Help

[nsb29]

It’s been a while since I built my engine harness. Now I wiring the rest of the truck and I have two wires marked brake switch one from the ECM and one from trans do both go to brake switch?

[prodjay10]

Isn’t one power constant and the other goes to ecm? I believe both go to the brake switch.

[ls1nova71]

What year is the engine/harness?

[nsb29]

Originally Posted by ls1nova71

What year is the engine/harness?

2009 6.0 and 6l80E out of a Pontiac G8

[ls1nova71]

Well, I feel like I shouldn't help you since you must have killed a G8 to get that engine...... Lol!

But anyway, they both tie together and go to the ECM X1 pin 9. That being said, I have never messed with that harness so not sure how you would go about hooking it to the brake switch since the G8 uses a brake pedal position sensor that is wired to the BCM then the info is sent to the ECM via the CAN Bus. I'm sure there's a work around, and maybe you already know what it is?

[nsb29]

Originally Posted by ls1nova71

Well, I feel like I shouldn't help you since you must have killed a G8 to get that engine...... Lol!

But anyway, they both tie together and go to the ECM X1 pin 9. That being said, I have never messed with that harness so not sure how you would go about hooking it to the brake switch since the G8 uses a brake pedal position sensor that is wired to the BCM then the info is sent to the ECM via the CAN Bus. I'm sure there's a work around, and maybe you already know what it is?

Well the G8 was dead when I got if that helps Ha Ha. so far almost everything I did to the harness was the same as the Camaro other than a couple of wires to the gas pedal. Have no knowledge About the brake pedal positioning sensor if you’re right I guess I’m going to have to learn just assumed it was the same as the Camaro

[ls1nova71]

The Camaro was based off the G8 so probably why it's similar. I just looked up the wiring diagram and that's what it showed. I can look up the Camaro later and see if it's the same but wont be home until the morning.

BTW, this is the only vehicle I have ever owned that came factory with an LS. I'm kind of partial to them!

[nsb29]

Thanks any help would be greatly appreciated. Nice looking car do you still have it

[ls1nova71]

I looked up the Camaro schematic and it's the same as the G8. I'm pretty sure it will wire up like any other genIV engine where you just need to hook it to the normally open side of the brake switch so that it gets 12v when the brake pedal is applied, that is how the trucks are wired.

Oh, and yes, I still have my G8.

[nsb29]

Thanks I appreciate the help so if my understanding is right the white wire with the blue tracer comes from the transmission two pin number nine on the ECM and from there to my brake light switch n/o I was thinking it went to the n/c but maybe that’s my Cruise control thanks again Doug

[nsb29]

I went back to my notes and LT1swap.com shows that the wire goes to n/c not to n/o side of the brake switch, I think ls1nova miss tipped when he said n/o side

[ls1nova71]

I'm pretty sure on all GenIV engines the brake switch wire needs 12v when the brakes are applied. GenIII engines need a 4 prong brake switch where one set of contacts will be hooked up to give 12v when the brakes are not applied,. I looked at LT1swap and cant find anything to the contrary?

[kipps]

Originally Posted by ls1nova71

...But anyway, they both tie together and go to the ECM X1 pin 9. That being said, I have never messed with that harness so not sure how you would go about hooking it to the brake switch since the G8 uses a brake pedal position sensor that is wired to the BCM then the info is sent to the ECM via the CAN Bus....

Assuming the G8 is similar to the gen V camaro--

The BCM has a dedicated three-pin brake sensor. Based on info from that sensor, the BCM creates the necessary 12v brake signals for everything else. This includes the brake lights and x1-9 on the ECM. There is literally a wire(circuit #6311) from the BCM to x1-9 on the ECM that's energized to 12v when the BCM decides the brakes are applied.

There's also some evidence of a brake signal being passed between the BCM and the ECM on the CAN bus. The cruise control "description-of-operation" makes mention of this dual signal path. If you don't intend to use a BCM and cruise, it's possible you won't need that CAN bus brake signal, and instead can keep only the x1-9 12v signal for torque converter lockup, etc. I don't know on that one.

I'm using a camaro tune on a vortec engine, to give me a clutch pedal sensor and a manual transmission VSS. I'm also intending to use a Camaro BCM for cruise control. Hence my research into the muddy waters of brake circuits.

Note that this is quite different from the truck engines. Those don't use the three wire variable brake pedal sensor. Instead, they have a more typical brake switch. This brake switch feeds the BCM for light control, but it also directly feeds the ECM via x1-9.

[nsb29]

Well being new at this I have misunderstood what I read, I had actually gotten a brake light switch that has four terminals thinking it was supposed to be normally closed not realizing there was a difference between the trucks and the Camaro. Am I correct in assuming if I wanted to add cruise control I would need a BCM. Another question I have is I don’t understand what a can bus is or what it does. I appreciate y’all helping me through this sometimes I’m a little slow lol

[clay68c10]

The CAN bus is kind of like internet for the car. It sends coded and addressed signals to all the modules connected to the bus instead of just power and ground voltages to one single component.
For instance, you want to roll up your R rear window in your 2019 Oldsmobuick. You press the switch on the drivers door. The switch pack is actually a small computer. It sees the switch signal, makes a coded message that says “roll up R rear window.” The switch module puts that message out on the CAN bus, addressed to the R rear door module. The R rear door module sees the message addressed for it, receives the message, and then provides appropriate power and ground to the window motor. All the other modules on the bus see that the message isn’t addressed to them and they ignore it.
Haha simple, right?
The actual benefits are that it is less complex from a wiring standpoint since you don’t have to directly wire things across the car. Just wire outputs like motors, and inputs like switches to the module that is physically closest.
It also allows sharing of info between systems. Previously you had separate coolant temp sensors for the temp gauge, the engine computer, and the climate control. Now there’s just one and the engine module sends that temp info out to whichever modules need it.
All that is way slick and works great when the whole car is set up for it. It’s not so easy when we start swapping these engines into old vehicles and need something as simple as a brake switch input or AC compressor request.

[kipps]

The ECM of either the truck or the Camaro wants to see a normally open 12v signal to x1-9. When the brake pedal is depressed, it shunts 12v to that pin. There's a good chance that the x1-9 pin wants to see a ground connection when it's not energized. This could be a relay or a brake light filament. If you're just using LED bulbs, it could give you issues. I've gotten conflicting info on this, though.

I've gathered that the older gen III's needed a normally closed brake signal going to the ECM, so the gen IV's are different in that aspect.

The truck BCM needs a normally open and a normally closed brake signal for cruise control. The camaro BCM needs a three-wire voltage divider sensor for the brake signal. There's some chance that can be swapped out for a simpler sensor(simpler to mount), but I need to experiment more with that.

Yes, the BCM is required for cruise control and smart charging, if you're only using Chevrolet components. A more common cruise control option, is to buy a kit from Dakota Digital or The Cruise Control Store, which is pretty much plug-and-play. It comes with a price, though.

The 2010 stuff I'm playing with has two CAN buses. High speed, also called GMLAN, and low speed. The low speed bus is a single wire connecting the anti-theft module, the instrument panel cluster, the door modules?, the radio, and others all back to the Body Control Module. I'm not using this system at all, so I'm not well versed in it's operation. The High speed GMLAN bus is the one I'm focusing on. I assume your car is similar. This is a pair of twisted wires, usually labeled 2500 and 2501 on the diagrams, that connects the ECM, TCM, BCM, DLC(obd2), FSCM(fuel system control module), and(I think) a brake control module. I'm only using three components on this bus. The ECM, BCM, and DLC. If you're using the factory automatic, you'll also need to include the TCM in the mix.

[nsb29]

Well somethings are clear and questions answered but with that said it also create more questions, as far as the Can bus is concerned I somewhat understand I am in the garage door business and the garage door opener’s wall control panel has a printed circuit board which sends multi functions to the opener in a single pair of wires. I also now understand that it is not the Camaro or the truck but the New generation versus older generation. The 2009 6L80 E transmission has the TCM built in. As far as the BCM goes if I need one I’ll get one as I would like to have cruise, I know my brother bought an aftermarket cruise control For his 66 but he is also running a different motor and transmission and I don’t know what generation, he said it was plug-and-play. My next question is what is the DLC and what does it do I really appreciate you and ls1 nova taking the time to explain this stuff to me I hope I am capable of understanding it lol

[kipps]

The DLC is simply GM's name for the obd2 port at the driver's left knee. On the Gen IV's, the DLC has three data wires pinned to it in addition to power and grounds. Two of those wires are high-speed bus wires, and one is low-speed. If you're not using the BCM, you can skip the low-speed wire.

Think of the CAN bus(both high speed and low speed) as the equivalent of a USB cord. A USB cord or Ethernet cord allows multiple computers to talk together and exchange data. They can move a lot of info over four wires. The CAN buses are similar. Using only one or two wires, they allow computer modules to talk together.

Another analog data transfer which might seem similar but it's not, is involving "resistor ladder" switches. Many of the functions on the dash are directly wired to the body control module. If every switch had it's own dedicated wires going to the BCM, there'd be way too many wires. Instead, a group of switches will all have a common hot and a common signal wire. Depending on which switch you press, it connects a different value of resistor between the hot and signal wires. This way, five switches only have two wires connecting them to the BCM. The cruise switches(and many others) are this way. I'm pasting a 2010 Camaro cruise control diagram, to show how this kind of switch works. Note that there is no computer stuff involved in that switch. It's purely analog.

The use of a BCM with a GEN IV swap is not well documented. I've never found any tutorials or how-to's for doing such. Enough folks have done it that I'm sure it can be done, but it's not as easy as many other aspects of these swaps.

I strongly recommend you buy a subscription to alldata for your donor vehicle. If you're doing a well-documented swap, such as a stock gen III, it might not be needed, but for anything involving transmission swaps, gen IV or V, DIY harness mods, donor vehicle fuse boxes, Body control modules, etc, you've got to have access to those factory diagrams.

[nsb29]

My sun has access to all data the problem there is knowing what I need or what I’m looking at. I have a lot of stuff printed out on this swap and so far it’s been very helpful. I grew up around points and carbs and this is my first LS swop, so this has been a learning curve for me but I’m learning thanks

[nsb29]

I have another question, What c/c switches do I use to activate the cruise on off set, resume?

[kipps]

What truck are you working with? I found this diagram for the '84+ four-wire cruise switch. I'm soldering up a small padboard with a couple of resistors to adapt the '84+ switch to the BCM. Haven't done it yet, though.

[nsb29]

My truck is the 65 with the stock steering column

[kipps]

Originally Posted by nsb29

My truck is the 65 with the stock steering column

I can't really help you with that one. You'll need to find a cruise stalk that will adapt to your column, or go with rocker switches mounted somewhere in the dash. Based on the diagram in post #18, you'll need a latching on/off switch for cruise on/off. You'll also need momentary switches for resume/accelerate, set/decelerate, and cancel.

I'm intending to skip the cancel switch, since the '84+ stalk doesn't have it. I'll just need to tap the brake pedal to cancel the cruise.

I don't intend to, but the on/off switch could be skipped as well, and just leave the cruise wired in the "on" position. There's arguably some safety concerns with this, though.

[nsb29]

Another thing I don’t understand is I have read that led taillights don’t draw enough power, so does this mean that the ECM can detect the draw of the taillights or does it detect the ground. And does this change between the generation’s as n/c verses n/o. I don’t plan on LED just trying to get my head around it

[ls1nova71]

What you need is a lever from a 1981 chevy or GMC van, or a 1981-83 truck. The 81-82's are 3 wire but can be converted to 4 wire switches.