No start issue

[Ifyasquintitsmint]

I've had 3 subsequent no start issues that I've been fixing and I'm at my wits end trying to figure out what's going on with my truck.

First no start issue was my fusible link blew, checked everything else swapped the battery because it was 8 years old and not holding a charge.

Second my ignition module went out, took a bit to swap out but worked and just drove the truck 2 hours yesterday.

Today no start again. Battery has 13.5V, no power to the firewall, I think the fusible link blew.

Would it be a terrible idea to swap the fusible link w a inline fuse until I figure out what's causing my issues?

I've wired in a subwoofer to the battery and power locks to the firewall, but that has been the only modifications I've done.

This is all within this month so any help is appreciated. Getting tired of electrical work

EDIT: I've also still had taillight issues with a bulb staying on after the trucks turned off.

 

[Tank6x2]

I’d say You have a short to ground either through your headlight switch, depending on your year dash - easiest enough - I think 85-87 in the column pain in the arse but unlikely as it would be more Than one tail light, check around the trailer plug in for the constant source voltage maybe a crossed wire in your previously installed fusible link that’s not supposed to be there, but only one taillight makes me think a short somewhere in the harness… any green monster in your battery cables - when’s the last time starter was replaced - voltage drop across the starter, battery cables, check your body ground wire