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Hi all, I am working on a 75 CB400F and am running into an incredibly frustrating issue. Every time I turn the ignition switch to on, the main fuse blows. Measured amps on the fuse box main circuit (where the 15 amp fuse should be) goes from 0 (off) to ~41 very briefly when turned on, then it quickly goes down to 14. (Assuming I'm using my multimeter correctly...)

When we got the bike, it was running (not great tho, it was very lean because it was built and tuned at an altitude 5,000ft higher than me. Engine struggled to get past 7k rpm) and we rode it probably around 50 miles. It died on the highway, which is when the fuse blowing issue started.

The bike is nearly fully restored and rebuilt, plus the engine was bored and honed with cylinders 50 over installed. New wiring harness too. It is a very nice, clean bike.

I upgraded the ignition timing systen and ignition coils with the Dynatek system and replaced the oem rectifier and regulator with a new, modern combo unit. I also installed a brand new ignition switch, diode, fuse box, checked and cleaned all leads (except for the wires in the main loom. I haven't cut into it yet since it's brand new), checked the grounds, the battery is brand new, & installed a custom 6sigma jet kit.

I believe the only OEM electronic component left on the bike is the starter solenoid (and maybe the starter?). I ordered one as I suspect that might be the culprit.
I hoped upgrading the points system to an electronic system, installing new coils, making new spark plug wires, and replacing the old corroded ignition switch (that had brake fluid in it) would solve the issue.

The weird thing is, at first it did. After we finished installing everything, the bike turned on and it started without blowing a fuse. We ran it for a bit at idle, then it stalled while I was trying to tune the carbs and playing with the choke. So I turned it off and when I turned the key back to on, the main fuse blew again...

Can a bad starter solinoid cause the main fuse to blow?
Do these bikes have common issues that cause the main fuse to blow?
Any reccomdations if the starter solenoid isn't the cause of the short?
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