Ok guys, need some electrical help! (ignition related)

['99 Python]

Big thanks in advance for all who help! '99 Sport/Air with 502 Python. Took the kids out skiing and swimming the other day and everything worked fine. Went to start boat and it cranked, but did not fire. On the 3 fuse pigtail that's hanging from the relay/starter solenoid box, it had blown the 15 amp fuse on the far left. It goes 15/10/15 on the fuse block. I replaced the fuse, but as soon as I turn the key to on, to engage the fuel pumps before start up, the fuse blows! I have gone around and checked all the grounds, including the battery itself, but no dice. I have already replaced both relays, so they are brand new. Can somebody please give me an idea of where to start, and/or what that fuse specifically controls, so that I can get this worked out? There have been no modifications or anything that would have changed anything. It worked, and then it didn't...all in a three hour span. I have used the search function, but most of the problems are related to GT-40's, so that's not helping much. Thanks a ton guys! I need to get back out there ASAP!

['99 Python]

Ok, update! I've determined that it is the low pressure fuel pump, because when I unplugged it, the fuse didn't blow, and the boat fired right up. Now, Summit Racing carries the replacement Carter pump, but I have no idea what psi the low pump is rated for. They offer a 72 GPH/6 psi pump and a 72 GPH/8 psi pump for the exact same price. Which would be the one I need? Keep in mind, this is the Python 502 BB. Also, I've covered the boat for the evening, and didn't check what size fitting it is, 1/4 or 3/8. Obviously, I will check in the a.m., but just to make sure they have them in stock, does anybody know the correct psi and inlet/outlet fitting on the pump? Thanks guys!

[core-rider]

I would say it is definitely the 3/8" fittings. 1/4" could never move the volume of fuel the engine would need. As far as pressure I don't see any real reason you couldn't run 8psi. The LP pump only lifts fuel to the FCC and then the HP pump raises the pressure to around 35-40psi. Even if you do run 2psi more on the LP side it shouldn't matter.

[DanielC]

I would not recommend using the summit pump. Marine fuel pumps are sealed so they cannot leak fuel or even fuel vapors.
If an automotive fuel pump leaks some vapor, the vapor just falls out of the engine compartment, and dissipates. In a boat, the vapors collect in the bilge, waiting for a spark, so they can explode, and maybe even start a fire.

['99 Python]

Wouldn't even think of using an automotive pump. I'm talkin' marine. Summit carries all the sealed, Carter marine pumps. I live 15 minutes from there, and they're open on Sunday.

[bchesley]

If they are that close then remove the old and take it with you. I bet there is a part number on the old pump they can look up to make sure you are getting the right one.

['99 Python]

That's exactly what I did this morning. Carter #GP4389 in case anyone needs to know. 12V, 72GPH, 6psi, 1/4 in. NPT, sealed marine replacement. $123.95 out the door. Just tied up the loose ends and took it for a blast around the lake. Flawless! Thanks guys! I'm headed out!

[core-rider]

WOW! Very surprised it was 1/4" fuel lines.