Where to put the PCM??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Pontitruck · 01-26-2019, 08:03 PM

Hi guys,

Where is everybody putting their PCMs on the 64-66 trucks? I have a 65 GMC 5.3 swap going on and I'd like to hide all the wiring but am also adding Vintage Air so space is limited. Please post up your pics and suggestions, thanks!

Joe

**nsb29** · 01-26-2019, 09:37 PM

Put mine under the seat

Pontitruck · 01-26-2019, 10:05 PM

Quote:

Originally Posted by nsb29

Put mine under the seat

And the fuses and relays? Do you have carpet over all the wiring? Any pics?
Thanks

**mongocanfly** · 01-27-2019, 12:17 AM

I'd go under the seat if possible with everything..

BR3W CITY · 01-27-2019, 02:38 AM

Orignally had mine mounted on the inner fender well with fuses etc, but when I rebuilt my truck and ditched the inners, we relocated all the ecm stuff to the passenger upper footwell area. May not be an option since you'll have a/c ducting.

Pontitruck · 01-27-2019, 08:23 AM

For those that are locating them under the seat on a 64-66 what harness is long enough, aftermarket? Rewired OEM? I would appreciate any pics you have.
Thanks

**nsb29** · 01-27-2019, 09:30 AM

I don’t have pictures but wiring onder carpet made my own harness

**mongocanfly** · 01-27-2019, 12:23 PM

I've used PSI on all my swaps...their harnesses have 4-5 ft of wire from the back of the head...I contacted several of the "store bought" harness makers and none would make a longer harness.....with the LS swap being so popular ,you would think someone would offer a long harness...if you build your own you can make it however you want....I know PSI is coming out with a DIY kit...
Of all the engines I've bought I have yet to get the factory harness that wasn't damaged in some way....

**nsb29** · 01-27-2019, 02:06 PM

Quote:

Originally Posted by mongocanfly

I've used PSI on all my swaps...their harnesses have 4-5 ft of wire from the back of the head...I contacted several of the "store bought" harness makers and none would make a longer harness.....with the LS swap being so popular ,you would think someone would offer a long harness...if you build your own you can make it however you want....I know PSI is coming out with a DIY kit...
Of all the engines I've bought I have yet to get the factory harness that wasn't damaged in some way....

5ft mite be long enough

BR3W CITY · 01-28-2019, 12:28 PM

Quote:

Originally Posted by mongocanfly

I've used PSI on all my swaps...their harnesses have 4-5 ft of wire from the back of the head...I contacted several of the "store bought" harness makers and none would make a longer harness.....with the LS swap being so popular ,you would think someone would offer a long harness...if you build your own you can make it however you want....I know PSI is coming out with a DIY kit...
Of all the engines I've bought I have yet to get the factory harness that wasn't damaged in some way....

Ask for the Van harness instead of the truck harness. It adds length to the main trunk of the harness.

Pontitruck · 01-29-2019, 10:00 PM

Quote:

Originally Posted by BR3W CITY

Ask for the Van harness instead of the truck harness. It adds length to the main trunk of the harness.

Who sells a converted van harness??

**1971Stepside** · 01-28-2019, 01:03 PM

Call BP Automotive. Their harness is made to put the PCM under the seat. The one for my 71 is more than long enough. The harness is a work of art as well. Labled and easy to install.

Pontitruck · 01-29-2019, 10:06 PM

Quote:

Originally Posted by 1971Stepside

Call BP Automotive. Their harness is made to put the PCM under the seat. The one for my 71 is more than long enough. The harness is a work of art as well. Labled and easy to install.

Called them, they provide 5ft of wire from the back of the passenger side of the intake. My PSI harness for the manual trans I'm taking out is only 4ft so the extra foot may allow it to be mounted under the seat.
They will also extend it 3' for $100

**mongocanfly** · 01-28-2019, 03:52 PM

Thanks 71 step...Wish I knew that before....BP is one I didnt contact...
and thanks brew...I'll have to remember that next time about a van harness

scoot_mcgrute · 01-29-2019, 12:17 PM

I've got computer below the radiator and the relays are on the inner fender tucked up against the core support. Makes for a nice and seamless install that doesn't draw a lot of attention to the things that aren't supposed to be there.

Pontitruck · 01-29-2019, 10:03 PM

Quote:

Originally Posted by scoot_mcgrute

I've got computer below the radiator and the relays are on the inner fender tucked up against the core support. Makes for a nice and seamless install that doesn't draw a lot of attention to the things that aren't supposed to be there.

Won't there be a lot of water hitting that if driving in a rain storm? I definitely like the clean look though.

scoot_mcgrute · 01-30-2019, 12:28 PM

Quote:

Originally Posted by Pontitruck

Won't there be a lot of water hitting that if driving in a rain storm? I definitely like the clean look though.

Potentially, yes but remember that these computers use sealed connectors and they also have a water intrusion rating. I don't drive in the rain on purpose but when I have been caught in it, it hasn't been an issue. They get doused with water all the time in 4x4s so it really isn't any different.

BR3W CITY · 01-30-2019, 12:45 PM

Quote:

Originally Posted by Pontitruck

Who sells a converted van harness??

If your providing a donor harness for rework, anyone will do it the same as a regular truck harness. If your having a harness made, just ask, some will make you the harness instead of just selling a premade truck swap harness for everything.

Quote:

Originally Posted by scoot_mcgrute

Potentially, yes but remember that these computers use sealed connectors and they also have a water intrusion rating. I don't drive in the rain on purpose but when I have been caught in it, it hasn't been an issue. They get doused with water all the time in 4x4s so it really isn't any different.

Back when my ECM and harness were on the inner fender, I drove without a hood to the CarCraft Nationals and got caught in a freaking torrent. The intake tube was less happy, the harness and computer didn't care.

El_C10 · 01-29-2019, 06:38 PM

Quote:

Originally Posted by Pontitruck

Hi guys,

Where is everybody putting their PCMs on the 64-66 trucks? I have a 65 GMC 5.3 swap going on and I'd like to hide all the wiring but am also adding Vintage Air so space is limited. Please post up your pics and suggestions, thanks!

Joe

Mounted mine right behind the cluster, right above the parking brake assembly. Fits snug but it fits.

Pontitruck · 01-29-2019, 10:01 PM

Quote:

Originally Posted by El_C10

Mounted mine right behind the cluster, right above the parking brake assembly. Fits snug but it fits.

Must see pics!

**1971Stepside** · 01-30-2019, 10:46 AM

Here is what mine looks like in a 71.

beaterku · 01-30-2019, 11:17 AM

I am mounting mine under the seat. I am using a PSI harness. I can attest that I wish the PSI was about a foot longer. It will work, but the extra wire would have been nice.

My mount is from Motobilt https://www.motobilt.com/product/ls_engine_ecm_mount

Putzer · 02-01-2019, 09:15 PM

Quote:

Originally Posted by 1971Stepside

Here is what mine looks like in a 71.

can you give me a measurement to compare my harness to so i can see if my harness will be long enough? Mine is from speartech but theres just not really a good way to tell without drilling the hole first i think. Love the utube vids btw.

jrusher · 02-03-2019, 12:18 AM

Bolted it to the rad support on the grille side, tucked away nice out of sight. My harness was a 2008 van harness so was extra long but was easy to tuck all the slack wire in under grille/rad support

bigmoe · 02-05-2019, 06:46 PM

Is it an option to lengthen a stock harness? I assume it would involve splicing to make the PCM end of the harness longer. I like the idea of mounting the PCM somewhere out of the way like under the console/seat or behind the glove box but I assume the stock harness is too short. I've seen them mounted to the inner fender but it's not a very clean look.

01-26-2019, 08:03 PM	#1
Pontitruck Registered User Join Date: Sep 2018 Location: South of the Indy 500 Posts: 116	Where to put the PCM??? Hi guys, Where is everybody putting their PCMs on the 64-66 trucks? I have a 65 GMC 5.3 swap going on and I'd like to hide all the wiring but am also adding Vintage Air so space is limited. Please post up your pics and suggestions, thanks! Joe

01-26-2019, 09:37 PM	#2
nsb29 Senior Member Join Date: Feb 2014 Location: new smyrna beach fl / 29 palms cal Posts: 1,727	Re: Where to put the PCM??? Put mine under the seat

01-27-2019, 12:17 AM	#4
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: Where to put the PCM??? I'd go under the seat if possible with everything.. __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

01-27-2019, 02:38 AM	#5
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Where to put the PCM??? Orignally had mine mounted on the inner fender well with fuses etc, but when I rebuilt my truck and ditched the inners, we relocated all the ecm stuff to the passenger upper footwell area. May not be an option since you'll have a/c ducting. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

01-27-2019, 08:23 AM	#6
Pontitruck Registered User Join Date: Sep 2018 Location: South of the Indy 500 Posts: 116	Re: Where to put the PCM??? For those that are locating them under the seat on a 64-66 what harness is long enough, aftermarket? Rewired OEM? I would appreciate any pics you have. Thanks

01-27-2019, 09:30 AM	#7
nsb29 Senior Member Join Date: Feb 2014 Location: new smyrna beach fl / 29 palms cal Posts: 1,727	Re: Where to put the PCM??? I don’t have pictures but wiring onder carpet made my own harness

01-27-2019, 12:23 PM	#8
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: Where to put the PCM??? I've used PSI on all my swaps...their harnesses have 4-5 ft of wire from the back of the head...I contacted several of the "store bought" harness makers and none would make a longer harness.....with the LS swap being so popular ,you would think someone would offer a long harness...if you build your own you can make it however you want....I know PSI is coming out with a DIY kit... Of all the engines I've bought I have yet to get the factory harness that wasn't damaged in some way.... __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver Last edited by mongocanfly; 01-27-2019 at 12:30 PM.

01-28-2019, 01:03 PM	#12
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	Re: Where to put the PCM??? Call BP Automotive. Their harness is made to put the PCM under the seat. The one for my 71 is more than long enough. The harness is a work of art as well. Labled and easy to install. __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

01-28-2019, 03:52 PM	#14
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: Where to put the PCM??? Thanks 71 step...Wish I knew that before....BP is one I didnt contact... and thanks brew...I'll have to remember that next time about a van harness __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

01-29-2019, 12:17 PM	#15
scoot_mcgrute Registered User Join Date: Apr 2004 Location: Tigard, Or Posts: 503	Re: Where to put the PCM??? I've got computer below the radiator and the relays are on the inner fender tucked up against the core support. Makes for a nice and seamless install that doesn't draw a lot of attention to the things that aren't supposed to be there. __________________ 1966 Army Truck http://67-72chevytrucks.com/vboard/s...d.php?t=691778

01-30-2019, 10:46 AM	#21
1971Stepside Almost Satisfied Join Date: Mar 2002 Location: Springfield, MO Posts: 2,932	Re: Where to put the PCM??? Here is what mine looks like in a 71. Attached Images __________________ 1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3200 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Finally back on the road in 2021. "I can't complain, but sometimes I still do. Life's been good to me so far."

01-30-2019, 11:17 AM	#22
beaterku Registered User Join Date: Mar 2013 Location: Lenexa, KS Posts: 547	Re: Where to put the PCM??? I am mounting mine under the seat. I am using a PSI harness. I can attest that I wish the PSI was about a foot longer. It will work, but the extra wire would have been nice. My mount is from Motobilt https://www.motobilt.com/product/ls_engine_ecm_mount Attached Images __________________ www.rustywrenches.com My 72 SWB build My YouTube channel

02-03-2019, 12:18 AM	#24
jrusher Registered User Join Date: Mar 2017 Location: Edmonton Posts: 390	Re: Where to put the PCM??? Bolted it to the rad support on the grille side, tucked away nice out of sight. My harness was a 2008 van harness so was extra long but was easy to tuck all the slack wire in under grille/rad support Attached Images

02-05-2019, 06:46 PM	#25
bigmoe Registered User Join Date: Oct 2014 Location: Brandon, Manitoba, Canada Posts: 995	Lengthen a stock harness? Is it an option to lengthen a stock harness? I assume it would involve splicing to make the PCM end of the harness longer. I like the idea of mounting the PCM somewhere out of the way like under the console/seat or behind the glove box but I assume the stock harness is too short. I've seen them mounted to the inner fender but it's not a very clean look.



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