Last 3 Gauges

[ChevyMan90]

I did a LQ9/4L60E swap in my 1999 C1500 OBS. I have my water temp, oil pressure and voltmeter gauges working. I just need my speedometer, tach and fuel gauge to work now. I have downloaded and printed all the wiring diagrams/connector end views from lt1swap.com and some from All Data. Im using a new standalone wiring harness and it has a lead for tachometer signal output and a lead for the vehicle speed signal. Where should I connect the wires coming from my new LS harness to the existing wires to get power to my gauges? I see several Pins on the 4 VCM Connectors that say Vehicle Speed Output. Also I have a diagram for the C100 connector that goes into the firewall on the drivers side. Does the tach get its signal from here? Looks like it will be a white wire, either connector B2 or E8? Lastly theres the fuel gauge. If anyone can give me some help on where I should start I would greatly appreciate it. Thanks!

[ChevyMan90]

Well I got my speedometer working. 2 more to go.. Any help on the tach and fuel gauge? Thanks

[crzy8mnky]

How much of your old harness have you removed? The tach signal comes from a white wire on a three wire plug that goes into the coil. The fuel gauge signal is a purple wire that comes from the computer.

[gagliano7]

The tach wire is the white one that was hooked to your distributor. You may have to make changes in the tune for the tach to work.

[ChevyMan90]

My entire old harness is still in my truck, along with my new harness working all of the engine/trans functions. I haven't removed or cut any old wires yet. Once I get these last 2 gauges working I can start getting rid of wires I don't need and clean up the engine bay. I have not had a chance to work on the tach and fuel gauge but today I will be looking into it. Can anyone confirm where the tach signal comes from on a 96+ Vortec motor? The coil or the distributor? Thanks for helping be narrow it down.

[crzy8mnky]

If you connect the white wires of the coil and the ignition module and then pull the tach signal wire from the old engine connector into the new connector you will have a tach signal. IIRC the only plug going into the distributor on the Vortec 5.7 is the camshaft position sensor. On the TBIs the ignition module is under the distributor cap, however on the Vortecs its on the passenger side of the intake manifold.

[ChevyMan90]

1 more to go! Got my tach working. It looks to be reading about 1/2 of what it should be. Have to look at the tune and make adjustments.
So last one is the fuel gauge. Here is what I know about this...

I read on LT1swap that on the LS PCM on C2 (Red Connector) you add a pin in slot 38 - ADD PIN FOR PWM FUEL GAUGE SIGNAL OUTPUT (used to run factory fuel level gauge in 96-99 trucks).

54 - is a Purple wire and named Fuel Level Sensor Signal


On the 4 connectors that went to the OLD Vortec PCM there are two wires that deal with fuel level. They are:

C3 (Clear) - PIN 13 is a Purple/White wire labeled Fuel Level Sensor Signal
C1 (Blue) - PIN 9 is a Purple wire labeled Fuel Level Output

Which of these wires are needed for my gauge to work? Thank you all for the help, looking forward to getting my last gauge working so that I can get rid of all these unused wires!

[Blasphemy]

I believe the ppl/wht white goes to the factory PCM and the solid purple goes to the gauge. Check your firewall connector to verify. Were you able to find the pinout descriptions for your old 5.7 PCM? They're pretty helpful and a wiring diagram of your dash is usually pretty easy to find also.