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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Jul 2007 Posts: 6 New Guy | | New Guy Joined: Jul 2007 Posts: 6 | Hi guys!
I'm in the process of getting my '66 C10 short/fleetside up & running after swapping out the 250 six/3-on-the-tree manual for a 350/TH700R4 and an automatic column from a '78 Chevy van. I've done all the finagling to get the auto column physically mounted & hooked up in the truck, so now it's mostly down to the wiring and a few tidbits.
I have the '66 C10 wiring schematic, but for the life of me haven't been able to find the schematic for the '78 van, which has 8 wires coming out of it vs. the 7 from the '66 harness. Presumably one matches up the wire colors from one harness to the other, and I know the extra (brown) wire is probably for the 4-way flashers, but I want to be sure I do this correctly.
How does one go about hooking up the 4-way flashers on a truck that didn't come with them from the factory? Have any of you done a similar swap, or know a good place to find the wiring schematic for a '78 G10?
Here's what I have so far:
1966 C10
Purple (fuseblock - 12v+ input, I believe)
Black (horn)
Dk. blue (RH front park lamp)
Lt. blue (LH front park lamp)
White (stoplight switch)
Dk. Green (RH tail light)
Yellow (LH tail light)
1978 TS switch
Black
Lt Blue
Dk Blue
Brown
Purple
Yellow
Green
White
Also, the backup light switch on my column was busted when I got it from the wrecking yard, so I need to replace that as well, but I'm not having much luck finding one online. Any suggestions?
The flasher knob thingie was also AWOL when I picked up the column, so I need that too, but I'm not sure what it looks like. Do any of you have a picture of a similar setup on your trucks? It looks like it's supposed to slide sideways into a slit on the switch itself, and then operates by being pulled out/pushed in?
One last question: I bought a Lokar shift linkage kit, which contains a "cut to length" ss rod and a couple of heim joints at either end. Turns out that rod is 1-2" too short for my truck! Since it's threaded on one end only I suspect I'm going to have to have a replacement custom made, unless anyone has any ideas for me.
Thanks!
Brad | | | | | Joined: Jan 2007 Posts: 220 Shop Shark | | Shop Shark Joined: Jan 2007 Posts: 220 | I put a 71 column in mine. I'm thinking that it should be the same as yours. If so, I think you are on track.
However I hesitate to make any specific comment on yours as I do not know what the 78 wiring schematic specifically looks like.
You should be able to go to your local library and get a copy of the van schematic.
For your backup light/neutral safety switch it should be a low cost item from any local parts store. With it in hand, it should be clear how it operates. Assuming it is the same as my 71, it is a slide switch operated from a tab inside the column (should attach on the shaft near the firewall.
Flasher knob, try looking at an online parts catalog (much like you find them for your 66) and see if they sell them seperatly. It may be that yours is broken off and can be simply replaced. Then again you may need to replace the whole turn signal switch.
Last question, not sure here. In mounting the column you don't have it too far back do you? I'm wondering if you mounted it so that the bolts lined up and it really needs to be farther forward?? Be sure that the backup light/neutral safety switch will attach at its location. | | | | | Joined: Jul 2007 Posts: 6 New Guy | | New Guy Joined: Jul 2007 Posts: 6 | Thanks Rusty64! Yep, that b/up switch is slider type that mounts on the top of the column down near the firewall. I'll try the local parts store - I was just surprised such a seemingly common item wasn't easier to locate at the online stores I've used in the past! I'll have to make a junkyard trp this coming weekend to see if I can find one of those pesky flasher knobs too... I did mount the column pretty far back, mostly because at 6-4 I'm a big guy and can use the extra room!  Compared to the stock '66 column, the steering wheel seems to be pretty close to the same position. I had to come up with my own mounting location, because the '78 column didn't match up to the '66 bracket (as far as existing mounting bolt holes, etc.). I guess that may have complicated things as far as the shift linkage goes - but I've come this far so I'm sure I'll figure something out. The parts I already have are very close to working - just need a longer rod, and that's the easy part! Anyway, I worked on it some more tonight and the wiring's almost done - just have to figure out that brown wire from the TS switch now! Brad | | |
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