Proper way to wire a kill switch on Thunderbolt IV

[Joshto]

Hi Folks,

I just asked this question on another thread but since this is newer, though I'd have better chances of getting help.

The question is about the kill switch installation on the purple wire.

I noticed the Purple cable (ignition) is as thick as the Red (battery) which seems to suggest it handles high current. The Seadog Kill switch is rated for 5 Amps max. Is that enough to withstand the ignition current plus whatever accessory feeds from the purple wire when the engine is running? I'm afraid the switch might melt in the middle of the lake.

Thanks
Josh.

 

[Chris1956]

What engine are we discussing? Thunderbolt was the name of ign for OBs and I/Os.

 

[Joshto]

It's an I/O Merc 3.0 (140HP)

 

[Joshto]

What engine are we discussing? Thunderbolt was the name of ign for OBs and I/Os.

It's an I/O Merc 3.0 (140HP)

 

[alldodge]

Take the purple wire coming off the key switch and put kill switch in it. Kill should break the connection when pulled

 

[Joshto]

Take the purple wire coming off the key switch and put kill switch in it. Kill should break the connection when pulled

Thanks but that's not my question. My question is whether a 5 amp rated kill switch would withstand the current drawn by the engine and instruments.

 

[alldodge]

Thanks but that's not my question. My question whether a 5 amp rated kill switch would withstand the current drawn by the engine and instruments.

Sorry, no 5 amp is not enough. Look at your ignition fuse, its either a 15 or 20 amp, I would use a 20

 

[Joshto]

Sorry, no 5 amp is not enough. Look at your ignition fuse, its either a 15 or 20 amp, I would use a 20

Thanks. They seem difficult to find. I found a 12 amp kill switch...nothing above.

 

[alldodge]

Use the 12 I guess

 

[froggy1150]

What is the wire size? 10 guage? 12, 14? Your switch should be rated for the max current the wire can carry.

 

[froggy1150]

This chart should get you close

 

[Joshto]

This chart should get you close

I think mine is 12. Based on the chart it would be 10A @ 4.6 meters... which seems low for the ignition plus instruments.

 

[froggy1150]

If you have an amp meter you can check draw. If not try throwing a 5 amp fuse, then a 7 amp and then a 10 amp. The 5 should blow. Swap to the 7 and see if that blows. And same with the 10. You will have to run for a min or three but its a rough way to see amp draw. So if the 7 either gets hot or blows and the 10 dont you have a 10 amp circuit and things need to be rated at or above that threshold.

 

[Joshto]

Had the chance to measure the current drawn by the ignition system. It's about 3.7 amps ( ignition only without instruments)

Installed the seadog switch (which is actually rated 10amp); it works like a charm.