I've traced both clusters and have made up two diagrams of the plug wiring.
 The first shows the original 1969 Full size Pontiac standard instrument cluster configuration, with the Rally cluster to the right. The Rallys wiring is likely unique to the USA car, athough it is possible Canadian Cars with the Rally cluster (was there any?)may have had a similar schematic.
The second shows how the old plug should be configured to work on the rally cluster. Remember, it's not been tested. So use your own judgement.

As you can see, some pins stay the same, and the conversion really doesn't require big changes in wiring, only some changing of pin positions in the original plug. You'd probably be wise to fab some sort of tool that can easily unfasten the pins from the cluster plug.

I've not done any research on wiring up the Ammeter, as I won't bother as I'm going with a 12SI Internally regulated alternator and will add a voltmeter, but I'm sure it could be done no problem. Just make sure you use the correct gauge of wire. The Ammeter wires on the Rally cluster are fairly heavy.

I feel that one could just use the exsisting wires to the old temperature and oil pressure switches on the new temp and pressure senders. So in that manner, no wires would have to be added through the firewall (other than the ammeter if required).

Wow! Where were you when I converted my 66 Grande Parisienne to the US gauge cluster???!!! That sure would have been a help. You make it look like it will be pretty easy with that.

Thanks for taking the time to create this posting Mark! Todd

very nice to have friends, to provide such detailed help ..  good work Mark!! 

 Glad I could help.
 Never seen anything posted anywhere describing these changes.

 I wish I could convert the ammeter to a voltmeter, and have the face re-stenciled accordingly. Someone somewhere probably does it, but at a cost probably not worth it.

 Going to a wrecking yard in Stratford this weekend, I plan on keeping my eyes open for some sort of GM cluster with a voltmeter. Who knows, with a little effort, I could probably figure something out myself.

Cheers, Mark.

Mark, do you think the Canadian Pontiac harness is the same as Impala?

 I have no idea Todd.

I put an internally regulated 3 wire alternator on my 62 Parisienne in place of the generator when I swapped a 283 for the 261. I followed a Chevy wiring diagram for a car without an ammeter. It works - charges 14+ volts under load, but the factory ammeter doesn't read properly, plus I think I'm getting a drain on the battery. Does anyone have a wiring guide for putting this alternator on a Pontiac with built in ammeter. I'm worried that the ammeter circuit is not up to handling the load of the alternator system. I'm willing to bypass the ammeter but I think I still need a resistor in the system to make it all work off the key?? Any advice and/or wiring diagrams  for this swap would be appreciated.

Mark Do you have knowledge of anyone who has done this conversion on a 67 or 68? Am I right that 67 and 68 use the same cluster? From what I can find, it seems that they do. There is a reason for me asking.........!!!

Carl,
 
I have no knowlege of the conversion on a 67-67.
Although the 67-68 big pontiac cluster looks almost identical to the 69-70 from the front, I believe it's different in the back, in the plug and circuit board.
It likely would share a similar wiring design out to the senders as a 69, and it would be no big deal to trace it out comparing it to the original cluster.

What are you doing?

Cheers, Mark.

PM sent.

Hi Carl do you remember how you did the conversion to the US gauge cluster?
I've always had my eye on doing that if I could find one. It a nice subtle modification that no one would notice except me and a few old guys.

ken

As I recall, I just snipped the plug off and circuit tested to figure out each wire. It was very time consuming changing printed circuit to individual wires. I never did get the oil gauge to work correctly.

Dave, there is a thread about this in the 65-70 full size section with details but it has no diagram in it. Would you mind if I merge this into that thread? They would go very well together.

Sure, please do, I'd like to see it as well!

What book is that diagram from? Any idea what the CSI means in the top 2 drawings? ie: CSI Battery & Charge Circuits - All Except Pontiac with Rally Gage and CSI Battery & Charge Circuits - Pontiac with Rally Gage.

There we go, all the info in one thread now.