Firewall wire identity help
 

I just picked up a really original 72 402 c20 out of cali for my new daily and I found these 2 wires one of which snipped and the other disconnected. I looked at wiring diagrams and can't see it cleanly so I was hoping someone may be able to provide some insight.

Re: Firewall wire identity help
 

Looks like the blue wire for the NL2 optioned extra fuel tank sending unit to the dash selector switch.

Re: Firewall wire identity help
 

thank you that makes complete sense it was a factory dual tank truck(no wonder my c10 doesn't have it) now I just need to figure out the connector above it.

Re: Firewall wire identity help
 

Flip for ya.

Attachment 2436243

Re: Firewall wire identity help
 

Does your truck have a new style alternator? The wire looks white with a black stripe. Here is a link to the wiring diagram.

https://67-72chevytrucks.com/vboard/...d.php?t=185856

Re: Firewall wire identity help
 

yes it dose

Re: Firewall wire identity help
 

First, really poor memory, but I seem to recall the plug is 12v. I can't recall if it was switched or not. It was on my 72 GMC and also the replacement harness. I did not need so I eliminated out of the harness and used the pin for something else. I never was able to identify what option it was for. I wondered if it was for a cruise control or simply a switched +12v tap.

Re: Firewall wire identity help
 

Makes perfect sense to have ordered the dual tank option with the big block.

Re: Firewall wire identity help
 

Black with the white stripe is probably one of the wires for the Ammeter. If you have a newer alternator or voltmeter that wire and heavy black no strip wire are not really needed.

Re: Firewall wire identity help
 

Are you sure that wire is black with white stripe? My ‘70 has a brown with white stripe wire with that connector in the same location. I have kid found a wiring diagram that shows this wire.

Re: Firewall wire identity help
 

I know on mine it is black with white (and the black) on firewall side, but on the inside to gauge cluster it is brown to the actual ammeter gauge Try and trace the wire to the core support, you should come across an inline fuse if it is the wire for the ammeter. On my 70 (and on diagram) the black/white was drivers side, solid black ran to passenger side.