Starter Wiring A Mess! Need Info on Proper Connections

A bit long but I'm trying to relay as much info as possible.

So, while trying to resolve my RobbMC hot-start issues, I discovered a host of other issues. I've tried comparing to the wiring harness on my 71 350 without an engine and it is different, as detailed below.

1) There is only ONE wire on the main starter lug powering the whole car and it was NOT a fusible link.
2) The one wire from the start main lug went to the back of the alternator.
3) Alt has another wire that went to what looks like a factory junction crimp where another wire hooked onto it.
4) 71 has a factory crimp where two wires run together and joined before splitting again.
5) Headlight wire was connected to the main wire just before the factory crimp.
6) Solenoid Start wire was cut/spliced with, looks like 14ga instead of 12ga on the 71, I could be wrong.

So far, I've done the following:
1) Connected a new 12ga wire to the solenoid start terminal.
2) Have 2 fusible links, 14ga for 10ga and 16ga for 12ga connections along with stepdown butt connectors.
3) Headlight wire seems pretty straight forward, disconnect from main power and connect to 16ga fusible link.
4) Remaining wire from main starter lug up to top of the engine but not connected yet, this is the question part.

Where does the main power from the starter lug normally go?

Should/could I connect it to the same lug on the back of the alternator or do I need to get it into the bundle along the valve cover with crimp? Electrically, it will back feed power since it was like that before but also running the headlights. If I put it back that way, the headlights will be on their own circuit/fusible link.

Does this make sense? I haven't dug into the manual yet.

 

I hate to be "that guy", but gonna take one for the team.

RTFM.

You have to know what you have and don't have, and that means you have to look at the manual and sort the wiring out from what is installed.

What I do and would do in your case is pull the engine and front harnesses completely out of the car and separate them, then start at the firewall connector and inventory every wire and connector.

Then considering the condition and the "correctness", of the harness, and what it would take, parts and labor to make it correct and properly functional, vs purchasing the best correct harness, or have someone make you one.

I build or repair all my wiring, with the exception of the front and engine harness for my '64 Skylark as I was going to "GS harnesses" with several mods. Due to the time and all I was doing on the resto, swapping everything driveline and suspension, I had Loren Alexander (member "la 65 gs" and owner of 65GS.com) build my harnesses.

Not getting the wiring correct and proper will result in a lot of frustration with failures and intermittent problems, safety on the road in rain, at night, and most importantly, risk of fire, and a car fire is a bad thing, especially if it is garaged.

There is no end to people who will counter what I am saying and all manner of them that "have just cut and crimped and it works just fine". Not to be harsh, but those folk's advice is not what you need.

I will gladly help identify connectors, terminals and such, as well as advise along the way, no matter if you elect to do it all yourself, purchase ready made harness, or have someone do all/most of the work.

And a bunch of folks hear can help.

Wiring is not complicated, it's just complex, sort of forest and trees, You gotta get up close and look at each one, and "learn" the forest along the way. And it takes some time.

 

I've got the book. I didn't have it in the garage with me. It is in my home office and I don't like to use it with grimy hands. I have the 71 harness to compare it to but they are different enough I don't think it will help much.

Yep, bought those and the smaller is for the headlights. I had none before today. This has likely been like this for 40 years from when it had a BBC in it. I found the oil pressure wire looped around in a bundle since it didn't need to go all the way to the front for a BBC. Straightened that out.

 

If your service manual isn't torn and greasy, you aren't using it enough.

 

I'll take a pic of the 71 harness with the two wires crimped to two wires that isn't present in the 70 harness and I don't see anything even close to it in the diagram posted.

 

Get one of Todd's poster diagrams, take it to UPS/Kinkos and get it laminated. Keep it in the garage!

 

As Bill mentioned I do have Poster Size Wiring Diagrams. They're the Factory GM Chassis Manual Diagram but big enough to actually read! These are not the Bootleg Diagrams that are on the market. These are Factory GM!

I also have new Engine Harnesses in stock and priced below retail if the one you have gets you to that point!


Here's some Links if you want to check into it further. . . .

Engine Harnesses (1970) > https://www.stage1restoration.com/product/engine-harness-1970/

Poster Size Wiring Diagrams > https://www.stage1restoration.com/product/1970-1972-wiring-diagram-poster/

 

Here's the splice on my 71 and the 70 car has similar but only crimped two wires heading out of the one from the back of the harness. I don't see anything that represents this on the wiring diagram.

 

It is these wires. (relevant to your image) The crimp is the area pointed to by the green arrow.

Can you show pics of the connectors on the 70, for the wires from that splice?

 

Ah, I thought that was a jump-over not a junction. I'm not used to that type of drawing with a background in networking.

 

Yep, going to have to figure out which wire is missing from the bundle. One coming from the junction is missing toward the firewall. A little sleuthing to see where the one wire goes and get the other one connected.

What can I use to crimp those wires together? What do you call that?

 

OK, I understand where it all goes now that I know that little dark spot on the diagram is a junction and not something else. The wire from the starter main lug was going to the alternator and a second wire off the alternator went to the point where 3 wires converged. It was using the alternator lug as a junction block. I just need to pull the wire to the junction to make it 4 wires and only feed one back to the alternator.

Electrically, it is more or less the same to my untrained eye. Maybe a little more resistance from running on a single 10ga wire for a foot to reach the factory junction. My 70 harness looks, for all purposes like it was an original 3-wire crimp.

It's a good thing I bought plenty of electrical tape and convoluted wire loom.

 

What you describe will work, but it negates the fuse link on that circuit.

If the link fails, power still flows from the battery, to the alternator to the junction, instead of not flowing as no power would flow to the wires 2,3,4 if the wiring is per the diagram.

So, a short/overload that takes out the fuse link, will then overload the rest of the circuit.

The link(s) are to supply from the starter lug (from battery) then pass through the 2 fuse links to protect the wiring to the paths 2,3,4 as well as to the front harnesses and the fuse block busses to the rest of the car.

By running the wire from the alternator to the starter solenoid lug, and the other wire to the junction, even with the fuse links, that wire will effectively bypass (at least one) link(s) as the fuse link(s) will be higher resistant path. There is logic to the wiring as designed, and often, these older cars have had the wiring compromised buy previous owners, and as you stated, with engine swap.



The four wires you need (per the diagram/correct harnesses)

1. Starter Solenoid (large lug with fuse link ) to the junction.
2. Alternator "Battery" lug to junction.
3. Voltage Regulator terminal for "current sensing" of alternator to junction.
4. 12v supply to firewall connector (power to fuse block buss) to junction.

In effect, the battery supplies current from the positive post to the starter lug (cable see below), from the lug to the junction (#1) and then branches to 2,3,4. (and current from the alternator flows back to charge the battery controlled by the regulator)

 

Use a butt connector. Similar to what's there. Slip heat shrink over one pair of wires big enough to cover everything then strip the insulation off the connector if it has any, crimp it over the wires, then soldier it. Slip the heat shrink in place and shrink it. You can use two layers if you want!

 

Here's the mess in the 70. I need go back a bit and clean up that nastiness there. The stray wire, bottom left is the headlight wire. The bare spot on the top of the two left junction wires is where the headlights were connected. It will be all better tomorrow.

I ordered some 6ga butt connectors to get the 2x10ga in each side of the new part that is going in. I couldn't find anything locally that would crimp them together.