Does the Ignition (40A) fuse pop as soon as you put it in or just when you turn the key?
Only when I turn the key to start. That's why I think it's the starter "trigger" wire causing the fuse to blow. I've got excellent frame, engine block and body grounds
Did the fuse blowing start before or after you worked on it?
Hello 98tahoe4dr,
The above Q & A is very good, and really tightens up the problem description, for given the fanout
from this 40A fuse the circuit choices I initially saw in the wiring diagrams were:
*
Hot At All Times
*
Hot in Accessory only
*
Hot in Run and Start
* Hot in Start Only
So that's solid troubleshooting progress. Your problem description allows us to ignore a whole lot of real estate in the
wiring harness. And since you are able to force the error at will, further troubleshooting will be clear & unambiguous.
But as you have mentioned, blowing 40A fuses every single time you want to test the circuit is a potential budget buster.
And I face a similar issue in one of my other hobbies. (One of the things I do for pleasure is repair/optimize old high-power audio amps.)
Of course, after doing invasive surgery on an amp with 36 250W TO-3 output devices, just plugging it in to full line voltage
and flipping the switch really runs the risk of living through a Wile E. Coyote moment. :0)
Therefore, one of the first things I invested in was a large previously-enjoyed Variac (driven by a little old lady on Sundays while working
on the church PA) so that I can test/verify my handiwork by powering up the patient slowly and with great care. (See attached.)
Q: What does this have to do with you?
A: Others have already suggested this, but I wanted to highlight it just in case you missed it. Temporarily substitute a
single headlight in place of the 40A fuse. This will throttle/limit the max amperage drawn by the circuit (even with a dead short somewhere)
to ~5 amps and also giving you a go/no-go visual indication whether or not you have successfully cleared the dead short condition:
Best of all, instead of the fuselike one-time use scenario, the headlight will last hundreds or even thousands of hours while performing
this current-limiter/virtual fuse function, affording the luxury of time to savor the hunt for the dead short:
You must be registered for see images attach
In other words, you are going to disconnect the (smaller) purple cranking wire connected to your starter solenoid,
so in theory with this load removed from a healthy circuit you should draw no appreciable amps/power from this 12v
path when you turn the key to the START position.
IF this circuit
still has a short, then the headlamp will light up brightly. You will focus on this circuit until you can
crank the key to the START position and the head lamp remains out. IF your starter solenoid is not a dead short
itself, then you should have regained control over this circuit.
Does this make sense? This all works because the current flow in a series circuit is the same across all components.
So instead of testing with max current until the fuse opens, we are now testing the entire circuit with 5 amps worth
of current. (Should be fine, just don't leave the circuit under test left powered up while unattended.)
I'm going to go poke around the 'Hot in Start only' circuit and see if we can dig up some additional info
for your troubleshooting session.
Don't give up. And when you find the root cause of the dead short make sure and take some clear
photos for others to learn from.
Best of luck in tracking this down --