Ok so brief details on car:
1986 IROC
350 CID engine with 700r4 trans

The gauge cluster that was in it when I purchased the car was the 145MPH cluster with the 4 small gauges in the middle. This gauge cluster appeared to be completely computer controlled so it had to go since obviously there is no ECM anymore. I purchased another cluster from the thirdgenranch site that had the mechanical speedo in it and had the 3 gauges in the middle. My mechanic is now telling me that the wire connectors do not match for any of the gauges so the only thing that works is the speedo. I am at a complete loss as I figured the connectors would be the same. Is there any insight that anyone can provide on this issue? I really do not want to drop a lot of money on a auto meter gauge cluster or digital dakota.

 

The best 'direct fit' replacement cluster for your IROC could come from any 85-89 V8 Camaro !

ANY factory speedometer HEAD (only) will fit into any other factory 82-89 cluster and work properly.

ANY factory 82-89 stock gauge cluster should plug directly into your 1986 Dash cluster plugs - if they are still factory assembled. The 86 IROC would have a factory 'gauge' cluster stock so all the gauge wiring should already be in place in your dash harness and engine harness.

A stock Tachometer is made specifically for a V6 or V8,... If a V6 tachometer is connected to a V8 engine the readings will be WAY off.

If you attempt to install a complete 82-84 Speedo cluster there IS a wiring change that will cause back-lighting problem and a BRAKE warning light problems. The BRAKE warning indicator was moved from one side to the other side starting in 85.

The 'computer' ( It's an ECM ) doesn't control your cluster in ANY WAY. The entire 'computer' and it's complete wiring harness can be removed from your 86 and the cluster will continue to function properly. ( you will lose torque converter lock-up by deleting the ECM. )

Seems as if a "custom" cluster was installed, and if so than it's very possible that the factory wiring was altered at that time. You will need to verify that all the wiring is still properly connected at the cluster plugs,... AND at the various sensor connections under the hood.

Here is the diagram showing the Printed circuit connections at the back of all 1986 IROC clusters.




Good Luck !

 

If you swapped out the engine you would need to use the sending units off of the original engine that came off of the car (Ie. temp and oil) so that they match what the cluster needs to operate correctly. If you do not have the original engine then you would need to acquire the correct sending units for the gauges to work.
The temp sensor is located on the drivers side between the first and second spark plug (#76 in image below).
The oil sensor is typically located by the distributor also on the drivers side (#78 in image below).


The original cluster should work and the wiring to the engine should be correct, -that is unless (as mentioned) they were modified. The only thing that would have changed as per the previous thread you posted is the 350 that was installed. And that probably did not come with the correct sending units which is probably why the cluster doesn't work.

To clear things up:
Mechanical gauges use tubing that the actual fluid travels through, then when the fluid reaches the gauge, the gauge responds mechanically to either the pressure or the temperature.
This is an example of a mechanical temp gauge (explains how it works within the first 30 seconds, -gas expands which pushes the needle):

Electrical sending units sense either temp or oil pressure at the engine. Then the electrical signal is sent through the wire to the gauge. However, you need the correct sending unit for the stock gauges to work.

As mentioned, there is no computer interface to the cluster. New technology does, older 1986 technology does not. The transmission speed is sent to the cluster mechanically via a cable and a signal is created at the speedometer via a sensor which had three wires to a yellow connector, this electrical signal is then sent to the ecm(Computer) and/or the cruise control. It's from the cluster to the computer not from the computer to the cluster.
The back of the cluster looks like this:


Your cluster should look like this from the front, I'm not sure how you would have four gauges in the middle.

 

That diagram will help TONS. I believe that the previous owner purchased the 90-92 gauge cluster and stuck it in there. It appeared to be completely electronic and looking at pictures online that would be the gauges.

The one that I ordered from thirdgenranch is like the one posted above so at least now I am on the right track.

So if I am understanding correctly I should only need the original sending units for the Temp, Oil Pressure, and fuel I am assuming. The voltage should pull from the alternator and the tach should receive the signal from the distributor.

Do you guys think there will need to be certain current/resistance also for the readings from the alternator and the distributor?

With that diagram I am hoping I can wire this all in together it does not seem too difficult to get my cluster working again.

 

Similar but, not the same.

Technically, the replacement (older) gauge sending units should be fine. Seems having the wrong gauge cluster is your biggest problem.

 

Oh, that makes sense now. The back side of the two different clusters are completely different physically, and the speedo on the later is electronic. So yes completely incompatible.
Can you post pics of your dash as it sits now?

 

I now have the one that is posted by you Scorpner. The one that was sitting there originally was the one posted by Deadbird. When I figured out that was the wrong cluster I ordered the correct one for the 86. The car was bought as a rolling chasis so I am assuming the previous guy just bought one from the junkyard and stuck it in.

The sending units that are currently in the 350 are definitely not from a Camaro so I will look into getting those.