2009 Sunsport 24V starter fuse keeps blowing

[bshelton]

20A starter fuse on Indmar 340 Assault (5.7L) engine block keeps blowing, engine won't crank. Boat only has 75 hours on it. Removed starter and tested, operates normally. Solenoid draws 37A. Checked with a known good starter and it also draws nearly 40A on the solenoid side. No damage to engine wiring harness visible. Starter relay on engine clicks when key turned to start. Any assistance gratefully appreciated!

Barry

[CJD]

I assume the 37 amps is free spinning at the large post?

The amperage you are interested in, however, is the small solenoid post, not the large post. Remove this wire and test the resistance to ground at the wire. It should be infinite. Then see how much amperage is used to activate the solenoid through the small post on the solenoid. It must be below 20 amps.

You may have a second relay between the switch and starter that could be shorted.

[bshelton]

I assume the 37 amps is free spinning at the large post?

The amperage you are interested in, however, is the small solenoid post, not the large post. Remove this wire and test the resistance to ground at the wire. It should be infinite. Then see how much amperage is used to activate the solenoid through the small post on the solenoid. It must be below 20 amps.

You may have a second relay between the switch and starter that could be shorted.

Actually, that's 37 amps on the small post, just to actuate the solenoid. Measured using a DC clamp ammeter, with nothing connected to the large post on the starter. The starter motor would draw much more than 40 amps, even free spinning. Also, the resistance between the large post and ground indeed should be infinite, but the resistance between the solenoid terminal and ground is about 0.5 ohms, and about 0.3 ohms resistance for the starter motor.

There is a starter relay, and because neither Supra nor Indmar have favored us with an electrical schematic, it's not clear to me whether the coil side of the relay is what's protected by the 20 amp starter fuse. If anyone has the engine schematic for a 2009 340 Assault (5.7L), I'd appreciate it.

[CJD]

Good luck...I have talked to Skiers Choice and Indmar, and they all start acting like I am not speaking english when I ask about a wiring diagram.

The bottom line is this...a 20 amp fuse will blow every time if it is seeing 37 amps of draw. But, there very well may be a relay between the starter and the key switch. The easiest way to check without a diagram is to disconnect the small post from the starter, turn the key and see if you hear a clicking of a relay on the boat. In a well designed system it will belocated rather close to the starter...so somewhere in the engine bay.

If there is no relay, then perhaps the 20 amp fuse was supposed to be a 40 amp all along...