Fuse box woes

[alexdecker]

Hey all

Alright, trying to make sense of my fuse box. Before taking apart the bike, it ran with this setup to no apparent problems. My fuse box looks a little battered, but it should work.

Now, from what I know, my 550F2 from 1978 should have a fuse configuration from left to right of 5A for tail, 7A for head and 15A for main.

The labeling on my fuse box says they should all have 7A though? And to complete my confusion, it ran with a setup from left to right of 20A, 10A and 10A.

I just completed the wiring and turned the bike on today. No power. Checked the fuses. The 10A in the main holder is bad. The other two are still good.

Don’t know how it could run with a 10A in the main to begin with. But it’s blown now.

Can anybody make sense of this? Or is my idea of the correct setup mistaken?

[McCabe-Thiele (Ted)]

Looking at that fuse holder I would be looking for a new one if they are available as a pattern part or a used one in good condition.

[alexdecker]

Looking at that fuse holder I would be looking for a new one if they are available as a pattern part or a used one in good condition.

Yeah, it had a bad burn. Should work though! Don’t know about that labeling though. The box seems original, and so does the labeling.

[Bryanj]

Go to Hondaman he makes a plug n play blade fuse unit

[Oddjob]

IIRC you are right, 2 7a and 1 15a for the main.

I'm replacing mine with a Honda blade fuse one, my old one is in very good condition (AFAIK) if your interested. Same bike 550F2.

[bruxby-clive]

I think you should also check the loom over as it is probably corrosion or old wiring that has caused resistance within the cables and generated heat at the weakest point, causing the fuse holder to melt.

[deltarider]

I think you should also check the loom over as it is probably corrosion or old wiring that has caused resistance within the cables and generated heat at the weakest point, causing the fuse holder to melt.

This ^ is repeated over and over again. After 46 years, I still don't have indication I have to check the loom and/or its connectors in total. I've had two issues: fuses and their clamps, which can be easily fixed and the IGN KEY switch which needed replacement. As far as the CB500/550 these seem to be the usual suspects.
Often overlooked: the NEG route, where the GREEN wiring is bolted to the frame.
Before disconnecting all connectors in the blind (the US method), which is very time consuming and brings the risk of ruining perfectly good connections, I'd rather do a proper diagnosis via a simple V₄ drop measurement. It tells you where to look.

[SteveW]

Check the outside of the loom for shiny areas / odd lines in the wrap as in the attached pic.
This is caused by a poor battery negative connection to the frame so the current uses the smaller green earth wires instead.
The green wires get very hot and melt into the other wires in the loom and also cause the tell tale shiny spots on the loom.
The pic is my loom.

[SteveW]

This was inside 

[alexdecker]

Thank you for the responses. I have got it all to work now, with the exception of two (important) things.

I have no spark in 1 and 4. And my hi beam is not working. I have the 550F2 with Off, P, On on the RH switch, and then Lo and Hi on the LH switch.

When I go to Hi Beam, the headlight shuts off. And after a while, it clips the first fuse (the tail one). It is the original Honda headlight.

I also don’t have spark in 1 and 4. I have power at the coils, at B/Y coming out of the coils and at B/Y at the points plate (tested by disconnecting them from the plate and measuring). I have also tested all the spark plugs, and they are all giving blue sparks. Just only in 2 and 3.

Any ideas?

[alexdecker]

Alright, took the fuse box off and apart, and someone had rewired the whole thing in reverse. So I put the 7A in the 15A spot and the 15A in the 7A. I don’t know if this has anything to do with the spark in 1 and 4 or the hi beam, but at least I fixed that now.

[K2-K6]

"I also don’t have spark in 1 and 4. I have power at the coils, at B/Y coming out of the coils and at B/Y at the points plate (tested by disconnecting them from the plate and measuring). I have also tested all the spark plugs, and they are all giving blue sparks. Just only in 2 and 3.

Any ideas?"

The points are switching the earth circuit and not as many visualise the positive voltage. Conceptually (with them closed) it's a bit like having a plug in a bathtub, the coils fill up with energy from positive feed all the time the earth is established, removing the earth causes the coils to discharge out through the plugs the energy that's been stored.

Unplug the points, put continuity metering on the points wire (not the coil wire) and check it across to the crankcase as it should have continuous route with points closed. When the points open that continuity MUST  be broken. If it doesn't do this the coils will never discharge a spark.

Check that firstly to see if those points are fulfilling that function before moving onward.

[alexdecker]

"I also don’t have spark in 1 and 4. I have power at the coils, at B/Y coming out of the coils and at B/Y at the points plate (tested by disconnecting them from the plate and measuring). I have also tested all the spark plugs, and they are all giving blue sparks. Just only in 2 and 3.

Any ideas?"

The points are switching the earth circuit and not as many visualise the positive voltage. Conceptually (with them closed) it's a bit like having a plug in a bathtub, the coils fill up with energy from positive feed all the time the earth is established, removing the earth causes the coils to discharge out through the plugs the energy that's been stored.

Unplug the points, put continuity metering on the points wire (not the coil wire) and check it across to the crankcase as it should have continuous route with points closed. When the points open that continuity MUST  be broken. If it doesn't do this the coils will never discharge a spark.

Check that firstly to see if those points are fulfilling that function before moving onward.

Unplugging the points and measuring them from the wire harness and grounded to the crankcase, I get continuity on both points when they are closed.

[K2-K6]

And what do you get when the points are open ?

You should loose continuity as soon as the contact faces move away from each other, this is what initiates the spark to come from the coils.

Effectively two states, continuity fills the coils ready to spark, breaking the  continuity makes the stored energy exit down the HT leads.

[alexdecker]

And what do you get when the points are open ?

You should loose continuity as soon as the contact faces move away from each other, this is what initiates the spark to come from the coils.

Effectively two states, continuity fills the coils ready to spark, breaking the  continuity makes the stored energy exit down the HT leads.

When the points are open, I don’t have continuity! So that should be good, right?