Truck Side wiring

[Wagonbacker9]

Does anyone know of a good resource for what connections are needed on the truck side to keep various things working? I'm specifically concerned with my 1993, but if theres a good listing somewhere that would be excellent. I'm fully prepping my engine side harness prior to going in, and would like to keep the downtime minimal, so knowing what connections I'm looking to make on the truck side ahead of time would save time.

Things I'm aware of in my research thus far:

Oil pressure sensor to keep fuel pump running (and gauge)
coolant temp sensor (gauge)
AC signal wire to bump up idle

etc

[Clayman]

Tachometer has to be hooked but youll have to tell nelson or who ever tunes it the model of your truck and theyll tune the pulse so it will register right.
Vss also has to be connected and you can either feed the guage thru the drac box or you can use the speedometer output wire from the new harness and do it that way. Check out the obs to lsx conversion thread... redheartbeat has some good info about speedometer wiring. If you have any other questions just ask... were here to *try* to help!

[Clayman]

Btw that thread is a sticky if youve never looked at it. Itll be at the top of the lsx conversion page.

[Wagonbacker9]

Tachometer has to be hooked but youll have to tell nelson or who ever tunes it the model of your truck and theyll tune the pulse so it will register right.
Vss also has to be connected and you can either feed the guage thru the drac box or you can use the speedometer output wire from the new harness and do it that way. Check out the obs to lsx conversion thread... redheartbeat has some good info about speedometer wiring. If you have any other questions just ask... were here to *try* to help!

I'm doing my own tuning, and the speedo is just one of many concerns, but I do thank you for your input. I have read through the sticky, and just about every other resource I can track down. I feel pretty solid on most of the other stuff:

1" setback mounts needed to maintain current drivetrain position
using the pump/regulator out of the GTO for the truck after I upgrade the GTO assembly, returnless.
Wiring harness mods to be made based on info off LT1swap.com
HPTuners to flash in the correct tune, delete trouble codes, remove VATS etc

The only stuff I'm really not solid on thus far is what connections need to be made truck side, and ideally, what wires in what locations and colors they are.

[Wagonbacker9]

So here is what I've found. These are the pins on the LS ECU (99-02) that need to be connected to the truck:

Switched power can be sourced from the red wire at the ignition coil.

C1 BLUE
19 PCM IGN Supply (12+ switched)
20 PCM Battery Supply (12+ constant)
33 TCC Brake switch - connect to purple wire on brake pedal (12v normally closed switch)
42 Fan 1 Relay Ground
57 PCM Battery Supply (12+ constant)
58 Serial Data to OBD2 Port
71 Tow/Haul Mode switch (Momentary Ground)
75 PCM IGN Supply (12+ switched)

C2 RED
9 Fuel Pump Relay Control Connects to green/white tracer
10 Tach output signal [connects to white wire behind cluster?]
16 4WD Low signal (only used if VSS on Tcase Output)
33 Fan 2 Relay ground
38 Fuel gauge output (runs level gauge on 96-99 trucks)
46 CEL signal wire
50 VSS output [connect to light blue wire with black stripe and red wire with white stripe in DRAC box?]

So... I beleive the ones in bold are the only ones I'm not fairly confident of what to do with. I'm fairly confident that the rest will be fairly easy to figure out.


NOTE: This pinout ignores EVAP, rear O2s, AC, and probably a few others some people may care about but I tried to make this not just dedicated to my swap, as I've found the info out there for where to actually hook this stuff up seriously lacking (compared to all of the other topics).

Also, I see nothing in the factory harness info I found for oil pressure... this surprised me. Wouldn't it be wise of a MFR to have a low oil pressure safety built into the ECU?

[greenvortec]

So here is what I've found. These are the pins on the LS ECU (99-02) that need to be connected to the truck:

C1 BLUE
19 PCM IGN Supply (12+ switched)
20 PCM Battery Supply (12+ constant)
33 TCC Brake switch
42 Fan 1 Relay Ground
57 PCM Battery Supply (12+ constant)
58 Serial Data to OBD2 Port
71 Tow/Haul Mode switch (Momentary Ground)
75 PCM IGN Supply (12+ switched)

C2 RED
9 Fuel Pump Relay Control
10 Tach output signal [connects to white wire behind cluster?]
16 4WD Low signal (only used if VSS on Tcase Output)
33 Fan 2 Relay ground
38 Fuel gauge output (runs level gauge on 96-99 trucks)
46 CEL signal wire
50 VSS output [connect to light blue wire with black stripe and red wire with white stripe in DRAC box?]

So... I beleive the ones in bold are the only ones I'm not fairly confident of what to do with. I'm fairly confident that the rest will be fairly easy to figure out.


NOTE: This pinout ignores EVAP, rear O2s, AC, and probably a few others some people may care about but I tried to make this not just dedicated to my swap, as I've found the info out there for where to actually hook this stuff up seriously lacking (compared to all of the other topics).

Also, I see nothing in the factory harness info I found for oil pressure... this surprised me. Wouldn't it be wise of a MFR to have a low oil pressure safety built into the ECU?

the PCM does not care for oil pressure, you can use the stock plug on the actual truck harness and use it on the Oil pressure sensor, as for the TCC lockup brake switch deal, im still trying to figure that one out.
It would help you alot if you found a pinout for your year model truck

[greenvortec]

the PCM does not care for oil pressure, you can use the stock plug on the actual truck harness and use it on the Oil pressure sensor, as for the TCC lockup brake switch deal, im still trying to figure that one out.
It would help you alot if you found a pinout for your year model truck

Hey man, Redheartbeat told me what to do and it works. go under your dash and find the brake switch, there should be a purple wire that comes out of it along with a few others, i tested mine with a volt meter first, it needs 12v with the pedal untouched and 0v with it pressed down!

[Wagonbacker9]

5th post updated with what I believe to be complete info based on forum research.

[Dustytrix]

For the tach on a 92 silverado I connected to the white wire that was on the coil, using the red wire that was on the coil for ignition switched power. But even using the white tach wire that was on the coil you need a 680 ohm resistor. It will read only half rpms that you are running, I don't know how to get that straight but its better than nothing. you are right also with the existing fuel pump relay tie into the green/wht wire. Hope this helps.

[Wagonbacker9]

For the tach on a 92 silverado I connected to the white wire that was on the coil, using the red wire that was on the coil for ignition switched power. But even using the white tach wire that was on the coil you need a 680 ohm resistor. It will read only half rpms that you are running, I don't know how to get that straight but its better than nothing. you are right also with the existing fuel pump relay tie into the green/wht wire. Hope this helps.

Appreciate the input.