70 C20 ignition switch wiring

[DEESTER157]

I’ve got a 70 C20 and I am having to replace my ignition switch, spacer, tumbler, bezel nut and ignition switch connector with pigtail. Im fairly sure how this is wired but I just want to make sure I’m correct about the two green wires and the small red wire. My pickup has actual gauges and not dummy light so I’m thinking this is why I do not have green coming from my dash. Is this right? Also I think the red is batt but the pigtail I bought has a big red and a small red wire. There is only one big red wire from my truck. Do I need to hook both red from my pigtail to the one red from my dash? Besides these, all other wires on pigtail match up (purple=purple) (pink=pink) (large brown, small brown= large brown, small brown white stripe) (2 small brown=2 small brown). Can someone please confirm I am right about all these and let me know what to do with the small red and two greens? Thanks

[VetteVet]

Originally Posted by DEESTER157

I’ve got a 70 C20 and I am having to replace my ignition switch, spacer, tumbler, bezel nut and ignition switch connector with pigtail. Im fairly sure how this is wired but I just want to make sure I’m correct about the two green wires and the small red wire. My pickup has actual gauges and not dummy light so I’m thinking this is why I do not have green coming from my dash. Is this right? Also I think the red is batt but the pigtail I bought has a big red and a small red wire. There is only one big red wire from my truck. Do I need to hook both red from my pigtail to the one red from my dash? Besides these, all other wires on pigtail match up (purple=purple) (pink=pink) (large brown, small brown= large brown, small brown white stripe) (2 small brown=2 small brown). Can someone please confirm I am right about all these and let me know what to do with the small red and two greens? Thanks

The small red wire is used to feed the fuse panel for the key off stuff, Hazards stop light dome light cigar lighter etc. Not all the harnesses had it. They use a wire off the cab junction. See the diagram where the red wires join. One feeds the horn relay one feeds the key switch. one feeds the fuse panel and one feeds the headlight switch.





The two green wires are really just one wire from the engine temperature sending unit to the dash cluster light for the temperature heat light in the idiot light clusters. it is grounded by the ignition switch when the start position is selected to test the light in the cluster.
The gauge clusters didn't have the temperature light so the two green wires are not needed and can be taped off.

The two small brown wires are for the brake warning light in the cluster and they also test the brake warning light when the key is turned to start. You will need to keep those in either cluster.

the larger brown wire with the small brown/yellow stripe is the accessory feed wire to the fuse panel and the small brown/yellow stripe wire is the exciter wire for the alternator. It runs through the firewall block to the external voltage regulator on the radiator mounting core by the left headlight. On the engine side of the firewall it becomes a solid brown wire 16 ga.

Purple is the starter solenoid feed wire. And the pink is for the ignition coil and fuse panel feeds.

[DEESTER157]

Ok awesome! Thanks for the explanation and wiring diagram. I will look again and see if maybe the smaller red wire is tucked up in the dash somewhere and maybe I didn’t see it (just want to make sure). So I’ll get rid of the 2 green and if I do not find a small red then I just won’t be able to use cig lighter, dome light, ect when my key is off right? And I will not hook the small red from the pig tail to anything. So I’ll tape off the 2 green and 1 small red right? Just want to make sure I’m clear on this. Electrical stuff is not something I’m really good at! Thanks

[VetteVet]

Originally Posted by DEESTER157

Ok awesome! Thanks for the explanation and wiring diagram. I will look again and see if maybe the smaller red wire is tucked up in the dash somewhere and maybe I didn’t see it (just want to make sure). So I’ll get rid of the 2 green and if I do not find a small red then I just won’t be able to use cig lighter, dome light, ect when my key is off right? And I will not hook the small red from the pig tail to anything. So I’ll tape off the 2 green and 1 small red right? Just want to make sure I’m clear on this. Electrical stuff is not something I’m really good at! Thanks

If you look at the diagram of the fuse panel above you can see a large red wire coming from a tee into it. This is a feed wire for the key off stuff so you should still get to use the stop light switch and the dome light and the cigarette lighter.
The pink wire next to it is the cluster feed fuse power wire that feeds the fuel gauge and the temperature gauge. I think they might have used the small red wire in the later model trucks so you may not need it anyway.

[DEESTER157]

Ok I see. Man those diagrams are confusing. I’m kinda illiterate on most wiring and wiring diagrams. I guess I’ll just tape off the small red wire unless I need to connect both small and large red wires from my pigtail to the one large red wire from my truck? Not sure what that would do. Sry to keep going on about it and I really appreciate all your input!

[DEESTER157]

Should I hook both small and big red from pigtail up to my one big red from the truck or should I just hook up the big red wire and tape the small one? Thanks

[howell57]

Just put a new L83 into my 72 C10 and had the harness re-worked. Trying to find the wire out of the firewall that is only hot during cranking. Have the purple wire correctly wired, but can't find wire that is hot only when cranking or in start position. It was suppose to be so simple-two wires?

TKX

[Fbks_Cruiser]

I just did this yesterday. I taped up the small red wire to save if I ever want a +12v always hot for some accessory. I also did not need the green leads as I have a gauge cluster, just taped em.

[DEESTER157]

Ok good deal. What year is your pickup and can you still use your dome light, cig lighter or anything else when your key is off? I’m guessing you only had the one big red wire from you truck right? Thanks

[Fbks_Cruiser]

Yes, just the one big red wire. Dome light and cig lighter work with key off. Radio works in accessory position. Basically everything works as it should.

I was fixing a fubar by the previous owner. All is good now.

1972 GMC k2500

Those ignition switch pigtails are made for multiple years/applications. Not surprising that there may be some unused leads. I checked against this wiring diagram to ensure which wires I needed.

[DEESTER157]

Great! Ya I’m dealing with a fubar myself as my whole ignition, switch and all was robbed out of my truck. I feel pretty good about wiring it up now. Just waiting on my ignition switch spacer to come in and I’ll tackle this project. Great info and I really appreciate all your help👍🏻