Question (wiring under hood)

[SEVEND2]

Ok, I been working on my truck for a few years now, under the hood, I got a problem where i forgot to label or labels fell off. so here it goes.

on the upper left fire wall above the main wire harness, there is a small round wire harness with 4 or 5 wires in it, I dont know where they go under the hood, One is a hmm 10 or 12 gage Main red wire from a Unfused slot on fuse box, (the others are about a 16 gauge type wire )a brown with white stripe has a end connector (i think it hooks up to the other harness) near the brake booster, also a dark blue and a brownish color, and a light tan color that goes to the brake sensor

Please help, I dont have any one around that has a truck like this to check these, I hope some one can guide me.

Thanks:

[bpmcgee]

72,

I think that harness is the wiring harness for the emissions control relays that are just above and outboard of the main firewall plug.

Do you still have those relays? if so, I'll look up the wiring pattern for you in my manual.

Brian

[SEVEND2]

The Wires go to a silver colored box right above the fuse box under dash,

the larger red wire is unfused

mose of the wires are long enough to reach from the left side to the right side of the fire wall.

I dont know if the silver box is a realy box or not

[bpmcgee]

What year and type is this?

[SEVEND2]

1972 Chevy,
C-10 longbed,
Smog and etc removed.

[Hooter]

I have that relay box in my truck and it used to control the dual battery setup, there is another almost identical box that controls the horn, I dont know what your wires do, but I am willing to bet that those wires are for the tcs (transmission controled spark) system. One wire goes to the tranny, two other wires go to the little round thing that goes inline with your vacum advance vacum line and the other wires go to the soleniod

[bpmcgee]

72,

I don't have a wiring diagram from a 72. All my info on 71's lead me to a couple of possible conclusions:

1) It says in my emissions manual that vehicles equipped with A/C would have had an anti-dieseling solenoid under the dash. Get this -- the purpose was to ENGAGE THE A/C COMPRESSOR for 3 seconds AFTER the ignition was turned off. So, it would need a hot wire to an unswitched source, and wires that ran into the engine compartment. Unfortunately it doesn't show a diagram of this, nor is it included in my other diagrams.

2) It could be the CEC (Combined Emissions Control) relays. On my 71, though, these are above and to the right of the firewall harness. These include a brown, a black, a light blue, a dark blue, and a red wire. I think this is your best bet.

The only way to tell for sure would be to buy either a factory service manual for 72s or get the factory 72 emissions control supplement.

Brian

[SEVEND2]

Thanks
for your help, it gives me a great place to start. I think it was for the old Quadra-junk carb and the emmissions too.
I will follow up and through.

Thanks again!