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Ranger6202 · 02-14-2012, 11:08 PM

Got a question for ya. I've just about got my wiring all done. Was wondering how the check engine light wire works coming out of the PCM? Does it constantly supply 12v or a ground and then interrupts it, or vice versa?
I found a mystery plug going into my firewall that has 2 plain yellow wires, one yellow black stripe wire and a solid black wire. When i let the black wire hang free, my check engine light comes on. But when i put it to 12v or ground, it goes out, so i'm assuming this used to be a switch or something that ran off the carb or diesel motor somewhere between the two engines that have been in this truck. I even went to the junk yard and went through about 6 old chevs/gm's and they didn't have this plug. I'll try and get pics tomorrow if i remember.

02-14-2012, 11:08 PM	#29
Ranger6202 Registered User Join Date: Dec 2011 Location: Lyman Wyoming Posts: 109	Re: lq4 6.0 swap into '85 Crew Cab Shorrbed Got a question for ya. I've just about got my wiring all done. Was wondering how the check engine light wire works coming out of the PCM? Does it constantly supply 12v or a ground and then interrupts it, or vice versa? I found a mystery plug going into my firewall that has 2 plain yellow wires, one yellow black stripe wire and a solid black wire. When i let the black wire hang free, my check engine light comes on. But when i put it to 12v or ground, it goes out, so i'm assuming this used to be a switch or something that ran off the carb or diesel motor somewhere between the two engines that have been in this truck. I even went to the junk yard and went through about 6 old chevs/gm's and they didn't have this plug. I'll try and get pics tomorrow if i remember.