SF2 ignition wiring

[murphus]

In getting a 74 SF2 back up and running and replacing the Honda (!) ignition switch the previous owner fitted I find there are three wires to the switch; red, red and brown. One of the red wires is power to the switch. Looking at the wiring diagram, it looks like the second red wire runs to the regulator and from there powers the ignition and other accessories. The brown would appear to be for the tail light in the park position on the switch. What's odd is, the second red wire was not connected to the switch, only the power red and the brown. Further, a test shows that both the second red lead and the brown will power up the ignition when connected to power. That doesn't make sense, yet I don't find any indications of a further bodge? I'll be the first to admit that I find wiring diagrams hard to follow. Am I missing something obvious?
Richard

 

[Dellortoman]

Am I missing something obvious?

Maybe, maybe not. Depends which model Honda your switch comes from. How many positions will the key rotate?

A 3 wire ignition switch will normally (but not necessarily) have 3 key positions. - off, on and park. The key can be removed in the off and park positions. One wire is the power supply from the battery and the switch will energise only one of the other wires in each key position other than "off".

Some Honda ignition switches have 3 positions on, off and lock. The "lock" position engages the steering lock. The key can be removed in the off and lock positions. This type of switch energises both the non-battery wires in the on position.

Other Honda 3 wire switches only have on and off positions and no steering lock function. Sounds like you may have one of these. The on position energises both output wires as in your case. Each of the output wires supplying power (via the fuse box) to different functions. One wire powers the ignition and the other wire powers the accessories such as lights, horn, etc. These switches are generally found bikes with simple wiring systems (like trail bikes) that may come in different versions. Some with lights, indicators, etc., that are road registrable, and others without that stuff for purely off-road use. I presume it makes the switch more adaptable to the different wiring harnesses it may be used on.

Bottom line is that if you want a 3 position switch that'll operate in "park" mode (tail light and a low wattage lamp in the headlight switched on) you may need to find another switch.

Personally, I think the park light function is petty useless. Actually it's worse than useless because if you turn the key the wrong way to switch the ignition off, you could flatten your battery if you don't notice (in daylight) that the park lights are on. I presume it was only ever fitted because of some archaic requirement for vehicles to have park lights. But who ever uses park lights, even in their car?

 

[henrywillms]

If you are having a hard time following the wire diagram as it is hard to follow all the lines.....photocopy it aynd then use some different colored pens to color the relevant wires you are chasing down. 

 

[murphus]

If you are having a hard time following the wire diagram as it is hard to follow all the lines.....photocopy it aynd then use some different colored pens to color the relevant wires you are chasing down.

Good suggestion, and the issue turned out to be simple. The previous owner ran a jumper wire at the fuse box, jumping from where the red from the ignition switch joins the fuse box to to the brown to bypass a break in the single red lead to the tail light. The brown lead is power for ignition and the rest, the secondary red is just for tail lights when putting the key in the "park" position. So, instead of fixing the problem, they bypassed it. Typical. Fixed now.
Richard

 

[Dellortoman]

The only way to test any electrical component properly is to disconnect it from the rest of the wiring system first. I had assumed the switch was disconnected when you tested it.

 

[murphus]

It was disconnected, the issue I was trying to trace was the apparent redundancy in current to the system, which is supplied through the switch. What I did, and admittedly not a brilliant idea because of the unknown issue, was to jump power to the each of the two circuits -- ignition/accessories, and tail light only -- independently, which showed they were both doing the same job, which of course they shouldn't be. It hadn't occurred to me to simply look at the fuse box to see if anything was suspect.