73-87 Chevy _ GMC Trucks > Electrical
1977 K20 Engine Harness
Henry:
Hi EH:
In my previous discussion I first mentioned I had a green wire and connector dangling behind the HEI. Well, it is so old that my notes say that it is either dark blue or dark green...it is probably actually dark blue and is related to the unused electric oil pressure sender. It is a real short exposed wire from the conduit and hangs behind the engine between the HEI and the driver side valve cover. My 1976 Supplemental Manual actually shows it hanging loose on the LF4(400)/LG9(van V8 engine?)/LS9(350) engines but does not describe what it is for.
Regards,
Henry
ehjorten:
Henry and BD...Thanks for your replies. I have an original 1977 Truck Wiring Diagrams book! I am a junky on all of that old documentation. I have Parts and Illustration Books, Assembly Manuals, Wiring Diagrams, etc. on all of my old cars!
I was getting confused on what the difference was between the "Canadian" engine harness and the standard V8 engine harness and what I "should" have.
What I see is that if I was to add the two prong OPS I would need to add a jumper wire to the choke (circuit 901) from the circuit 931 Dk Blu wire. I would need to upgrade the oil tell tale circuit 31 from a 20 ga wire to a 12 ga wire. Then I would need to add the Circuit 300 Orange 12 ga. wire to my engine harness to the other side of the OPS. I then would have to investigate if my dash harness has the necessary wiring in it to function properly. I don't believe I have a choke light anywhere on my dash, so I am not certain what circuit 31 would be going to. I see a 20 ga dk blue 931 wire going to the gauges instrument cluster, but it is a 12 ga dk blue 931 for the idiot light cluster.
I need to get this truck back on the road, so it sounds like a longer term project to do this.
bd:
Unless you wish to adhere to strict "period correct" construction you can dispense with the "Choke" light in the dash. And, you certainly don't need 12-gauge wiring! A pink 18-gauge I+ wire protected by an inline 4- to 5-amp fuse to feed power to the non-grounding 2-prong OPS and an 18-gauge wire in your choice of color (OEM is light blue) from the OPS to the choke heater element will suffice. If the factory dark blue (931) wire dangling from the harness is not connected to an I+ powered bulb in the cluster, don't use it.
Henry:
Hi Eric:
If I am not mistaken, the choke indicator light on the dash cluster would be in either of the two big round gauge faces of your cluster...either the speedo face or the other face which is either a fuel gauge face or tach face depending on your options. It will be at the bottom of the face and be normally blacked out lens so you dont see the writing on it which should illuminate the word "CHOKE" when it gets it is on. It should be a small black rectangular lens that is curved to match the bottom of the gauge face. So if you dont have this someone has swapped out the original dash cluster.
I also think that all C/K-10s through C-30s that had a V8 engine with a Q-jet carb in 1977 had the electric choke and hence should have had the instrument cluster with the choke light. I think 1976 was the last year C/K-20s and 30s with the small-block V8 had the mechanical (divorced) choke and had an instrument cluster without the choke light...all V8 C/K-10s in 1976 had the choke. It was very confusing but it all had to do with the staggered introduction of emissions equipment of the heavier duty trucks.
Regards,
Henry
ehjorten:
Ordered the engine harness from NPD. It was a pretty good representation of the original. The water temp sender pigtail was a little short, but did reach and connected to the sender, just the pigtail looks a little stretched. The black dielectric that they provide to seal the bulkhead connector was a little skimpy and they could have provided another ounce. My stock one was filled-up more and the amount they provided was barely enough. The alternator leads were sufficient in length, but could have been shortened a little. That could be easily fixed. The biggest issue I had, and it is just a bit of a nit, was with the starter leads. The starter leads are long enough that I could clock my RobbMc mini starter so that the solenoid could be pointed down and tucked up near the oil pan (I ended up not doing that), but the starter wire ring terminal was too small to fit over the stud. I ended up cutting off that small ring terminal and putting on a standard small, yellow solderless ring terminal and some good shrink wrap. The new RobbMc mini starter is SO MUCH better than the stock starter! I ditched the metal tube that mounted to the stock starter solenoid for the wire routing. The new starter is so much smaller and the solenoid has much more clearance to my headers in the stock solenoid location, that the wires naturally route far away from the headers. There is no simple way to have that tube connect to the solenoid of the mini starter anyways.
I haven't done anything yet with the choke circuit to try and integrate it with an oil pressure switch, but it is on my to do list. Right now the choke is just getting power off of the coil feed circuit. Glad to have my '77 back on the road!
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