needing some underhood wiring help on a 72 vega

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needing some underhood wiring help on a 72 vega

Postby 72quick4you » Sun Oct 25, 2015 2:41 pm

So I bought this car with the v8 swap already in and trying to figure out my aternator wiring. The battery post on it is wired to a block on the firewall on the drivers side that has other wires going to it. What is this block? Tried to post a pic but I need to shrink the size. Thanks for any help
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Re: needing some underhood wiring help on a 72 vega

Postby cjbiagi » Sun Oct 25, 2015 4:26 pm

It sounds like someone just added a convenient block for a 12 volt source. Usually the + battery cable goes to the starter and other wires may tap off of that.
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Re: needing some underhood wiring help on a 72 vega

Postby spencerforhire » Sun Oct 25, 2015 5:19 pm

Didn't the early cars use the horn relay under as a bus point?
The "fleet"-
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(9.45@146.19)(6.01@117.28 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....

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Re: needing some underhood wiring help on a 72 vega

Postby 72quick4you » Sun Oct 25, 2015 8:24 pm

I'm not sure, I don't know much at all about these cars and tried to find an underhood wiring diagram without much luck.
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Re: needing some underhood wiring help on a 72 vega

Postby robert123 » Sun Oct 25, 2015 8:58 pm

72quick4you wrote:So I bought this car with the v8 swap already in and trying to figure out my aternator wiring. The battery post on it is wired to a block on the firewall on the drivers side that has other wires going to it. What is this block? Tried to post a pic but I need to shrink the size. Thanks for any help


free photo editing @ lunapic.com; then click on resize

Yeah, like spencerforhire says, it sounds like the Horn Relay (a bus or hotspot). The Horn Relay sits on top of a bunch of wires (my free download pdf
1972 Vega Wiring Manual says thats the Fuse Panel ASM)
http://vintage.mitchell1.com/PClubData/ ... 972dwd.asp
(have to do the email regirstration thing ------- but great free pdf manuals.)

Photo of 1972 Vega Horn Relay:
Attachments
vega horn relay.png
vega horn relay.png (66.79 KiB) Viewed 336 times
1973 Chevy Vega GT Hatchback, stock, 4-speed
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Re: needing some underhood wiring help on a 72 vega

Postby 72quick4you » Tue Oct 27, 2015 2:26 am

That's it. No way there should be a wire running from that post to the battery post on the alternator right?
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Re: needing some underhood wiring help on a 72 vega

Postby spencerforhire » Tue Oct 27, 2015 6:40 am

The post on the horn relay is connected to the same red wire that goes on the alternator post, but normally there's a splice buried in the harness. If the fusible link at the starter(where this red wire normally connects to the battery cable) has burned out, then someone may have run it directly as a band-aid solution. Or my diagram could be wrong and it's supposed to go there. Either way, it's not "wrong".
The "fleet"-
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(9.45@146.19)(6.01@117.28 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....

Visit http://www.spencerforhire.ca
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Re: needing some underhood wiring help on a 72 vega

Postby avewhtboy » Wed Oct 28, 2015 11:09 am

It may be a resistor used to "excite" the alternator if you are running an "idiot light" rather than a guage. Not having one
is a sure way to burn up an alternator.
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Re: needing some underhood wiring help on a 72 vega

Postby 72quick4you » Wed Oct 28, 2015 9:21 pm

Well now I'll have to dig a little deeper. The only wire on the horn relay post us a 12 gauge wire that runs to the battery post on the alternator. The battery is in the back and the hot runs to the starter. There's a switch in the dash that is wired to the field terminal on the alternator and it kills the charging system when switched.
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Re: needing some underhood wiring help on a 72 vega

Postby spencerforhire » Thu Oct 29, 2015 6:54 am

Whatever previous owner did the V8 swap in your may not have had a complete grasp of the workings of a charging system. Having a switch to shut off the alternator is kind of silly. At full output, even a beefy 100 amp alternator only eats up a couple of HP. The trade off is not worth it; in a race car, the important electrical components like ignition box, fuel pump and water pump will perform better and last longer at 14.5 volts than they will at 12.
Does the car run and charge the battery(with the switch on)? If you take the switch out and re-connect the wire to the idiot light in the cluster, you should be back to normal.
The "fleet"-
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(9.45@146.19)(6.01@117.28 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....

Visit http://www.spencerforhire.ca
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Re: needing some underhood wiring help on a 72 vega

Postby Monza Harry » Thu Oct 29, 2015 2:30 pm

spencerforhire wrote:Whatever previous owner did the V8 swap in your may not have had a complete grasp of the workings of a charging system. Having a switch to shut off the alternator is kind of silly. At full output, even a beefy 100 amp alternator only eats up a couple of HP. The trade off is not worth it; in a race car, the important electrical components like ignition box, fuel pump and water pump will perform better and last longer at 14.5 volts than they will at 12.
Does the car run and charge the battery(with the switch on)? If you take the switch out and re-connect the wire to the idiot light in the cluster, you should be back to normal.

Remember Spence back about 15/20yrs. ago that was a popular modification, a lot of ass u me ing going on. I doubt anybody ever tested their claims of drag strip glory, for a pure drag car the fad that went next does help a little but I doubt a stop watch would pick it up, and that is the oversize alt. pulley, but it will help make the alt. last longer. If I remember correctly the Alt. runs at approx.. 3X crank speed, varies slightly with pulley and accessory choices from the factory set-up. Harry
I'm not a hoarder I'm a preservationist 78 Monza Spyder (Soon To Be 2+2 with Spoilers)
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Re: needing some underhood wiring help on a 72 vega

Postby spencerforhire » Thu Oct 29, 2015 6:32 pm

On my drag car, I have a 6" crank pulley and 5" alternator pully. As a result, the alternator only runs slightly faster than crank speed, which under power only varies from 5500-7500rpm. I may swap to a 4" one on the alternator because it doesn't hit 14.5 volts until about 1800rpm.
The "fleet"-
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(9.45@146.19)(6.01@117.28 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....

Visit http://www.spencerforhire.ca
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Re: needing some underhood wiring help on a 72 vega

Postby zeke » Mon Nov 09, 2015 11:00 am

Alternators are designed to run at 2.5 times the crank speed.
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Re: needing some underhood wiring help on a 72 vega

Postby spencerforhire » Wed Nov 11, 2015 6:29 pm

2.5x crank speed on a street car(average operating rpm of 2000 -3000) would be 5000-7500 rpm at the alternator. In my drag car with it's 5500 stall converter and 7500 shift point, I guess I'm right in the ballpark with my underdrive pulley.
The "fleet"-
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(9.45@146.19)(6.01@117.28 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....

Visit http://www.spencerforhire.ca
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Re: needing some underhood wiring help on a 72 vega

Postby zeke » Wed Nov 11, 2015 6:33 pm

Exactly! Under drive pulleys are for real race cars, not street cars.
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