Fusible links and wire size for 87 chevy R20 w/t 350tbi

[87 Wrangler]

Hey guys, i am looking for any info on wire size from the starter solenoid to the junction block located on the firewall. It looks like #8 or #10 but not too sure. The fusible link is melted down by the starter (heat from the manifold and old salt corrosion), so im looking at running a new wire up top from the battery, around the fender/ firewall and over to the block. Problem is fiquring out wire size and fusible link size for this. It only feeds 2 wires on the block, one for the dash i think, second for my brake controller.
The wiring diagrams are confusing for this year, 87- some carb some not... My 86 parts truck has multiple wires coming from the same block... so im confused.
Any info would be great

[bd]

Fusible link is an engineered alloy wire jacketed in high temperature rubber insulation.  The rule regarding fusible link selection is fairly standard.  Protect any given wire gauge using a 6" length of fusible link that is four wire gauges numerically higher than the wire being protected.  Install the link between the power source and the wire run. 

So, 10-gauge wire is protected by a 6" length of 14-gauge fusible link installed between the wire and the battery; 12-gauge wire is protected by a 6" length of 16-gauge fusible link; 14-gauge wire is protected by 18-gauge fusible link; 8-gauge wire is protected by 12-gauge fusible link, and so on. 

The 1987 wiring manual lists wire sizes by the cross-sectional area of the wire in (mm)² instead of American Wire Gauge (AWG).  Fortunately, metric and American wire sizes have a direct correlation that is shown in a table near the front of the wiring manual.  The red B+ lead to which I think you refer that comes off the starter is 3.0 (mm)² (or 12 AWG) and is protected by a 1.0 (mm)² (or 16 AWG) fusible link.  It won't hurt to increase the main wire size to the junction block if you wish, but DO NOT use a smaller wire.  Size the fusible link accordingly.  To replace a fusible link, refer to How to make a Fusible Link.

[87 Wrangler]

Great thanks bd! The old fusible link looks to be approx 6" long as you said, as for size il match it up close as i can. Are these fusible links colour coded? It goes small orange wire to bigger red supply wire. Not sure if that helps determining my size.
Thanks

[87 Wrangler]

An update to the wire size, I stopped at Napa this morning and got a piece of #8 to compare the size. It is very close, if a tiny bit smaller than the original wire. I'm thinking that's it (insulation is thinner now maybe?) Just for fun I popped open the hood on my 86 carb truck and the original wire feeding the block on it is significantly smaller than the #8, like 10 or 12 probably and is feeding 4 wires. (On the TBI it only feeds 2 wires) It also has a 37amp alternator on it vs my 78amp on the TBI. I don't really understand why the difference in wire sizes between the 2 trucks.

[bd]

Are you certain the "#8" is the original wire?  That sounds suspicious, but then I haven't had time to study the wiring diagram.  Factory feeds should be 12- or 10-gauge.

[87 Wrangler]

I'm sure it's factory, my father ordered the truck new in 87. Niether of us have changed any electrical on it, and at the starter end the black cylinder thing is still on the wire to identify the Link. I had him look at it the other day to verify. I do agree with you the size seems way overkill. Doesn't seem to be any explanation for it. Here is chunk of new #8 beside the original. It is slightly smaller than original, I'm thinking it's #8... So if that is the case i would need a 6" long #12 fusible link attached to it correct? Thanks

[bd]

You can't judge wire sizes accurately by comparing the OD's of the insulation.  Strip 1/4" - 1/2" of insulation off the ends of the wires and compare the overall diameters of the conductors.  If you have 8-gauge from the factory, it is a deviation from the factory schematics and possibly a mid-year production change.  (My '87 was built with 12-gauge feeds).

Nonetheless, for what you are doing 8-gauge wire protected by 12-gauge link, or 6-gauge wire protected by 10-gauge link, will work just fine for you as the main B+ feed to the firewall junction block, as long as the remaining wires that connect to that block are individually protected by their own fusible links or fuses.  Be sure to install the fusible link between the wire and the battery.  I recommend that you use GXL or SXL rated wire for the 8-/6-gauge run and house it in convoluted or asphalt loom.  I also recommend crimping, soldering and heat shrinking all wire terminations and splices.

[87 Wrangler]

Thanks for the info! I just picked up a 3.0 mm fuse link from my mechanic. It says it is a 12 so should be good for my #8 wire. Gonna do just as you said and try to get it hooked up this weekend. I appreciate the info guys il let you know how I make out.

[87 Wrangler]

Well I stayed out late last night and hooked up that new #8 wire and link. Put it in some plastic loom and kept it clean looking to try and make it look factory. Its a wonder how that other wire being almost completly broke and corroded still worked. Thanks for all the info fellas!!

[bd]

Glad to help!