1975 Chevy Vega Fuse Box (extra wires in front)

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Re: 1975 Chevy Vega Fuse Box Wiring Question

Postby robert123 » Wed Apr 06, 2016 4:57 am

spencerforhire "By your voltage readings, it's obvious someone has the pink ignition feed hooked to Bat+ instead of Ign+. That is causing the drop when you hook up the battery. Try disconnecting all that mess at the fusebox and run your own new wire to the HEI."

Hey guys, good news from the front:

I had to find out/trace where those 2 black wires [with the attractive metal splice] went to. Wanted to make sure it was safe.

Sidenote.............. DOES ANYONE KNOW HOW TO REMOVE THE VEGA DASH? Got the dash pad off okay (3 pressure clips on the right); but the main part of the dash (held on by 2 factory Rivets (on the bottom)........ It seems impossible to remove the dash (for access to wiring) unless you drill out the wonderful factory Rivets.

After about 3 hours ........... this is what our team found out:

1) Ignition Switch (on column)-Pink Wire -- 12g, Fat, Pink Wire joins -- like you would expect-- the other wires in the main wiring harness (black tape wrapped bundle). The main wiring harness goes behind the instrument cluster and moves toward the fuse box at the firewall. At the fuse box, the 12g Pink 'Wire goes behind the upper-left corner of the fuse box. (Appears to exit out the front of firewall [firewall junction].) Also there are 3-4 approx. ~16g pink wires that go behind the fuse box with the rest of the wiring harness.

2) 2 Black wires [with attractive metal splice] -- Wow. What a PITA to trace these wires from Gehenna. :censored:
Couldn't remove the entire dash so clearance was difficult -- had to 'adapt and overcome.'
So here's the play-by-play: a) one of the black wires goes about 12" from the metal splice & then is grounded to the metal dash framework with a screw. The other black wire ... follows the main wiring harness.... goes over the top [inside] of the dash ..... down over the rear of the odometer/cable hookup....(where it is reaaaaaaaaaaaaalllllllllllllllllllllyyyyyyyyyyyy tight; had to use mirrors.... wires with hooks etc.) then goes into one of the (approx. 7) Dash Light Sockets. The dash light socket has only a black wire [from Gehenna] and a yellow wire going to it. * At the top of the dash is a stock looking white, dash light socket (with no light) that is taped up to the main wiring harness. (It appears to be the original one.) The light socket with the Black and yellow wire appears to be a new addition (it also had no bulb). So now we know where those 2 black wires go to.

* Do you guys think this whole setup was one of those "Optional Ways to Wire Power to the HEI -- using the IGN terminal?"
And the dash light socket was the resistor?????

Photo shows:

1. Center of photo -- shows the ~ 4" long ~12g Pink Wire coming out to the Bulk Head connector, with a Blue Plastic connector, looping quickly around to the 4" Dark Blue 12g wire.
I was thinking of separating those two wires at the plastic connector -- and running the Pink Wire directly to the HEI?? What about the Dark Blue wire?
2. Red 10-12g wire goes to a fusible link. Anyone know what the Red wire is for?
3. Orange 12g wire -- at center of photo, goes 8" to its black plastic connector on the firewall. Anyone know what that is for? (I'm taking notes on all of these wires;

Thanks a lot.
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1973 Chevy Vega GT Hatchback, stock, 4-speed
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Re: 1975 Chevy Vega Fuse Box Wiring Question

Postby spencerforhire » Wed Apr 06, 2016 6:45 am

Too bad you spent so much time following the factory ground splice in the black wires; it's normal.
Also normal is some of the pinks spliced together behind the fuse box.
Out under the hood, the pink(ignition) spliced into the blue(fuel pump) was probably done to eliminate the OEM oil pressure switch that normally controls the fuel pump. That pink that's presently only running the fuel pump is the best choice to run to the HEI. As a temporary measure, just splice into the joint to power the HEI; If you disconnect the blue, it will not run for long(only until it uses up whatever fuel is in the carb). You can always install a proper oil pressure/fuel pump switch later, once you've got it running properly.
The orange is the heater blower motor power.
The 12g red with the fusible link is the main feed from the battery.

P.S. You don't have to drill out any rivets to remove the dash; it all comes out in one piece. The rivets hold the plastic to the metal brace that goes all the way from side to side.
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"(9.35@146.19)(5.94@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: 1975 Chevy Vega Fuse Box Wiring Question

Postby robert123 » Wed Apr 06, 2016 11:14 pm

spencerforhire wrote:Too bad you spent so much time following the factory ground splice in the black wires; it's normal.
Also normal is some of the pinks spliced together behind the fuse box.
Out under the hood, the pink(ignition) spliced into the blue(fuel pump) was probably done to eliminate the OEM oil pressure switch that normally controls the fuel pump. That pink that's presently only running the fuel pump is the best choice to run to the HEI. As a temporary measure, just splice into the joint to power the HEI; If you disconnect the blue, it will not run for long(only until it uses up whatever fuel is in the carb). You can always install a proper oil pressure/fuel pump switch later, once you've got it running properly.
The orange is the heater blower motor power.
The 12g red with the fusible link is the main feed from the battery.

P.S. You don't have to drill out any rivets to remove the dash; it all comes out in one piece. The rivets hold the plastic to the metal brace that goes all the way from side to side.


The car may have had an electrical fuel pump from one of the earlier owners.
Currently has a mechanical pump on the sbc installed about 2 years ago. Yeah, their is an oil pressure switch on the engine.....but I don't remember any wires going to it.
So use the spliced Pink ignition wire to run the HEI. Then if it runs good, I'll wire in the oil pressure sender.
*Orange wire = heater blower power
*Red 12g with fusible link = main feed from battery.
*Dash comes out in 1 piece (look for mounting bolts on side of dash framework)

Thanks a lot

Here's a photo of what I removed. I cut-spliced the wires in a few places to help removal.
* The other black wire (attractive metal crimp) is still going to the ground on the dash frame.
* The dash light that is removed (in photo) has yellow and black wires going to it.
* The dash light that was unused (taped to the factory wrapped wiring harness) has a yellow-black and yellow wire going to it (white connector or light socket).

Not counting the Red and Pink wire mess going to the fuse box -- did the factory wired it this way (using a dash light socket) as part of the ground for the dash??
Any idea why the tan wire bundle (in photo) is for??
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Re: 1975 Chevy Vega Fuse Box Wiring Question

Postby spencerforhire » Thu Apr 07, 2016 9:10 pm

I can find nothing in any of my H-body wiring diagrams that resembles that mess you removed; it must be something left over from an unknown modification. Or possibly something California only emission related. Either way, don't sweat it; it probably has nothing to do with how the car runs.
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"(9.35@146.19)(5.94@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: 1975 Chevy Vega Fuse Box Wiring Question

Postby robert123 » Fri Apr 08, 2016 3:28 am

spencerforhire wrote:I can find nothing in any of my H-body wiring diagrams that resembles that mess you removed; it must be something left over from an unknown modification. Or possibly something California only emission related. Either way, don't sweat it; it probably has nothing to do with how the car runs.


That's good news.

I didn't want to have to put it back in there...

It's a good car. There are a couple of other bizzaro world mechanical repairs that have been fixed.

It did have a battery shut-off switch (uses a special key). Where one of the battery cables bolted to the switch, the plastic had melted at some point. And 1 wire under the hood seems to have some burn marks. Maybe the fusebox was replaced as a result of a small electrical fire?

Thanks for the advice ........................ I'll wire the Pink wire to the HEI tomorrow. :th:

Will let you guys know how it runs in a day or two.
1973 Chevy Vega GT Hatchback, stock, 4-speed
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Re: 1975 Chevy Vega Fuse Box (extra wires in front)

Postby spencerforhire » Fri Apr 08, 2016 6:33 am

Those shut-off switches with the removable red key are really only good for about 100 amps. Not suitable for use as a battery disconnect in a street or race car.
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"(9.35@146.19)(5.94@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: 1975 Chevy Vega Fuse Box (extra wires in front)

Postby robert123 » Tue Apr 12, 2016 3:14 am

spencerforhire wrote:Those shut-off switches with the removable red key are really only good for about 100 amps. Not suitable for use as a battery disconnect in a street or race car.


Okay, that's good to know.

Good News!

Ok guys, the wire mess in front of the fuse box is gone -- may send it to the Smithsonian [to help future generations}.

1. Rewired the HEI -- like spencerforhire recommended -- ran a new 12g wire (Yellow), weather-proof connector [melt it with a Bic lighter;} from the short Pink wire coming out of Firewall Junction (FJ) to the HEI.......... and the ~ stock, SBC, 4bbl, Started right up.... Idles very good (about 8 min) ...... and Responsive to revs to 1k...2k...3k :mrgreen:
2. The old #2 sensing wire from the alternator went to a 3-way splice (made up of #2 sensing wire; wire to HEI; and then a wire to (FJ).... [the
faded Red, with black dots on it, wire coming out of FJ).
3. Now -- as a quick/temp/perm fix -- ran the #2 to the common "loop-de-loop"..... 4 inches away to the Alternator battery cable stud. (Don't know which wire
coming out of FJ to wire #2 sensing wire to.)


It runs good. It's a stock ... low compression... occasional weekend cruiser.... not a race car.

Photo (with attractive masking tape labels) -- and test light results of Cut wires:
a. "Old wire to HEI" = comes from faded Red wire that goes into (FJ)... has black ink marks every few inches ........ has POWER ... when key is OFF and when ENGINE IS RUNNING
b. "New wire to HEI" = 12g Yellow wire connects to Pink wire... then goes directly to HEI.
c. "Old Pink + Dark Blue" = goes to Dark Blue wire, 4 inches long, into FJ ... has Light Blue crimped connector... was connected to Pink wire coming
out of FJ ....... has NO POWER when key is OFF and when ENGINE IS RUNNING

Any suggestions?
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Re: 1975 Chevy Vega Fuse Box (extra wires in front)

Postby spencerforhire » Tue Apr 12, 2016 6:18 am

The blue wire that you have left disconnected is the electric fuel pump feed. If it ran for 8 minutes, I guess it's unnecessary. lol.
It is acceptable to just leave the large red voltage sense wire hooked to the alternator stud. As long as the small brown "exciter" wire runs to the cluster through the "bat" or "alt" idiot light, that's all you really need to make the alternator function.
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"(9.35@146.19)(5.94@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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1972 Chevrolet Vega Hatchback

Re: 1975 Chevy Vega Fuse Box (extra wires in front)

Postby robert123 » Sun Apr 17, 2016 5:26 am

spencerforhire wrote:The blue wire that you have left disconnected is the electric fuel pump feed. If it ran for 8 minutes, I guess it's unnecessary. lol.
It is acceptable to just leave the large red voltage sense wire hooked to the alternator stud. As long as the small brown "exciter" wire runs to the cluster through the "bat" or "alt" idiot light, that's all you really need to make the alternator function.


Yeah, its got a 4bbl Edlebrock carb, no a/c......... and very Few electrical demands. The small brown exciter wire is connected to the #1 wire on the alternator -- and then goes through the Firewall Junction in the middle.. Took it for a 10 minute drive a few days later........everything works good: engine, ignition is great (responsive), electrical lights. etc.

Okay guys here are 2 concerns:

1) The stock column igniton switch used to start, run, and shut off normally. Now it starts and runs normally ........ but can't shut off the engine ( have to pull #2 sensing wire and the negative battery cable). Since I'd like an ignition kill switch.... how about just cutting into the middle of the Yellow 12g wire that runs to HEI and installing a 30a switch. (That could serve as a kill switch.............. and ignition cut off switch.)

2) Also, the GEN light used to work on the dash ........ now I never see it come on.

Got any suggestions?
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Re: 1975 Chevy Vega Fuse Box (extra wires in front)

Postby spencerforhire » Sun Apr 17, 2016 8:54 am

Like I said in my last post, the "gen" light in the dash is supposed to be wired in series with the brown sense wire to the alternator. It won't shut off if it's just hooked straight to ignition.
If you can live without the idiot light, you could just put a diode in the sense wire instead. Stripe toward the alternator.
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"(9.35@146.19)(5.94@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
User avatar
spencerforhire
 
Posts: 2404
Joined: Mon Jul 03, 2006 9:02 pm
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1972 Chevrolet Vega Hatchback

1975 Chevy Vega Fuse Box SUCCESS -- plus Doggy Free Love.

Postby robert123 » Mon May 23, 2016 1:18 am

spencerforhire wrote:Like I said in my last post, the "gen" light in the dash is supposed to be wired in series with the brown sense wire to the alternator. It won't shut off if it's just hooked straight to ignition.
If you can live without the idiot light, you could just put a diode in the sense wire instead. Stripe toward the alternator.


Approx. 3 weeks later ......

Okay, been busy with work -- and other wholesome activities that would make the Pope proud.
Yes, the diode is a good and normal idea -- many websites recommend that. (The diode is a 1-way valve for electricity. It will prevent current from going back to the ignition switch and causing a "run on" condition when the ignition is turned off.) The 3" long Radio Shack diode (or rectifier diode; part # 1N4001 or 2761101; 30 amp) is only a few bucks (see attractive photo). If you install it (like mentioned before) put the stripe or band pointed toward the alternator. The #1 wire (ignition wire) gets the diode -- to prevent current "back flow."

But, I really don't like soldering.... and I wanted another kill switch to deter smelly [and non-flossing] thieves.
So............ finally came up with the time.... and a good idea ........... with a Bonus Idea -- which NASA may be calling me about.

Here's what I did: 1) I cut the wire to the HEI in half at the firewall (about 18" each way). 2) Then, inside the car, with strength, internal fortitude -- and a hearty "Okay" from Toto (my carnivorous Pit Bull) -- I hooked about 10 feet of #12 gauge wire; to a 20 amp fuse [before the switch to protect it] then
onto the 30 amp switch [lighted -- looks cool switch]. This effectively, gives me about "2" additional "Kill Switches" [which makes my heart all fuzzy]. Depending
on the degree of threat (possible car theft] I can just flip the switch....... or remove the hidden fuse..... and help deter the unhygienic thieves. :mrgreen:

Bonus Idea: an accidental bonus is that the ignition kill switch allows for Priming of the Engine Oil in winter months (or after sitting a long time). You can have the 30 amp ignition switch off....... then crank the engine over for approx. 4 seconds. This will let you Fully lubricate everything inside your SBC ......... then flip the switch .... and your engine will fire up -- all lubricated & full of mechanical-based J-o-y.

To celebrate... I took Toto to the local Dog Park for some doggy "free love" dating opportunities. (Had Whitney Houston - "You Give Good Love" playing on his headphones -- worked great.)

Thanks for all of your help -- the car is running good !
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