Quick question about 88-89 CK trucks

[quaddriver]

On the pilot wire coming off the battery is what appears to be #8 wire (black w/red stripe) with a #12 fuse link - does anyone know the melt current rating for this link? it is down to 2" long from the previous owner and I want to replace it with a circuit breaker. I have installed an ammeter inline using 2 #10 wires to it, 2 #10wires from it since I didnt have any #8 (but had a 500ft spool of #10) this is the perfect time for me to rip out the fuse link.

[gen0]

My best suggestion would be to take the reading of the ammeter during start-up (When the in-rush current will be at its highest point). Make sure you have every accessory turned on to get the highest current flow you will have. Also watch the meter while the truck is idling at max accesory use until it reaches a normal operating tempreture. Take the highest reading and multiply it by 1.25. Take that to next standard size breaker and you will be in good shape.

Also, the #8 wire is there for a reason. Instead of using a single #10 for the input and another for the output, place 2 identical lengths of the #10 in parallel with each other for both the positive and negative of the ammeter. The cross sectional area of the 2 #10's exceeds that of the #8 so the max amp rating will be higher. Make sure the #10's are identical in length.

Hope this helps

[quaddriver]

Originally Posted by gen0

My best suggestion would be to take the reading of the ammeter during start-up (When the in-rush current will be at its highest point). Make sure you have every accessory turned on to get the highest current flow you will have. Also watch the meter while the truck is idling at max accesory use until it reaches a normal operating tempreture. Take the highest reading and multiply it by 1.25. Take that to next standard size breaker and you will be in good shape.

Also, the #8 wire is there for a reason. Instead of using a single #10 for the input and another for the output, place 2 identical lengths of the #10 in parallel with each other for both the positive and negative of the ammeter. The cross sectional area of the 2 #10's exceeds that of the #8 so the max amp rating will be higher. Make sure the #10's are identical in length.

Hope this helps

thats what I did - 2 lengths of #10 wire to the batt side, then 2 lengths of #10 from the alt side back to the pilot wire, all 4 encased in 1/2" loom and routed around the engine compartment.

problem is with the ammeter test, is that the pilot circuit really never sources all the current in the truck, the #8 from the alt goes to a terminal on the solenoid as does the pilot wire, when running the alt basically runs the truck and excess current goes to the battery, or in times of need, defecit current comes from the battery. I tried Key on, Eng off with lights on, blower high and got mebbe 30A.

somewhere there has to be a chart that equates link gauge with max current.

[gen0]

ahh ok, I see what you're looking for.

Fusible links..the actual link rating is determined by the wire size of the circuit it is protecting.

In your specific case (An 8 awg wire for the circuit) the link itself will be made of #12 wire (4 sizes smaller than the wire used for the circuit)

the tricky part is that wire ampacities are rated for their insulation, not the current carrying capability of the wire itself.

Typically a #8 wire with insulation rated for use in a 105 degree C environment (Inside an engine compartment on a hot day with the vehicle running at normal operating tempreture) is right at 68 amps. The fusible link using the same satndards and being made of #12 wire is rated for 38 amps which is 125% of a 30 amp circuit protection rule listed by the 2002 NEC.

Here is a link to the chart http://www.bluesea.com/circuit.htm

Hope this answers your question.

[quaddriver]

thanks, thats about what I was looking for, it looks like 40-50 amp is what I need