LS wiring question
 

So where is everyone mounting their PCM unit and also the fuse box for the LS engine wire harness. Just got my engine kit and box and plugs are too big for me to get them thru the firewall since I have it finished and painted. Ordered a complete new engine wire harness for my 5.3 LS. I will have to put in engine bay somewhere and wanted to see what everyone has done.

Re: LS wiring question
 

I have an LS 6.0 motor in my 1955 truck. I hung the PCM, fuse block and relays on the drivers inner fender.

Re: LS wiring question
 

are you trying to feed the plugs thru the firewall from inside the truck to the engine?..ecms just don't look right under the hood of these old trucks...my next ones going under the seat..my last one was behind the dash..but on my harness it feeds thru the firewall from inside the cab to the engjne...the harness should have a firewall grommet that dictates what size hole you'll need...the grommet will hide the hole made with a hole saw

Re: LS wiring question
 

If you do decide mount the pcm on the inside of the firewall, cover the area where the hole needs to be with tape then drill the hole. Use a good hole saw and you should not have any paint damage that is not cover by the grommet.

Re: LS wiring question
 

This is what we did on the LS and PCM

Re: LS wiring question
 

I have an LQ4 in my ‘55.2 now. ECM s mounted under the seat. Fuse panel behind the gauge cluster between the dash reinforcements. I didn’t want the wiring to show so it runs on the floor under the Dynamat and up the toe board to under dash.

Re: LS wiring question
 

Nice! Time to go thru your build thread:metal:

Re: LS wiring question
 

I extended the harness and mounted the PCM under the seat. I used an S10 PCM bracket to mount it https://www.summitracing.com/parts/n...SABEgKVm_D_BwE I ran the wire bundle down the transmission and then drilled a hole under the seat. My fuses are mounted high on the driver's side kick panel along with the OBDII and check engine light for easy access.

I don't have any pic, my truck is torn apart for paint right now.

Re: LS wiring question
 

I forgot to mention that I didn’t use the stock GM harness.

used the Holley Dominator ECU which comes with longer wires so I didn’t have to extend the stock harness.

https://www.amazon.com/gp/aw/d/B0049...UHL&ref=plSrch

Re: LS wiring question
 

I48, post up some pics of under hood and cab so we can see what you have for room.
could you install under floor like another sealed battery box with a lid accessed from inside the truck?
under seat on a tray that slides out for access?
behind seat where fuel tank used to be? (assuming it's under the truck)
behind dash glove box, accessed from inside or through access hatch on firewall?

it depends on what you have changed etc. original park brake, steering column, dash, fuel tank etc

Re: LS wiring question
 

I put mine under the dash but would never do that again. Now that everything is put together I dread ever having to get to it. Next time either under the seat or (prefer) behind the seat

Re: LS wiring question
 

Thanks everyone. Lots of things to think about. Can look at doing the extending but may go with this setup. So many decisions. :lol:

Re: LS wiring question
 

Dwcsr, did you make those shields and also did you end up making a cover or will you leave it like that? I have same vintage air set up so kind of like this idea.

Re: LS wiring question
 

Very clean looking. I am just worried about cutting and extending wires on a $600 engine harness. I am definitely not an electrician. :dohh:

Re: LS wiring question
 

I mounted all my electronics behind the seat. Easy access but it is a bit of work up front.
Rob

Re: LS wiring question
 

I put both under the seat. It wasn't hard to extend, but time consuming. Just do one wire at a time and solder/ heat shrink. May consider a plug so you don't have to remove the harness from engine if you ever have to pull it.

Re: LS wiring question
 

yikes Dan, a $2000 computer? I've got a $350 Mega-Squirt.

Re: LS wiring question
 

I am using a truck harness that has been re-pinned but not lengthened. What worked for me was mounting it on the passenger inner fender, close to the battery (in the stock location).

If I had to do it over again, I would spend the extra time to lengthen the harness and hide it under the dash. Eventually, I will end up doing this.

I am with everyone else, an ECM looks out of place under the hood.