Seeker1056

anyone out there know what pcm pin number the tow haul button is activated by?

tfi racing

iTrader: (2)

Which PCM? Pin 71 blue on a 411 or LS1B PCM,you will also need to program for it.

Seeker1056

its a 2003 van pcm and already tow haul, and my other one is a 2004 truck pcm
blue and green
just need to know which wire to operate

tfi racing

iTrader: (2)

Blue 71 should do it then.

Seeker1056

is it wired to an intermitant switch to ground or intermitant switched 12V
thanks

gofastwclass

iTrader: (2)

It's a momentary ground, but there is no way to know that it's enabled without a BCM.

aknovaman

iTrader: (7)

Not all P59 PCM operating systems allow Tow Haul on pin 71. Only the early OS supported it. This horse has been beaten numerous times over the years.

Seeker1056

I am looking into a latched relay to work the light - everything I read says it will work without the bcm by going that way
time will tell

Brandenhs

iTrader: (2)

I used a PAC TR-7 to activate the pcm and the led in the switch. I modified the tow/haul button to use all 4 pins and it lights up when pushed.

ls1nova71

iTrader: (4)

So does this come on when it's pushed and go off when it's pushed again? I have the tow/haul hooked up on my '71 and looked into the latching relay thing, but couldn't get it to turn off when the button was pushed again.

Brandenhs

iTrader: (2)

Yes you can use the button to turn it on and off or it'll shut off when you turn off the ignition.

ls1nova71

iTrader: (4)

Interesting. Do you have a schematic on how you wired it up? Right now I just have the single momentary to ground wire coming from the BCM, where would this hook up?

gofastwclass

iTrader: (2)

The root problem with a swap - in my humble opinion - is there is no way to know Tow Haul is truly active without the BCM or reading the data bus directly.

Building a latching relay setup that counts the button pushes as mentioned above is cool, but if it gets out of synch for some reason it isn't accurate. Still cool though.

76larkman

why couldn't tell by rpm change while driving? seems like you would know by tach.

Brandenhs

iTrader: (2)

Idont want to hijack this thread so I made a tut on how I did mine. this also addresses the problem of it not latching. I have used it over 100 times this summer trying new shift points and it worked every time. https://ls1tech.com/forums/conversio...l#post19126277

zipster

iTrader: (5)

I bought this,
http://www.ebay.com/itm/Bistable-Flip-Flop-Latch-Switch-Circuit-Module-Button-Trigger-Power-off-Memory-/201412532274?hash=item2ee51f5832
It uses a momentary negative to activate a relay, that momentary negative will also trigger the tow/haul mode on pin 71. the relay will activate a led. When power is removed, the ecm will go into non tow/haul mode and the relay will turn off.

I have not connected it to the car yet. But I fell it will work just fine. Plus it was $6

Seeker1056

ok - so I am working on my third truck harness
i personally pulled the pcms and harness from the trucks and know they had tow haul because i purposely checked
having said that - this is the third harness where Blue pin 71 has never been used meaning it never had a pin in it before- yet I am told here that Blue pin 71 is the right pin to use

how can that be when one of the original, already used pins has to be the tow haul pin

what am I missing? what pin did the factory use for tow haul and why are we not re-using it? or is this another one of those BCM deals which will prevent reusing tow haul without wiring in a BCM

these are 2003 and 2004 pcms and harnesses for vans/trucks blue green pcms
from what I have been googling - B-71 only works on red blue pcms

next question - we will be using 2002 programing as EFI Live COS files require that operating system to work properly
By switching to the 2002 programing - will that allow the use of pin 71?

thanks

ls1nova71

iTrader: (4)

The factory controlled it by the BCM. You have to add the wire to get around that. Some tuning may also be needed.

Project GatTagO

iTrader: (7)

I am just a bystander in this discussion, but what does the tow/haul button do?

Andrew

ls1nova71

iTrader: (4)

Not a lot for the trouble. It firms the shifts, holds gears a little longer and keeps it from going into overdrive until you're at a higher speed. Pretty sure it can all be changed in the tune to be more aggressive, but this is what they do stock.