Mercruiser 7.4. Accidentally reversed battery polarity and now no ignition?

[Dejay]

Thank you BT Doctor. That gives me a lot to work with.

Hopefully can get down there this weekend and have a go.

I will report back with the results.

 

[stwischu]

Similar problem. I used a volt meter to trace the power. Saw no power at all at the 50 amp circuit breaker. Just pushing the red button doesn't tell you anything. If you aren't getting power on EITHER side of the breaker, then its irrelevant. I found a block fuse bolted right onto the starter hot terminal. It separates the big cable from the battery from the wires going to the 50amp circuit breaker and alternator. It actually saved my a** since without this fuse my alternator would have fried. There is a picture of it in this email chain already. I ordederd a new one from amazon for $28. 90 amps.

 

[Dejay]

Thanks again everyone.
i have the engine running now.
As in the earlier post, I jumped a power supply to the red on the ignition key. This gave me the start warning buzzer, fuel pump and sometimes a click from the relay. After an hour of mucking around, on one start attempt, the starter engaged. Very exciting but that was the last time for another 30 odd minutes. So I have a fault that only shows every now and then.
The good news is, 40 minutes later, she was running and I was very happy about that.
So in the next few weeks, I can drive it around to the mechanics where she will get services and anti fouled.
Hopefully, it is a fuse and a faulty start relay. It also could be a starter motor problem, but either way, I will post to let you all know.

Thanks again everyone.

 

[JimG]

Thanks for the update!

 

[Dejay]

Thanks for the update!

No probs. I run a few forums and things I hate are titles with crappy info like "I need help" and people that post "it's ok, I found the answer by myself".
All that aside, without everyone's great suggestions and help, I would have had to get a mobile marine mechanic to sort the issue out. I have little doubt, this would have cost me a bomb as they can say it was anything and charge accordingly.
I really want to thank DOC as his advice with the power to the key with the purple wire got me through the issue.
So when I have the full solution, I will change the title to prob/ solved and once again, thanks to all because everything helped and your all champions.

 

[Dejay]

Re: Mercruiser 7.4. Reversed battery polarity and now no ignition? FIXED 90amp fuse

An update. As reported earlier, I hot wired the ignition and got the engine running. It took a a little while and I used a few squirts of airo start, "not sure of the spelling" through the air intake.
Last week, got up early and cruised the 30km / 19 miles to the next bay up to get her serviced, anti fouled and repairs.
It seems the problem was the 90amp fuse on the starter as a few mentioned. Now the strange thing about this is, I made it 19 miles and 9 of that was deep sea.
Maybe it was not completely burnt through? I really can't say. But after I left it, the mechanics could start the engine but it would instantly stall after ignition release. But all aside, I'm heading out hopefully for a run this weekend and will know if the fix worked or not.
She looks good all cleaned up so very happy.

Thanks again everyone. Will post if the problem comes back..

 

[mistercomputerman]

You mean this fuse?