Starter/Solenoid fried wires on header

[JACKED_JIMMY_79]

So...quick summary on my first real grown up post here:
1979 GMC Jimmy 400ci with HEI
Last weekend I was doing some off roading steep elevation changes etc. Every few weeks I get out there. Anyway, 2 wires going away from solenoid were roasted against headers...dead. I did what I needed to do to get it started and back home. Sacrificed the insides of an extension cord and twisted them together and wrapped in electrical tape. Was in sand and dark so I did the best I could.

Here's my question before I replace the 2 wires:

• Q1 2 wires go from the solenoid to...? Should I splice or run new wires the whole way (I think I know the answer but have not looked at it yet).
• Q2 Was thinking 10-12awg. What gauge wire should I use?
• Q3 Recommendations on prevention?

Thanks for any insights on doing this and/or answering questions.

 

[trukman1]

Not much help but earlier model V8's used to have a metal tube that protected the wires. It bolted to the starter and the rear of engine (if I remember correctly.) Somebody on here probably has one if you post in the WTB section.
Sorry, don't have pics.
As for wire size, just match to the existing wires.
You can splice but I'd only do so by soldering then using the shrink tubing with the adhesive and I'd apply some dielectric grease to the bare wire before covering with shrink tube. Be sure to slip the shrink tube on before soldering. I know, just common sense but you'd be surprised how often that gets overlooked...gives you that...uuuggghhh feeling! I know!

 

[Fordum]

Word of warning: Not sure which wires we are talking about, but a couple of those in that area are fusible links, not just general wires.
Fusible links are slightly special. The metal in them is nothing special, just regular copper. But it is a special size. And the originals are usually covered with a flameproof insulation.
The gauge of the wire is chosen to melt and break the circuit before the wire they feed does. This lets any smoke or heat to occur out in the open away from anything flammable.

If I remember right, they are usually two wire gauges smaller than the wire they feed. You can buy replacement links, or a roll of the right size wire. Nowadays most modern cars use actual fuses. Back in the days when these trucks were being built, automotive type fuses in that high a current range were not very common if they even existed. Almost all modern vehicles have some now. I think several folk here have upgraded their trucks to use high current fuses instead of the links. Hopefully someone will chime in who had done that.

Some time ago I linked to a website that sold fuse link material and gave current ratings for the various sizes of wire so that the proper size replacement fuse could be chosen. Not sure where it is now, but I will scout around.

 

[Fordum]

Found one link, pretty sure there was another, but don't see it now.
http://www.madelectrical.com/catalog/fusible-link.shtml
Not sure if this outfit is still in business, website has not been updated for a long time. And it looks like I was wrong, its 4 wire gauges smaller. Most of the automotive stores sell fusible link replacements, you just need to know what size you need.

Also, there are some discussions about the idea of replacing fusible links with Maxi-fuses. There is a lot more to fuses than current and voltage. Different fuses break the circuit at different rates under the same conditions, and Maxi-fuses don't have the same performance curve as a fusible link.
I have not seen the numbers, but I suspect that the Maxi-fuse would blow faster than the link. But not sure.

 

[Kain]

if you undo the connection at the starter you should be able to pull that section of the harnes up around the back of the motor and work better with it and see what its doing( its what i did when mine did same thing)

 

[6872xtc]

One wire should be a power feed with a fusible link like @Fordum described. The other should be the wire to engage the starter.
As far as the metal tube that the factory used on the wires, I have found a couple of trucks with the insulation on the wires worn and in poor shape inside the tube, so it isn't a sure cure, but it helps. I position the wires to run over the top of the starter solenoid which helps keep them away from the header as best as I can. Maybe try some of the heat reflective tape that is on the market, just wrap the wires from the starter to just past the flywheel area.

 

[Wes Harden]

yes the tube mentioned needs insulation around loom thru it. I am changing my wiring to use a 2nd solenoid. Since you are running headers I think you should consider this option. This allows you to move the small wires away from the hot tubes. hopefully my diagram will help and not confuse. Dia on left is original wiring, right is 2nd solenoid option.

 

[Kain]

This ^^ is a good idea my buddy in vegas wanted me to do this when i had headers

 

[diesel4me]

That metal conduit tube only helps the wires insulation to dry out and crack,then allow a short to ground happen--it was not GM's smartest idea..
What I've done on many of my GM trucks,was to wire them up the way GM had done it up until 1972 or so--the wires with the fusible links that go on the starter solenoid's post where the positive battery cable goes,I moved those wire(s) to the battery terminal itself,leaving the fusible links intact--you may have to lengthen the wires to do this--I used 10 gauge wire if that had to be done....that way.you can route the wires up along the inner fender,far away from the exhaust manifold..

Some trucks had only one red wire with a fusible link at the solenoid,others had two of them..

When you do this,the only wires going to the solenoid will be the positive battery cable,and the purple "crank" wire that makes the starter crank when you turn the key to start--so there is much less to face a chance of being scorched or shorting out..
I put that split plastic wire loom over the battery cable and route it as far away from the exhaust manifold as possible..

I "think" the fusible links they used were either 14 or 16 gauge--it's been awhile since I sold any..

 

[JACKED_JIMMY_79]

First of all thanks for the info it has been helpful! I rewired everything like the left side of Wes Harden's illustration (probably factory). When I ran the new wires thru that tube, I noticed that the tube had come off and may have contributed to the excessive movement - hard to confirm without seeing with the original wires. The bolt was still there on the tube (very had to reach because it was on the backside) but I reattached it. To aid in heat control I wrapped all wires with the shrink heat wrap all the way into the tube and ran as straight as possible. Tonight I am going to wrap a few inches of each header in that section with extra motorcycle exhaust fiberglass wrap I have laying around. Adding the wrap may not do a lot other than make feel better! Again, thank you for the insights. Hitting the trail tomorrow for a night run!