Blown Mega Fuse

[cldonley]

I'm just a few steps away from having my rig on the road. Completed the Cherokee wiper upgrade and went to start him up and lost all power as the starter engaged and then missed a beat. The starter sounded like it does when the timing is too far advanced. Inspected all the wiring and fuses, no issues noted. Battery was at 13.3 volts. Found the mega fuse blown. Bypassed the fuse and found all systems working fine including the starter solenoid, didn't risk trying to engage the starter. Pulled the starter and took it to O'Reilly's for testing where it passed, but that is suspect since it is not tested under load. It spun fast but was pretty noisy/rattling. The starter was on the original 302, so it's pretty old and was sounding a little wimpy before this happened. Considering ordering a gear reduction starter and just going for it. Any advice? And which starter is everyone using? I was about to order the WH offering.

1969 with 351W, RAT, serpentine with 3g, painless harness.

Thanks!

 

[904Bronco]

I have used the PM starter for a 92 F150 truck with 5.0 and manual trans... with Explorer 5.0's and manual transmissions. But it is good to know flywheel size/tooth count.
I doubt that there is anything American made anymore, so you are probably stuck with off-shore. Then it just becomes a price point and warranty review. I guess some places have a budget level and then a higher level = more $$.
I have been a Napa guy for more years than I should count, and well they carry more Off-shore stuff than I care for.

The folks at WH's and Tom's have treated me well over the years, even if I had a warranty issue (rare), so I would say stay with the folks that support us. If there is an immediate need, and you can find it locally, then it gets back to availability, price, warranty...

 

[cldonley]

I have used the PM starter for a 92 F150 truck with 5.0 and manual trans... with Explorer 5.0's and manual transmissions. But it is good to know flywheel size/tooth count.
I doubt that there is anything American made anymore, so you are probably stuck with off-shore. Then it just becomes a price point and warranty review. I guess some places have a budget level and then a higher level = more $$.
I have been a Napa guy for more years than I should count, and well they carry more Off-shore stuff than I care for.

The folks at WH's and Tom's have treated me well over the years, even if I had a warranty issue (rare), so I would say stay with the folks that support us. If there is an immediate need, and you can find it locally, then it gets back to availability, price, warranty...

I was recently disappointed by an offshore part from NAPA. WH actually has a cheaper option than the local part store-even after shipping. So I'll go with WH. I've never been disappointed by them.

 

[73azbronco]

same, I also use a mini starter from 92 f150 5.0. Replaced super mean green expensive starter that literally chewed itself apart.

 

[EPB72]

Does your starter high current wire run through that fuse it should not,,, starter inrush current can exceed 1600 amps ,,(a Honda 4 cylinder can exceed. 1500 amps ) ,, that fuse is a quick blow ,, I have yet to see any oe vehicle fuse the starter high current cable .. ??

 

[Broncobowsher]

What amperage was the mega fuse?
Fused starters are rare. I might know of a couple vehicles with them, but would have to double check.

I thought this was going to be someone put a 100A fuse on the 130A alterntor again. Of course that will blow.

 

[cldonley]

Does your starter high current wire run through that fuse it should not,,, starter inrush current can exceed 1600 amps ,,(a Honda 4 cylinder can exceed. 1500 amps ) ,, that fuse is a quick blow ,, I have yet to see any oe vehicle fuse the starter high current cable .. ??

What amperage was the mega fuse?
Fused starters are rare. I might know of a couple vehicles with them, but would have to double check.

I thought this was going to be someone put a 100A fuse on the 130A alterntor again. Of course that will blow.

It's a 175 amp mega fuse between the battery and the post on the starter solenoid. Really surprising to me that it is bad, kinda makes me think it was a bad fuse in the first place. I was leaning toward replacing the starter with a gear reduction starter anyway because the old starter sounded terrible, although it seemed to work fine. I guess the bottom line is I still don't really know why it gave up. I wouldn't expect it to be the alternator because the engine wasn't running. The only thing drawing power was the starter when it gave up. I've had an aircraft alternator fail and runaway-amps through the roof. Never had that kind of failure on a wheeled vehicle, and again, it wasn't running when the fuse quit. Another interesting thing is the fuse shows no visible sign of failure. I plan to drill out the rivets and see what it looks like on the inside. I tested it with two different multimeters and there is no continuity through it. I suppose I should add that the charging system was working fine before the fuse gave up.

 

[ba123]

Yeah, a starter does not need a fuse and should not have one.

Alternator yes, but needs to be far over the amp rating. For example, I have a 200 amp alternator, and a 250 amp fuse.

 

[cldonley]

Yeah, a starter does not need a fuse and should not have one.

Alternator yes, but needs to be far over the amp rating. For example, I have a 200 amp alternator, and a 250 amp fuse.

My alternator is a stock 130 amp and I’m running a 175 amp fuse. The only thing operating when the fuse quit was the starter.

 

[ba123]

My alternator is a stock 130 amp and I’m running a 175 amp fuse. The only thing operating when the fuse quit was the starter.

Maybe I’m confused.

Is the fuse on the starter line or the alternator or maybe they are shared?

Starter should be direct from the battery to the starter (or start switch) and no fuse. Alternator should be starlight to battery with a fuse. Different connection even if to the same positive post.

When you turn the engine with the starter. Your alternator is on. Just saying. Also anything in the ACC and Start positions would be on as well unless you had things disconnected in testing.

Again, no fuse should be on the power line to the starter. If you’re saying that you have it all this way and the fuse between your alt and battery blew?

If so, I’d look for a short in your alternator wiring.

If I’m totally way off maybe say exactly what is on the line of that fuse that blew.

Sorry if you said this and I missed it. I’ll reread it you tell me to.

 

[Oldtimer]

It's a 175 amp mega fuse between the battery and the post on the starter solenoid.

I think this is what you have?
Starter thru fuse.

I think this is what you want?
Alternator thru fuse.

 

[ba123]

Exactly

 

[cldonley]

I think this is what you have?
Starter thru fuse.

View attachment 958219

I think this is what you want?
Alternator thru fuse.

View attachment 958220

Yep. You are correct. I have seen the light.