Merc 170 blowing ignition fuses

After running all day hardcore on the lake with no problems we get back to the idle zone to recover the boat and it just dies. Checked ignition fuse (next to starter switch, 25 amp) and it was blown. Put another in. Immediately turning ignition to on position (not to start, just the on) it blows again. Kept blowing them, about 4 total and instantly. They are WAY too hot to touch. Any ideas?

I'm just confused because it ran awesome all day, then just died at the end, causing us to row and push on to trailer.

Note: I did remove the original igntion switch and put in a 50A toggle switch for "engine circuit" (don't know the term) and a 65A push button switch. I did this because I'm a sucker for losing keys!

Anyways this combination has been used for the last 4 trips with no problems with this toggle and push button start.

Throw me some ideas!

Oh yeah other key info: installed Pertronix ignition so from ignition toggle switch, I ran a dedicated 16g wire to the + side of coil. I also cut the resistance wire going from choke to coil. There were two wires, one purple and one purple w/ yellow stripe. I cut purple. Was that the right one?

you must have , the resistance wire to the coil. the pertronix ignitor feed should be made at the choke electrical connection which is the full 12volts.

I suspect you damaged the ignition coil as this OEM coil requires a 2 ohm resistance to the coil plus side which is the primary of the ignition coil .

My fault for lack of info. With Pertronix I changed coil as well to Flamethower coil. Has internal resistor and needs full 12v supply.

with that the case then recheck your new wiring. did you properly use the correct lugs / crimping tool and use a heat shRink on these lugs to prevent shorting. also the coil connection is very close to the metal ground. did you use the proper lug for the coil connection ?

I used all the right lugs but no heat sink. I've never heard of using one. Know where I can get one? None of the wires on there now have a heat sink...

Disconect the + coil wire, try to restart if fuse blows then disconnect choke purple wire and coil +, if fuse still blows look at starter connections........disconnect the big main harness connector if it still blows look at dash wiring.

Not heat sink; heat shrink tubing. Some connectors come with it. You can get it at any autoparts store.

kghost, thanks for that! that's a great starting point! I will check all that probably tomorrow afternoon and let you guys know. Now can you tell me where exactly the main harness is? I have yet to stumble across it...thanks!

Guy, didn't know of such a thing but I will definitely get some and rewire it to be safe! again tomorrow afternoon.

Ok boat was at dad's (he's got more time to investigate). he checked all the wires he could and said he couldn't find any problems. Then he noticed that the fool (previous owner) that installed the radio, wired the power directly up to the ignition fuse. We've been having radio troubles (power cutting on and off) so he unhooked the radio power and started the boat up with no fuses blowing. we're gonna rewire the radio power on to an accessory power source.

Ok I went to dad's today to work on the boat. Thought it was in the panel somehow but it's not. Pulled the panel, fixed the ghetto job that the previous owner had. Removed the wire from ignition switch to the coil. Had great power, good lights, radio, etc. Turned over fine but would not start.

Attached coil wire and didn't blow the fuse, but it was getting hot enough that the fuse was smoking and getting ready to blow. So I took the ignition wire off (I even replaced the wire so I can guarantee that there is no shorts) and back to great power. So I then tried to splice a wire off of the purple wire from the choke (not resistance wire) and it did the whole nearly blowing fuse thing again.

Please help!!! Quick rundown again: Pertronix Ignitor II with Flamethrower coil. From coil negative I have a gray wire and the black wire from the ignitor. From coil positive I have purple wire w/ yellow stripe and red wire from ignitor. Engine won't start unless direct 12v source is hooked to coil positive but when I do that it blows the ignition fuse.

Hmm interesting. Pertronix site said that I shouldn't deliver more than 4 amps. I had ASSUMED that the guy gave me a 3ohm coil like I asked so I didn't put a ballast resistor on. Come to find out, he sold me the 1.5ohm coil made for 8 cylinders. So I think I need a 1.5ohm ballast resistor.

Does this sound like it might fix?

Ask them to send you the correct coil.

The Pertronix requirement is less than 3 oms resistance. But if the guy gave you the wrong coil get the right one. Check for pinched wires in your installation. The ignitor is hooked up right, it sounds like the coil is not. Possibly bad ignition switch?

Alright guys thanks for all the help. Turns out I pulled the distributor cap and moved the rubber grommet that held the Ignitor wires in place in the exit hole of the distributor. The Red positive wire was pinched so hard that it seemed to be only holding on by a strand or two of copper. It nearly instantly broke in half. So I soldered, heat shrinked the wire, reinstalled, reinstalled the 12v wire from the ignition switch and all is working great! Thanks puget for the idea!!

J-cat gets the credit for the pinched wire theory. Glad to see it was an easy fix and you can go out and enjoy your boat now.