wiring harness differences
 

I have the 69 C10, originally a 6 cylinder 3 ott. The wiring on it was good.
I swapped in a 350/T350 and recently began hooking the wiring up and found some differences. I see the standard trans backup light switch was hooked into the trans. The 71 w/auto trans harness has the bkup switch/neutral safety switch located inside on the lower steering column.
One other difference I see is the wire harness across the radiator support has a couple of inline fuses in the 71 harness that my 69 harness does not have.
The schematics I have found here for 67-72 are different from what I have.
I do not intend to buy a new harness. This is just a driver.

Re: wiring harness differences
 

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Here is the ammeter fuses that I was talking about.

Attachment 1601521

Here is the horn relay and neutral start switch. You can see the green backup wires and the purple starter wires that go to it.

Attachment 1601520

and here are some wiring diagrams. The arrows are from other posts and point to various wires in the harness.

Attachment 1601522


Attachment 1601523


Attachment 1601527

Re: wiring harness differences
 

Thanks VV.
So i think all i need is to change out the engine part of the harness from the bulkhead and use my current gauge pack. If and when i should decide to change to the 7 gauge cluster i will need to change out the front harness so to include the fuses for the volt gauge. Does that sound right?

Re: wiring harness differences
 

Well it sounds like things are lining up for you. The engine harness is just about the same but when you go to change to the gauge cluster you'll have to make some changes. Mostly just swapping the wires around in the cluster plug and adding the two battery gauge wires like you said.

You'll want to do the popular mods like every body else so that will mean some added wiring or changing wires. We are on top of all of that so just ask away.

MERRY CHRISTMAS to you and yours.

Re: wiring harness differences
 

Thanks Sarge.
And Merry Christmas to you too.

Re: wiring harness differences
 

Something else Sarge.
The engine harness in those diagrams has 7 wires out of the bulkhead connector. My harness only has 5. One of those wires is a light green one. I found the reverse light switch wires inside by the fuse block so this wire is not for rev lights. In reading more threads I found this bit of info posted by Ray Mcavoy in post # 5 regarding that light green wire in the engine harness like mine.
http://67-72chevytrucks.com/vboard/s...d.php?t=589842
Now that wire does not appear in any of the diagrams I've seen. If it's for the TCS where does it go inside the cab?
If it won't hurt anything I'd like to use that wire to power my electric choke.

Re: wiring harness differences
 

In the diagrams I posted, that light green wire is the power wire for the bright headlights. It should have a connector wire that goes to the cluster for the bright light indicator bulb.

I'm surprised that you only have 5 wires on the engine side of the firewall block. but in any case the TCS system didn't come out until late 70 or early 71. There may be some TCS wires in your 71 harness. I don't have a diagram of all the wires in The TCS harness.
There is some debate on the steering column reverse light switch. Some say there isn't one for 3ott but Ray''s post plainly shows one. It may be that they were used on pre 67 models. I can't say for sure but I wouldn't dispute anything Ray says.

What do you have for a column? If it has provision for the NSS then you only have to run a wire from the fuse panel BU light fuse to the NSS, and then run one to the rear of the truck to the lights. You should already have these in the 71` harness.

You can piggyback off of any key on fuse with 10 amp capacity in the fuse panel and run it to the electrical choke. I like the idea of using the wiper fuse since you don't use them unless it's raining. It would be the yellow wire that powers the motor and the washer pump. You could also run a dedicated wire off the IGN UNfused terminal with an inline fuse to the choke. Same with the cigar terminal if you aren't using that. Just be sure that it's key on power so you don't drain the battery.

I'll have to go back and look at your first posts a little harder to see if I missed something.

You have to be sure to match the wires in the 71 engine firewall block with the block inside the cab or things won't work. Even on same year trucks these wires don't always line up with the in cab harness.

Here's a typical engine side harness.



Attachment 1604157





HNY VV

Re: wiring harness differences
 

Many possibilites for things getting changed on old vehicles over 40+ years. I'll get a pic or two of mine and we can compare. Mine has been sitting torn down for 20 years.

Re: wiring harness differences
 

Sarge I snapped a few pics of my 69 harness.
The first ones are of the bkup light switch wires inside the cab and of the bkup light switch mounting point on the 3 ott column. This is temporary as it has an auto trans now.
Next are pics of the wires in the engine side harness of the 69. The light green one I believe is the original coil wire on this 69 with 6 cylinder. In your pic I think it would be the white cloth covered wire.
The last pic is of the engine harness from a 71 for comparison. It also has only 5 wires but it has one short blk/brn wire that mine doesn't have. Obviously there are differences between years and options.