new cluster-back) there are 3 terminals for the tach...ground, coil and 12V. I assume I can hook the tach up directly just like my current Sun tach without the need for any printed circuit right? The lighting for the tach would be from a light socket fed from the current printed circuit.

3) When I disassemble each gauge cluster is there anything I especially need to be careful about? (Never done this)

Appreciate any advice or input!
 

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Kim IMO you may need to hard wire the new cluster to have it work correctly. In the Nova the wires in the connector are in different locations and the printed circuits are different between the standard and gauge cluster.
it is not that hard to do, just very time consuming.
The bulbs that are for illumination have a ground, but the lights for oil, gen, water temp and brake warning lights do not, they are part of a circuit with the ground being provided by a sensor or other device. Same will be true for the instruments that replace those lamps.
Wish you were closer, I could lend a hand with the wiring.

Here is a shot of what I did to mine

 

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Discussion Starter #10
So just use the whole new cluster, housing and all and eliminate the printed circuit? Do you think I should start by trying to find a 74 Grand Prix schematic for the gauge cluster and a schematic for the 79 Phoenix gauges (although I assume the wire colors may be the same as a Nova). If I could identify the wires from both cars I could figure out how to hook up my stock harness.

Philip,is the wiring harness in your picture a modified version of the stock harness or aftermarket?
 

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Discussion Starter #11
Another Question

I have pdf's of wiring diagrams for 77-78 Nova but they stop at the "Printed Circuit Connector" Is there a diagram that shows the specifics for the gauge cluster itself? What I mean is a diagram that shows where the different colred wires ultimately connect to after they connect with the printed circuit. (like Dark Blue goes to oil pressure, Pink goes to gas gauge, etc.) OR do you just have to trace everything back from the printed circuit to see where it originated? :confused:
 

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Kim the schematics will all stop at the plug. The wiring in my photo was created by me one wire at a time. After it was done it was tied together neatly. The stock harness plug wires were used with a new plug to match the one on the cluster for ease of installation. Where possible I used the factory color and wire gauge to make any troubleshooting needed in the future easier.
 

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Discussion Starter #13
Okay, thanks Philip. By the way I DO wish you lived closer--I would welcome your help with this wiring!:D I see Auto Meter logos in your picture. Is that where you got the plug and connectors to make the harness? Is the plug specific to 4th Gen Novas or is it a mult-application plug? I'm working on getting a wiring diagram for a 74 Grand Prix but maybe I don't even need one if I make my own. What do you think?
 

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Looks to me (without measuring and tracing circuits myself) like you could use your original printed circuit again.

The posts you are worried about should just press into some clips that electrically connect and physically hold the printed circuit in place. Those used by your original cluster are probably the same as the ones used for the GP.

Unless you find a good printed circuit for the GP cluster, to me it would just be a matter of drawing out a schematic of the printed circuit you have to see if it will work and repurposing some of the wires via re-pinning the connector.
 

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For instance, the fuel gauge is in the same spot, so the original wire for it shouldn't have to be changed.

The alternator light in your original cluster is where the voltmeter is in your new one. Your new cluster appears to have an alt/gen light at the bottom of the speedo, so the command wire for it would have to be moved over.

It all depends on the schematic of the printed circuit and if you can find a circuit for the GP cluster, I bet it would be close to plug and play.
 

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It's all I could find very easily at all. But for a new circuit and factory appearance for those who care to look, maybe worth it.
That is true. I have repaired printed circuits with some success but there were several that were deemed "learning experiences" and became unusable :yes: If the reproduction is well made it would be worth the money.
 
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