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PostPosted: Mon Jul 05, 2021 6:43 am 
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EFI Slant 6

Joined: Mon May 26, 2014 4:02 pm
Posts: 339
Location: Vermont
Car Model: Slant Six powered M37
I am creating a new electrical system for my M37 w/slant 6 installation.

The present moment question that I am unsure about goes something like this: I am using a fuse block out of a 77 D200. It has more fuse circuits than I will need, and it was free with the donor vehicle. That being the back ground, where does the fuse block go? That is to ask, does the fuse block feed the ignition switch, lights, and wipers? That seems like the way it should be, but I would like confirmation before proceeding.

Also, at this moment I am planning on using the starter positive stud, as a power point. The battery is under the passenger seat, and thinking the charging cable and vehicle's electrical needs could all meet at the starter positive, keeping the #s of wires going under the cab to a minimum. Any thoughts on such a plan are welcome. This is the first "from scratch" electrical wiring I have ever attempted.


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PostPosted: Mon Jul 05, 2021 8:27 am 
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Turbo Slant 6
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Joined: Sat Sep 13, 2014 8:25 am
Posts: 713
Location: Springtucky OR
Car Model:
Wherever you connect to for power the first thing should be a fusible link. Then to the ignition switch and wires from the switch to the fuse block.

One way to approach making a harness from scratch is to start with a digital image of a wiring diagram and erase all the lines that pertain to circuits you don't want to use.

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PostPosted: Mon Jul 05, 2021 1:18 pm 
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Supercharged
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Joined: Sun Nov 03, 2002 9:20 pm
Posts: 12948
Location: Fircrest, WA
Car Model: 76 D100
Get a factory service manual for a 1977 Dodge truck. That will answer all of your questions.


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PostPosted: Tue Jul 06, 2021 6:57 am 
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EFI Slant 6

Joined: Mon May 26, 2014 4:02 pm
Posts: 339
Location: Vermont
Car Model: Slant Six powered M37
Thanks for the help guys.

Yes there will be fuseable links at the battery. That part I understand.

ProCycle wrote:
Wherever you connect to for power the first thing should be a fusible link. Then to the ignition switch and wires from the switch to the fuse block.


So all the electricity that flows when the key is in the "on" position goes through the ignition switch?

This is where I am getting confused.

Reed wrote:
Get a factory service manual for a 1977 Dodge truck. That will answer all of your questions.


I've got one, and while I can see-imagine the electric flow when looking at the diagram.... I do not understand what I am seeing well enough to comprehend how turning the ignition switch on energizes circuits such as the wipers, blower motor, and ignition, with out sending all of that electricity through the ignition switch itself.. I can imagine doing it with a relay, to limit the current the switch has to deal with, but in looking at the wiring diagram, I am getting lost.


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PostPosted: Tue Jul 06, 2021 8:27 am 
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Turbo Slant 6
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Joined: Sat Sep 13, 2014 8:25 am
Posts: 713
Location: Springtucky OR
Car Model:
Jase wrote:
...So all the electricity that flows when the key is in the "on" position goes through the ignition switch?

This is where I am getting confused...

Everything that comes on when you turn the switch does. Except those things that are powered through a relay like the headlights, horn, etc. In that case the power that will energize the relay flows through the ignition switch. I'm sure your wiring diagram shows which circuits are connected/disconnected in each key position. The ignition switch is fully capable of supporting fairly high current.

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PostPosted: Tue Jul 06, 2021 1:45 pm 
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EFI Slant 6

Joined: Mon May 26, 2014 4:02 pm
Posts: 339
Location: Vermont
Car Model: Slant Six powered M37
OK that is good to hear. I will quit worrying about it and get started.


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PostPosted: Tue Jul 06, 2021 2:51 pm 
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Turbo EFI
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Joined: Wed Oct 12, 2005 9:00 pm
Posts: 2370
Location: kankakee IL
Car Model: 80 volare, 78 fury 2 dr, 85 D150
I basically did as you are talking about, on my 85 D150. It came to me, with thee most butchered, rigged wiring harness, that I have ever seen. were talkin (not the only problem/ but the 1st thing spotted, right off the bat) In the length of a /6 valve cover, the "HOT" wire off the alt changed color and gauge 3x. Just twisted and taped and not very well at that... One such splice was directly over the fuel line from pump to carb, with strands of twisted wire close enough to the fuel line I'm surprised it didn't arc and cause a leak/fire... especially right after a bump in the road... 4 fusible links fixed in similar fashion.
I eliminated all fusible links, I wired every circuit thru an underhood fuse box off of a early 90s vehicle that I pirated from a junkyard, and everything that used to be thru a F.Link is now thru a Maxifuse. I started with a harness from another junkyard refugee, this one another mid 80s D-150. I went thru that harness and fixed thee cracked insulation,etc done to this harness by age.


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PostPosted: Wed Jul 14, 2021 7:54 pm 
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Board Sponsor
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Joined: Wed Nov 06, 2002 1:57 pm
Posts: 2096
Location: Everett, WA
Car Model:
A M37 should be able to get by with an aftermarket "hot rod" wiring kit. At the very least you will get new wires and modern fues.


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PostPosted: Sun Aug 29, 2021 11:45 pm 
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TBI Slant 6

Joined: Sun Jul 16, 2006 9:17 pm
Posts: 221
Location: NW New Jersey
Car Model:
Since you're wiring & rigging from scratch, nothing says you have to abide by some antiquated wiring diagram. If you look at modern vehicles' wiring diagrams, they isolate practically everything that draws any current with relays. That said, I recommend your ignition switch power a relay that connects battery power to practically everything that requires key-on power.

Taking that concept to the next level, I'd use relays for headlights (where the switch merely activates a relay which carries the brunt of the load), heater blower motor, wipers, and anything else requiring more than a few milliamps of current to power (again, look at 2000+ wiring schematics to see how modern vehicle's electrical systems work). Circuits that should only operate when the key is ON should get their power from the master Key-On relay. A trip to your local Pic-n-Pull may turn up a fuse block with the relays already integrated; simplifying your goals. (Chrysler has used this scheme for a couple decades. My '80s Turbo cars use it.) You might also consider using the more modern blade style fuses over the older glass types. As long as the fuse block is hidden, it won't distract from your originality look.

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