Electrical Questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

danho · 03-02-2004, 01:18 AM

OK, guess I should have taken better notes when I took this thing apart but oh well.
There's a RED and a PURPLE wire coming from the engine compartment side of the firewall and I need to know what these connect to. Also the red wire is split into two wires at the end of the wiring gutter. And last, where is the best place to hook up the negative battery cable to get the best ground? BTW this is on my 72 K20 with HEI.
Thanks again, Dan.

Longhorn Man · 03-02-2004, 01:29 AM

The only purple wire I can think of under the hood goes to the S terminal on the starter...it is the 'start wire'.
I like grounding the caable directly to the block, some will say through the acc brackets, but I prefer a straighter route to the starter.
Actually, i wish GM made provisions to bolt the neg cable to the starter like on big trucks.

danho · 03-02-2004, 01:35 AM

That helps, but any idea on the red wire that is split in two? And there are 2 small posts on the starter, which is which?
Thanks, Dan.

Razor454 · 03-02-2004, 01:45 AM

If the red wire comes out of the firewall, then it should go to your HEI distributor. There should be a plastic tips that goes to it, this plastic tip should have two slots in it. If this is not it please post a pic. and I will look at my wiring to try to match it up.

Longhorn Man · 03-02-2004, 02:01 AM

Quote:

If the red wire comes out of the firewall, then it should go to your HEI distributor

Razor454, kinda hard to say that when the HEI isn't a stock piece. Every single 67 - 72 with HEI is an owner add on, so there is no tellin how whom ever wired it.
As for the 2 posts on the starter, one will have an S, the other will have an R. The purple wire goes to the S. (remember it as S for start, and R for remote, the old points set up used the R terminal to relay 12 volts to the coil while starting)
What part of the engine compartment is the red wire at? There are a few of them under there...I am wondering if it is the one to the back of the alt. (are you completing an engine swap here)

danho · 03-02-2004, 02:23 AM

Thanks for all the relpies guys maybe these pics will clear things up. This is the purple wire I was talking about.

danho · 03-02-2004, 02:25 AM

The red wire, looks like a dirty red or a similar color. This one splits in 2 at the end of the wiring gutter.

danho · 03-02-2004, 02:26 AM

A shot of the firewall where they originate.

danho · 03-02-2004, 02:30 AM

Oh and Longhorn, these are separate from the alt wiring. And I am installing a new motor, if I get this figured out I'll be able to fire it tomorrow night.
Gotta go cut my fingernails now.
Thanks guys, Dan.

Razor454 · 03-02-2004, 02:54 AM

Just like longhorn said the purple wire goes to your starter, it should go on the S post. As for the red wire, you are right it could go to anything. This is one of the reasons why I ripped all of my wiring out and redid it with a Painless wiring kit.

Sweet72 · 03-02-2004, 03:30 AM

That red wire should have a black stripe along it if it's the resistor wire for the orig. points dist., it then splits at a splice and goes to the starter and coil + terminal. If this is the wire you're talking about, then you should replace the "red/blk resistor wire with a multi-strand 18-20 gauge copper wire, and run it directly to the coil + term. so your coil (if using an aftermarket HEI w/separate coil) will get a full 12 volts all the time, and eliminate the yellow wire going to the starter. The resistor wire was used to drop the voltage to the coil (after engine start) to about 8 volts to extend the life of the points.

SS55 · 03-02-2004, 03:37 AM

Near as I can tell from the position and the "dirty red" description, it looks like it is the WHT/ORN & PPL wire. If it is original, that wire goes from the junction block and splits above the distributor into two yellow wires. One going to the starter solenoid and the other to the ign coil. I believe the WHT/ORN & PPL is a resistance wire used to limit the voltage to the original ign coils. Not good for your HEI as it will require a full 12 volt source. You could use a voltmeter or a test-light and see if you have voltage present with the key in the on position and crank position to help identify its use.

Darrell

danho · 03-02-2004, 11:33 AM

So the red wire does NOT need to be split in 2? Just relpace if with a new wire and run it to the HEI? And to replace it, do I splice it as close to the junction block as I can or do I need to feed a new wire through the firewall and replace the whole thing?
Dan.

SS55 · 03-02-2004, 12:01 PM

You are correct, it does not need to be split. The cleanest solution would be disassemble the firewall plug and replace the wire and contact with a new wire going to your HEI. You can splice it close to the plug and achieve the same effect as that will replace the resistance wire and give you 12 volts to the HEI.

Darrell

lloyd k · 03-02-2004, 03:53 PM

i have a 472 cadillac in my 67,it has hei- replaced the resistor wire,put an a internially regullated altenator,did away with the external voltage regultor,i have all my factory guages hooked up except the amp guage.wounderng what wire coming out of the firewall should hook to what ?i think it is a brown wire from the schematics that i have ,not sure ? thanks much lloyd k

Sweet72 · 03-02-2004, 04:12 PM

ammeter wires? Not sure exactly what you're asking...

lloyd k · 03-02-2004, 04:58 PM

what wire comeing out of the firewall to power ampmeter guage ? thanks lloyd k

**john** · 03-02-2004, 07:32 PM

LLoyd K There is a black and a black/w wires for ammeter with 4 amp fuses. see diagram.

Blue_71 · 03-03-2004, 01:50 AM

isnt there a red wire that splits in two to go to the junction block by the fender and to the voltage regulator?

03-02-2004, 01:18 AM	#1
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	Electrical Questions OK, guess I should have taken better notes when I took this thing apart but oh well. There's a RED and a PURPLE wire coming from the engine compartment side of the firewall and I need to know what these connect to. Also the red wire is split into two wires at the end of the wiring gutter. And last, where is the best place to hook up the negative battery cable to get the best ground? BTW this is on my 72 K20 with HEI. Thanks again, Dan.

03-02-2004, 02:23 AM	#6
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	Thanks for all the relpies guys maybe these pics will clear things up. This is the purple wire I was talking about. Attached Images

03-02-2004, 02:25 AM	#7
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	The red wire, looks like a dirty red or a similar color. This one splits in 2 at the end of the wiring gutter. Attached Images

03-02-2004, 02:26 AM	#8
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	A shot of the firewall where they originate. Attached Images

03-02-2004, 02:54 AM	#10
Razor454 Registered User Join Date: Feb 2004 Location: Stokesdale, North Carolina Posts: 341	Just like longhorn said the purple wire goes to your starter, it should go on the S post. As for the red wire, you are right it could go to anything. This is one of the reasons why I ripped all of my wiring out and redid it with a Painless wiring kit. Last edited by Razor454; 03-02-2004 at 03:02 AM.

03-02-2004, 01:29 AM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	The only purple wire I can think of under the hood goes to the S terminal on the starter...it is the 'start wire'. I like grounding the caable directly to the block, some will say through the acc brackets, but I prefer a straighter route to the starter. Actually, i wish GM made provisions to bolt the neg cable to the starter like on big trucks.

03-02-2004, 01:35 AM	#3
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	That helps, but any idea on the red wire that is split in two? And there are 2 small posts on the starter, which is which? Thanks, Dan.

03-02-2004, 01:45 AM	#4
Razor454 Registered User Join Date: Feb 2004 Location: Stokesdale, North Carolina Posts: 341	If the red wire comes out of the firewall, then it should go to your HEI distributor. There should be a plastic tips that goes to it, this plastic tip should have two slots in it. If this is not it please post a pic. and I will look at my wiring to try to match it up.

03-02-2004, 02:30 AM	#9
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	Oh and Longhorn, these are separate from the alt wiring. And I am installing a new motor, if I get this figured out I'll be able to fire it tomorrow night. Gotta go cut my fingernails now. Thanks guys, Dan.

03-02-2004, 03:30 AM	#11
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	That red wire should have a black stripe along it if it's the resistor wire for the orig. points dist., it then splits at a splice and goes to the starter and coil + terminal. If this is the wire you're talking about, then you should replace the "red/blk resistor wire with a multi-strand 18-20 gauge copper wire, and run it directly to the coil + term. so your coil (if using an aftermarket HEI w/separate coil) will get a full 12 volts all the time, and eliminate the yellow wire going to the starter. The resistor wire was used to drop the voltage to the coil (after engine start) to about 8 volts to extend the life of the points. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction. Last edited by Sweet72; 03-02-2004 at 03:55 AM.

03-02-2004, 03:37 AM	#12
SS55 Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 62	Near as I can tell from the position and the "dirty red" description, it looks like it is the WHT/ORN & PPL wire. If it is original, that wire goes from the junction block and splits above the distributor into two yellow wires. One going to the starter solenoid and the other to the ign coil. I believe the WHT/ORN & PPL is a resistance wire used to limit the voltage to the original ign coils. Not good for your HEI as it will require a full 12 volt source. You could use a voltmeter or a test-light and see if you have voltage present with the key in the on position and crank position to help identify its use. Darrell __________________ Be wary of the light at the end of the tunnel....It might be a gorilla holding a flashlight! 71 Blazer, ex-4WD...Bought it that way 55 GMC 55 Belair 2dr HT 67 El Camino

03-02-2004, 11:33 AM	#13
danho Pesemistic Optimist Join Date: Dec 2002 Location: Prineville, Oregon Posts: 227	So the red wire does NOT need to be split in 2? Just relpace if with a new wire and run it to the HEI? And to replace it, do I splice it as close to the junction block as I can or do I need to feed a new wire through the firewall and replace the whole thing? Dan.

03-02-2004, 12:01 PM	#14
SS55 Registered User Join Date: Nov 2003 Location: San Diego, CA Posts: 62	You are correct, it does not need to be split. The cleanest solution would be disassemble the firewall plug and replace the wire and contact with a new wire going to your HEI. You can splice it close to the plug and achieve the same effect as that will replace the resistance wire and give you 12 volts to the HEI. Darrell __________________ Be wary of the light at the end of the tunnel....It might be a gorilla holding a flashlight! 71 Blazer, ex-4WD...Bought it that way 55 GMC 55 Belair 2dr HT 67 El Camino

03-02-2004, 03:53 PM	#15
lloyd k Registered User Join Date: Feb 2004 Location: columbus,ohio Posts: 201	i have a 472 cadillac in my 67,it has hei- replaced the resistor wire,put an a internially regullated altenator,did away with the external voltage regultor,i have all my factory guages hooked up except the amp guage.wounderng what wire coming out of the firewall should hook to what ?i think it is a brown wire from the schematics that i have ,not sure ? thanks much lloyd k __________________ 67 swb gmc,big block cadillac powered,400 turbo,2.73 ratio and disc brakes-basically a frankenstein of many parts-

03-02-2004, 04:12 PM	#16
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	ammeter wires? Not sure exactly what you're asking... __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.



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03-02-2004, 04:58 PM	#17
lloyd k Registered User Join Date: Feb 2004 Location: columbus,ohio Posts: 201	what wire comeing out of the firewall to power ampmeter guage ? thanks lloyd k __________________ 67 swb gmc,big block cadillac powered,400 turbo,2.73 ratio and disc brakes-basically a frankenstein of many parts-

03-02-2004, 07:32 PM	#18
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	LLoyd K There is a black and a black/w wires for ammeter with 4 amp fuses. see diagram. Attached Images __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

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