I installed a FAST 2.0 multi port FI system on my 87 Trans Am. Needless to say the wiring was a disaster. Basically everything ECM related was removed. I have a digital dash and now my gauges won’t work. Tach is either flaky or wont work at all. Even fuel gauges won’t work. Did I remove something I shouldn’t have? Does anyone know where I can find a wiring diagram for a digital dash?

 

We have no idea what you've physically done, so how can ANYONE know whether you "shouldn't have"?

The factory service manuals are a good place to get the diagrams. I get mine off ebay

 

My implied question was is the instrument panel tied to the ECM in any way? To my recollection it isn’t, but maybe I overlooked something? For instance on previous 80s GM cars I’ve owned with analogue gauges the coolant temp runs to the sensor on the driver’s side head. Mine does too but it’s not reading correctly. If I ground the wire the gauge pegs at 260 which is what it should do with analogue gauges. With digital dash cars does that tie into the ECM somehow? Or is my CTS just bad?

 

Most pre 88 Thirdgens you can remove the ECM harness completely without affecting the gauges in any significant way. ( If the car is an automatic you WILL loose TCC lock up ! ) However; with electric speedo cars there is at least 1 conflict; The VSS buffer ground for the Speedo system is located in the ECM harness. This is a "map" of the C207 Connector for 87 & it shows that PIN 'M' is the ground for the VSS Buffer. C207 is the 2 Dash harness -to- ECM harness plugs under the pass side of the dash. You might get the speedo to work again if you splice/jump a ground to PIN 'M'.


1986 & 1987 C207 ( TPI )

PIN Color From / To (Notes)
A Brn ALDL / ECM (AIR control)
B Red ALDL / Fuel Relay ( TPI )
C Brn/Wht ECM / CE Light ( TPI )
D Tan/Wht Fuel Relay / Fuel Pump ( TPI )
E Wht/Blk ALDL / ECM (test)
F Pnk/Blk IGN fuse / EGR-ECM
G Pnk/Blk Gage Fuse / Burn Off Relay ( TPI )
H Tan/Blk ALDL / TCC-ECM
J Org ALDL / ECM ( TPI )
K Brn ECM / Speed Buffer
L Tan/Wht Fuel Relay / Fuel Pump ( L69 )
M Blk/Wht VSS,P/N switch / Grd
N Org/Blk ECM / P/N switch
P Ppl Brake / TCC
R Ppl/Wht Crank Fuse / Cold Start-ECM ( V6 )


** Many (all?) TPI cars have the oil pressure wire running off the sending unit, into the ECM harness, thru a 2 wire connector that connects to the ENGINE harness, then in thru C100 to the dash. You might need to splice a new wire off that 2 wire plug ( TAN wire is Oil Pressure ) on the ENGINE harness directly to the sending unit to get your oil pressure gauge working.

Pretty sure all your other gauges are going to be run thru C100 on the drivers side of the Firewall. This schematic is from the 87 Firebird Service manual.

 

Thanks! I have seen this pin out diagram before. For my oil pressure, there is a tan wire coming out of C100 but then it goes to one end of a plug and the other terminal has a green wire coming out. The plug is open with nothing connected and is relatively close to the power brake booster. It’s not the kind of plug the oil sending unit uses and it would never reach it. I have no idea what this is for. Is the wire for the oil pressure gauge tied into the oil pressure sensor that’s right above the oil filter?

 

I think your looking at the correct plug; Pretty sure the TAN wire is the Oil pressure wire and the GREEN wire is for AC signal.

That 2 wire plug would have plugged into the ECM harness and the ECM harness would have had a single TAN wire sticking out of it near the Oil Pressure sending unit; on the 87 the stock Oil Sending unit is the one behind the Intake and next to the distributor. (The stock sensor above the oil filter on your 87 is JUST for fuel cut-off.) In order to get the oil pressure working again ( the cheapest option ) is to simply splice a terminal at the end of a wire, plug it into the original oil pressure sending unit, (behind the intake) then run the wire to that 2-wire plug and tap/splice it into the TAN wire.

Because you've GOT to splice and modify anyway this is what I would recommend: (I didn't like dealing with the original oil pressure sending unit behind the intake on my 88' so I converted mine as described here. )

Buy this sending unit: Part Number PS228
https://www.ebay.com/itm/193452180937

Buy this plug:
https://www.ebay.com/itm/323576581309

This sending unit is for 90-92 Camaros, it's a 3-wire sending unit and the oil pressure wire gets connected to it. Remove the sending unit above the oil filter and install the replacement sending unit. Remove the 2 pins from the factory plug and install them in the same location in the replacement plug. ( you can cut/splice but re-pinning is better IMO !) The third wire from the replacement plug is your new Oil Pressure sending unit wire, splice a piece of wire to it and tap/splice into the ENGINE harness 2-wire plug's TAN wire. The "canister" type sending unit behind the intake is no longer your oil pressure sending unit, the replacement sending unit above the filter is. You can just leave the canister type sending unit in place,..... or remove it and install a plug in the block.

 

That would make sense why I can’t find any tan wire going to the sending unit! I removed the original ECM harness! Thanks!

 

This is the plug I’m referring to.

 

About 97% sure that's it,... plug 'C111'. TAN goes to Oil Pressure sending unit & GREEN wire is AC signal to the ECM.

 

I would recommend purchasing what "John in RI" Posted.
That AfterMarket Pig-Tail should be far less expensive than a GM/ ACDelco/ Delphi Pig-Tail.

I just wanted to add some GM/ ACDelco/ Delphi Part-Numbers for anyone looking for the information.

The Pig-Tail for Oil-Pressure Safety-Switch/ Sending-Unit are:
-GM Part-Numbers= 12085499, 88862243.
-ACDelco Part-Numbers= PT121, PT2324.

The Components/ Parts for anyone that builds their own (All Delphi Part-Numbers):
-Body= 12065401
-TPA= 12066176
-Seals= 15324976 (Three Required).
-Terminals= 12048074 (Three Required).

The Electrical Connector Pieces/ Parts add up to less than $4.00...
That might be incentive enough, for some of you to learn how to assemble/ disassemble some of the Delphi Electrical Connector Systems.

 

Thanks guys. I just ran a new wire from the sending unit by the distributor to the tan wire and spliced it in. I don’t have AC anymore so idgaf about the plug or the green wire. But now the oil pressure indicator is visible but it’s like all the gauges are dead. Oil pressure reads zero, voltage is all the way down, temp is pegged at 260 and the tach doesn’t work.

 

Check Fuses.

 

Also, when I turn the lights on (running or headlights) the gauge indicators, tach, and speedo digits disappear. I’m at a complete loss. I’m still going to look for that ground at the C207 connector. Maybe that’s the problem.

 

I had just went through this on my 86 Iroc (for months trying to find the correct info). Same plug, same place. I spliced the tan wire and ran over to the oil sender (bell style) behind the dizzy, put a spade on the end of the wire and called it good. I did use the green for my a/c also, but since I'm using a Holley HP ECU, this was for my new ECU wiring set up controlled by it. Also, the C207 plug left from the factory ECM had some useful wires left for me to use. While going through that (John in RI) had an accurate pinout of my year for both plugs there, that contained a ground I believe was for the gauges that went to the ecm which was no longer there, so I had to ground that, along with using a fuel pump wire and switched accessory wire for my new ecu. So definitely get the correct pinout (the plug itself is lettered for each pin) and verify it's the right one, and check for that. You should be all set after that. Actually, now that I remember it more, John had ALL the years broke down on those pinouts, grouped by the years that were the same, very detailed - that's what I would search for. (Thanks John in R I !!!)

 

Always welcome !!

 

It was that d damn ground at M! Now I just gotta calibrate my speedo! Thanks man!