Coil to Battery - Direct Connection

[jrp]

I wired a more direct connection from the battery to the coils on my bike and am just sharing what I did in case anyone is interested. I am not suggesting anyone has to do this.

On the ST1100, the path from the battery to the coils goes like this (with the associated voltage drop):

Battery --> 30A Main Fuse --> Ignition Switch --> 10A Ignition Fuse --> Bank Angle Sensor Relay --> Stop/Start Switch --> Coils

On my bike, after doing the ignition bypass relay mod, it looked like this:

Battery --> 30A Inline Fuse --> 40A Relay --> 10A Ignition Fuse --> Bank Angle Sensor Relay --> Stop/Start Switch --> Coils

Now I want to eliminate the Bank Angle Sensor Relay and the Stop/Start Switch, which will leave me with this:

Battery --> 30A Inline Fuse --> 40A Relay --> 10A Ignition Fuse --> (New Relay) --> Coils

To eliminate the B.A.S. Relay and Stop/Start switch (and also preserve their functionality), I would need an additional relay. Here is the ignition configuration before I started. Note that the 40-amp relay is from the previously done ignition bypass relay mod (link here). Click picture to enlarge:



Here's what it looked like afterwards (click to enlarge):



Since I had already had a connection from the battery directly to the fuse box via the 40A relay, I ran a 14 gauge, tinned, high-strand-count wire from the fuse box to a 20A relay up by the coils. I moved the existing black wire going to the bank angle sensor and the bank angle sensor relay to the new wire. I also had to move the alternator sense wire onto the new wire as well.

In hindsight, had I not already done the ignition bypass relay mod, I would have done this and not touched the fuse box:

Battery --> 10A Inline fuse --> 20A Relay --> 20A Relay --> Coils

This would have taken enough load off the "Red Wire" to make it a non-issue without having to mess with the fuse box. A twofer!

The only somewhat tricky part to this mod is digging into the harness and splicing the existing ignition wire plus the alternator sense wire into the new wire. Remove the tape from the harness in the area shown here; the sense wire/ign wire splice is wrapped in blue tape:



Unwind the tape to reveal the splice and cut where indicated:



Lay out new wire and strip off about two inches of insulation:



Crimp the ignition wire onto the new wire (NOTE: I added an additional wire here for a future project; it is not needed):



Then crimp the sense wire:



Tape the splice, then re-tape the harness with two layers of high temperature resistant electrical tape.





Use a good quality relay. Here I'm using a Panasonic/NAIS 20A relay.



I attached the relay to the area of the harness that runs under the crossmember just in front of the carburetor rack.



Then plugged the new wire into the fusebox.

 

[v8-7]

That's how I used to "borrow" my parents 64 valiant.. long screwdriver across the starter terminals and away I went !

 

[Larry Fine]

Why feed power through two relays?

On my Nighthawk, I added an ignition relay that gets its power directly from the battery through a fusible link, and is controlled by one of the original coil wires. This is really no different from adding a horn relay.

I also added two direct-fed headlight relays, which I wired to drop out with the engine-kill switch turned off. I intend to do this when I add a fusible link and hot feed to the headlight relays on my ST1100.

 

[Larry Fine]

Brighter lights, hotter spark, louder horn, etc., and less load on original wiring.

 

[jrp]

Why feed power through two relays?

The 40-amp relay was already there from the ignition bypass relay mod. I wanted to preserve the functionality of the start/stop switch and the bank angle sensor relay. I don't know how to do it without adding a relay.

Also keep in mind that the 40-amp relay does not carry only the ignition circuit. It also carries the Position, Meter Light, Tail, Neutral, Oil, Temp, Tacho, Horn, Turn Signal and Brake (although it is not shown in the schematic).

 

[Larry Fine]

I wanted to preserve the functionality of the start/stop switch and the bank angle sensor relay. I don't know how to do it without adding a relay.

If you power the new ignition relay from either of the two original coil wires (black w/white tracer, if I'm not mistaken), it will either be energized or de-energized whenever the coils normally would be.

Again, just like adding a horn relay: The relay is controlled by the original circuit, and the load is now supplied directly from the source, switched by the relay, and turned on or off just like it was before.

Added: Looking at your diagrams, I am questioning why the power to the second relay passes through the first one. I would have left every other connection (tip-over, volt sense, etc) as they were.

In other words, the heavy wire you added feeding the new relay should come straight from the source, and only the coils themselves supplied through it. As if the relay coil was the ignition coils.

The bank-angle circuitry would merely be cutting power to the relay instead of the coils. The idea is to remove the ignition coils' current from the original wiring without changing how it functions.

 

[jrp]

If you power the new ignition relay from either of the two original coil wires (black w/white tracer, if I'm not mistaken), it will either be energized or de-energized whenever the coils normally would be.

Again,just like adding a horn relay: The relay is controlled by the original circuit, and the load is now supplied directly from the source, switched by the relay, and turned on or off just like it was before.

That is exactly what I did. Maybe you can rephrase your question.

 

[Larry Fine]

I'll try.

I would have run terminal #30 of the 20a relay straight from the battery (fused, of course), and left the rest of the circuit (bank angle and sense) on the wire from the 40a relay and ignition fuse.

 

[Larry Fine]

It's really a small criticism, more of a nit-pick. It's just what I would have done, and have done.

Added: What I mean is: I would have fed the 20a relay exactly the same way as you did the 40a relay, and I would have fed the coils exactly the way you did from the 20a relay. The only difference is I would have left the rest of the ignition circuit alone.

 

[jrp]

It's really a small criticism, more of a nit-pick. It's just what I would have done, and have done.

Added: What I mean is: I would have fed the 20a relay exactly the same way as you did the 40a relay, and I would have fed the coils exactly the way you did from the 20a relay. The only difference is I would have left the rest of the ignition circuit alone.

The original location of the sense wire monitors the voltage drop of the entire ignition circuit, which includes the coils. If you did that, then the coils would not be taken into account.

 

[jrp]

So I took Fat BaSTard out recently to stretch his legs. One thing that was noticeable was a smoother idle. The other was that I only had to touch the starter button and it immediately fired up. Normally it would take two or three cranks before firing.

I measured a charging voltage at the battery of 14.1v at idle. Previously it had measured at 14.4v. This makes sense given the lower resistance of the new wire.

Jeff