Bilge Fire Today - thoughts on cause?
06-21-2025 | 06:26 PM
#41
Registered
Joined: Feb 2013
Posts: 1,459
Likes: 391
The orange wire connecting the alt output to the "battery cable" at the starter solenoid should have some sort of circuit protection (fuse/breaker/fuseable link) at the starter solenoid end. Hard to find a good schematic, but of the ones I found, some show a 90A fuse (looks like a 1" cube) and others just show being connected directly.
The wire size should be able to withstand the alternators full output (35A, 55A, etc) so circuit protection at the alternator end of the orange wire is not needed. (This is why the wire size needs to be increased if installing a larger capacity alternator)
If the alternator shorts to ground internally (or orange wire gets grounded somehow) and there's no circuit protection at the starter solenoid connection of the orange wire, the batt can flow hundreds of amps thru that wire. That's my WAG as to what happened.
IMHO, If the ops new harness doesn't include a 90A cube type fuse, he should seriously consider installing one, even if it's not shown on the applicable schematic.
The wire size should be able to withstand the alternators full output (35A, 55A, etc) so circuit protection at the alternator end of the orange wire is not needed. (This is why the wire size needs to be increased if installing a larger capacity alternator)
If the alternator shorts to ground internally (or orange wire gets grounded somehow) and there's no circuit protection at the starter solenoid connection of the orange wire, the batt can flow hundreds of amps thru that wire. That's my WAG as to what happened.
IMHO, If the ops new harness doesn't include a 90A cube type fuse, he should seriously consider installing one, even if it's not shown on the applicable schematic.
Last edited by zz28zz; 06-21-2025 at 07:27 PM.
06-22-2025 | 07:38 AM
#42
Registered
Joined: Mar 2020
Posts: 846
Likes: 507
most times a fusible link on the alternator is at the battery or starter post. problem with this is if it shorts between the link and alternator (wire rubs thru on the engine mount or such) the alternator is the source of power so it can just go to full output and the link never sees that load. fusible links work great when the short is on the opposite side of the power source (battery) but the alternator is also a power source and if it is spinning then it is powering. I guess if the link is on the alternator end of the wire it would work but that is not how most are wired.
The orange wire connecting the alt output to the "battery cable" at the starter solenoid should have some sort of circuit protection (fuse/breaker/fuseable link) at the starter solenoid end. Hard to find a good schematic, but of the ones I found, some show a 90A fuse (looks like a 1" cube) and others just show being connected directly.
The wire size should be able to withstand the alternators full output (35A, 55A, etc) so circuit protection at the alternator end of the orange wire is not needed. (This is why the wire size needs to be increased if installing a larger capacity alternator)
If the alternator shorts to ground internally (or orange wire gets grounded somehow) and there's no circuit protection at the starter solenoid connection of the orange wire, the batt can flow hundreds of amps thru that wire. That's my WAG as to what happened.
IMHO, If the ops new harness doesn't include a 90A cube type fuse, he should seriously consider installing one, even if it's not shown on the applicable schematic.
The wire size should be able to withstand the alternators full output (35A, 55A, etc) so circuit protection at the alternator end of the orange wire is not needed. (This is why the wire size needs to be increased if installing a larger capacity alternator)
If the alternator shorts to ground internally (or orange wire gets grounded somehow) and there's no circuit protection at the starter solenoid connection of the orange wire, the batt can flow hundreds of amps thru that wire. That's my WAG as to what happened.
IMHO, If the ops new harness doesn't include a 90A cube type fuse, he should seriously consider installing one, even if it's not shown on the applicable schematic.
https://www.ebay.com/itm/13543601365...55-0&loc=82786
Seafordguy, did you notice if you had that fuse in place?
On a side note, I looked into this for my high output alt and it's showing installing a fuse between the alt output wire and less than 12" from the battery.
06-22-2025 | 09:18 AM
#43
Thread Starter
Gold Member
Joined: Jun 2006
Posts: 5,120
Likes: 965
From: Seaford, VA
You guys are correct. I do remember seeing that square block on the starter relay post.
https://www.ebay.com/itm/13543601365...55-0&loc=82786
Seafordguy, did you notice if you had that fuse in place?
On a side note, I looked into this for my high output alt and it's showing installing a fuse between the alt output wire and less than 12" from the battery.
https://www.ebay.com/itm/13543601365...55-0&loc=82786
Seafordguy, did you notice if you had that fuse in place?
On a side note, I looked into this for my high output alt and it's showing installing a fuse between the alt output wire and less than 12" from the battery.
can you confirm instal? funny the diagram that Hardin sends with that harness does not show this fuse.
im wiring according this diagram, the only thing im apparently not using is the “12v sense wire” coming from the alternator and the purple “Excite wire to alt” which is consistent with the other motor- those are taped off.
https://www.hardin-marine.com/instru.../620-08904.pdf
Looking closer though at that Diagram, I’m not sure how that provides more protection given it is after the 50AMP breaker which I would assume would trip first anyways since it’s the most direct route from ALT, through Batt Post up through breaker unless I”m missing something?
Last edited by seafordguy; 06-22-2025 at 09:43 AM.
06-22-2025 | 08:35 PM
#46
Registered
Joined: Mar 2020
Posts: 846
Likes: 507
definitely did not have that. I’ll order two right now.
can you confirm instal? funny the diagram that Hardin sends with that harness does not show this fuse.
im wiring according this diagram, the only thing im apparently not using is the “12v sense wire” coming from the alternator and the purple “Excite wire to alt” which is consistent with the other motor- those are taped off.
https://www.hardin-marine.com/instru.../620-08904.pdf
Looking closer though at that Diagram, I’m not sure how that provides more protection given it is after the 50AMP breaker which I would assume would trip first anyways since it’s the most direct route from ALT, through Batt Post up through breaker unless I”m missing something?
can you confirm instal? funny the diagram that Hardin sends with that harness does not show this fuse.
im wiring according this diagram, the only thing im apparently not using is the “12v sense wire” coming from the alternator and the purple “Excite wire to alt” which is consistent with the other motor- those are taped off.
https://www.hardin-marine.com/instru.../620-08904.pdf
Looking closer though at that Diagram, I’m not sure how that provides more protection given it is after the 50AMP breaker which I would assume would trip first anyways since it’s the most direct route from ALT, through Batt Post up through breaker unless I”m missing something?
I looked up my gen VI HP 500 (carb) engine and it does NOT show the 90A fuse on any of the parts diagrams.
06-22-2025 | 09:58 PM
#47
Thread Starter
Gold Member
Joined: Jun 2006
Posts: 5,120
Likes: 965
From: Seaford, VA
07-03-2025 | 04:00 PM
#50
Thread Starter
Gold Member
Joined: Jun 2006
Posts: 5,120
Likes: 965
From: Seaford, VA
I guess it might have been a blessing in disguise.
Installing the 90A fuse on the starter on the motor that didn’t catch on fire and I noticed the starter was loose. Turns out the bolts that clock the starter had backed out.
Undescribably unpleasant getting that thing off the port engine with them in the boat. If I read the technical pages right, those things are 50-inch pounds - ripe for someone to strip them out, which one was. I had to put a nut on the backside and put locktite on both.
on the backside and I put them both back in with Blue Locktite.
Installing the 90A fuse on the starter on the motor that didn’t catch on fire and I noticed the starter was loose. Turns out the bolts that clock the starter had backed out.
Undescribably unpleasant getting that thing off the port engine with them in the boat. If I read the technical pages right, those things are 50-inch pounds - ripe for someone to strip them out, which one was. I had to put a nut on the backside and put locktite on both.
on the backside and I put them both back in with Blue Locktite.
