Harness Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**MidLifer** · 09-04-2018, 09:22 PM

I've been back at my delayed 50 3100 build this year. Got the finishing body work done by a local shop, now making final preparations before it goes out for paint. The body man put a smooth firewall on over the existing firewall, which looks awesome, but I would like to figure out what holes need to go into it before it goes to the paint shop.

The truck will have a 235/T5 and Vintage Air. I know I need to open up the old fan hole for the VA setup. What I'm trying to figure out is the wiring harness. I bought an American Autowire harness from MCB (board vendor) and probably will mount it behind the dash. I've been scanning build threads on this forum but haven't yet found the photo I'm looking for, which is someone who used a harness like that and how many/how big holes were needed to get the wires through the firewall.

Kind of a strange request I know, but what else is this forum for?

dsraven · 09-05-2018, 02:40 AM

you could always run the wiring through the floor area to be out of sight. it would need to be slightly longer though.
you could also do a bulkhead connector that attaches to the firewall and seals the wiring connection there so moisture doesn't get through from the engine side. like a more modern vehicle would have
you could come in through the side kick panel behind the fender to hide the wiring thru hole.
just a few thoughts.

MiraclePieCo · 09-05-2018, 03:20 AM

Hot Rod magazine did an entire article about wiring an AD truck. Here's a link to the photos; maybe give you some ideas:

https://www.hotrod.com/articles/0806...31_z-wire_done

69l46vert · 09-05-2018, 08:22 AM

Check your A/A directions. Most of those type harnesses use a 1 1/4 hole. And usually they come with a grommet for a 1 1/4.

**MidLifer** · 09-05-2018, 11:36 AM

Thanks all.

I looked at the directions before searching/posting and did not see anything about firewall holes, nor did I see a grommet in the package, but I'll check again.

The Hot Rod article gives a lot of good ideas too. I may look into routing the wire under the floor to make the engine bay look cleaner and show off my smooth firewall.

Pics of the project to follow.

09-04-2018, 09:22 PM	#1
MidLifer Senior Member Join Date: Apr 2011 Location: South NJ Posts: 1,257	Harness Help I've been back at my delayed 50 3100 build this year. Got the finishing body work done by a local shop, now making final preparations before it goes out for paint. The body man put a smooth firewall on over the existing firewall, which looks awesome, but I would like to figure out what holes need to go into it before it goes to the paint shop. The truck will have a 235/T5 and Vintage Air. I know I need to open up the old fan hole for the VA setup. What I'm trying to figure out is the wiring harness. I bought an American Autowire harness from MCB (board vendor) and probably will mount it behind the dash. I've been scanning build threads on this forum but haven't yet found the photo I'm looking for, which is someone who used a harness like that and how many/how big holes were needed to get the wires through the firewall. Kind of a strange request I know, but what else is this forum for?

09-05-2018, 02:40 AM	#2
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 7,823	Re: Harness Help you could always run the wiring through the floor area to be out of sight. it would need to be slightly longer though. you could also do a bulkhead connector that attaches to the firewall and seals the wiring connection there so moisture doesn't get through from the engine side. like a more modern vehicle would have you could come in through the side kick panel behind the fender to hide the wiring thru hole. just a few thoughts.

09-05-2018, 03:20 AM	#3
MiraclePieCo Registered User Join Date: Sep 2014 Location: USA Posts: 2,249	Re: Harness Help Hot Rod magazine did an entire article about wiring an AD truck. Here's a link to the photos; maybe give you some ideas: https://www.hotrod.com/articles/0806...31_z-wire_done __________________ 1951 Chevy Panel Truck

09-05-2018, 08:22 AM	#4
69l46vert Registered User Join Date: May 2007 Location: Buxton Maine Posts: 137	Re: Harness Help Check your A/A directions. Most of those type harnesses use a 1 1/4 hole. And usually they come with a grommet for a 1 1/4. __________________ 1954 GMC 101-24 Converting to 4WD Stock 54 GMC 150 frame Dana 44 Front Dana 60 Rear SBC350/SM465/NP205

09-05-2018, 11:36 AM	#5
MidLifer Senior Member Join Date: Apr 2011 Location: South NJ Posts: 1,257	Re: Harness Help Thanks all. I looked at the directions before searching/posting and did not see anything about firewall holes, nor did I see a grommet in the package, but I'll check again. The Hot Rod article gives a lot of good ideas too. I may look into routing the wire under the floor to make the engine bay look cleaner and show off my smooth firewall. Pics of the project to follow.



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