Turn signal wiring/switch theory confusion - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jds8086 · 10-29-2018, 06:53 PM

Working on a '71 C20, the owner (a friend) replaced about every wire in this truck and most everything seems to be working, but we are having troubles figuring out the front side markers. The diagram we have shows that one wire goes to the running lights (brown) and the other to the turn signal wire for whichever side it is on (LT blue / blue). Things aren't working as they should and all i'm really after is for someone to explain how this setup is supposed to operate. For instance if you had your parking lights on, and turned on the turn signal, how would the side marker flash if it has constant 12v on one wire (parking light, brown wire) and alternating 12/open on the turn signal wire? If i understood how it worked i could probably get it figured out but it just isn't making sense to me. Any help is appreciated.

Brentwe · 10-29-2018, 09:26 PM

Someone may come on with wiring diagram and a better explanation, but here is my understanding.
Apply power to the side light and it will ground thru the signal light filament. When power is applied to the signal light , the side marker will see 12v on both sides, therefore it will not light up as there is no voltage differential so no current flow.

jds8086 · 10-29-2018, 09:59 PM

Quote:

Originally Posted by Brentwe

Someone may come on with wiring diagram and a better explanation, but here is my understanding.
Apply power to the side light and it will ground thru the signal light filament. When power is applied to the signal light , the side marker will see 12v on both sides, therefore it will not light up as there is no voltage differential so no current flow.

Ok my lightbulb lit (no pun intended). I hadn't considered the fact that there is a path to ground through the other filaments in the front running light/indicator. I think i can figure it out from here. I do wonder though how this setup will work with all LED's as this is what he is using. Thank you for clearing this up!

**HO455** · 10-30-2018, 11:39 AM

Here is a description of how flashing marker lights work.

https://www.danielsternlighting.com/...rkerflash.html

10-29-2018, 06:53 PM	#1
jds8086 Registered User Join Date: Oct 2018 Location: KS Posts: 2	Turn signal wiring/switch theory confusion Working on a '71 C20, the owner (a friend) replaced about every wire in this truck and most everything seems to be working, but we are having troubles figuring out the front side markers. The diagram we have shows that one wire goes to the running lights (brown) and the other to the turn signal wire for whichever side it is on (LT blue / blue). Things aren't working as they should and all i'm really after is for someone to explain how this setup is supposed to operate. For instance if you had your parking lights on, and turned on the turn signal, how would the side marker flash if it has constant 12v on one wire (parking light, brown wire) and alternating 12/open on the turn signal wire? If i understood how it worked i could probably get it figured out but it just isn't making sense to me. Any help is appreciated.

10-29-2018, 09:26 PM	#2
Brentwe Registered User Join Date: Aug 2018 Location: Chetwynd, BC Posts: 58	Re: Turn signal wiring/switch theory confusion Someone may come on with wiring diagram and a better explanation, but here is my understanding. Apply power to the side light and it will ground thru the signal light filament. When power is applied to the signal light , the side marker will see 12v on both sides, therefore it will not light up as there is no voltage differential so no current flow. __________________ Brent W 66 short step 4 x 4

10-30-2018, 11:39 AM	#4
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,350	Re: Turn signal wiring/switch theory confusion Here is a description of how flashing marker lights work. https://www.danielsternlighting.com/...rkerflash.html __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

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