Honda 750A Hondamatic Park Brake Switch problem

[captnicker]

Honda 750A Hondamatic , 1977
Park Brake Switch problem 10-01-16

I've recently found the reason why my brake lights do not work. The automatic models have a requirement for an emergency brake because they cannot be left in a gear when parked. Honda thought it prudent to put a light on the right instrument cluster to indicate that the park brake is on. This is helpful when diagnosing why your bike doesn't move when put into drive and the accelerator applied.
This switch is located above the rear brake arm and enters the aluminum support housing.It connects power to the lamp. Only the Automatic specific wire diagram has this info which I found in the Clymer manual only. This is about the only worthwhile info I actually found in this marginal manual. Honda's shop manual doesn't even have a wire diagram.

I digress here. It turns out that the switch has an additional function (hence the 4 wires going to it). When the park brake is on, the circuit to tail brake light is opened.I guess this allows the park lights to illuminate with parking brake on, without the added current draw of the brake lamp.If you were disabled along a busy motorway,on a hill, at night, perhaps this might help.

Honda seems to have gone to a lot of trouble making this bike lighter after that enormous automatic transmission was added.Things like the aluminum wheels comes to mind. They also made this brake switch housing out of aluminum. This might have worked, but the addition of non aluminum electrical parts inside made for exceptional galvanic corrosion inside. When I removed the switch boot,it literally fell apart into white powdery residue with some corroded metallic connectors still attached to the 4 wires.

Naturally, this part is no longer available. The short production run of the CB750 Hondamatic was no doubt the real cause. The corrosion problem was never addressed by Honda and now the spares are all gone.

What to do? What to do? If anybody has some thoughts on this I would like some advice. The used ones I've seen online (EBAY) come with the caveat "what you see is what you get"and no guarantee to work. None have the boot removed to see the insidious corrosion that probably lurks underneath. All do have a price tag of $100 plus US dollars plus shipping. Taking a risk to purchase and look under the boot doesn't seem worthwhile.

I've thought of making my own simple grounding switch from the remnants of the old one. It could operate two 12v auto relays to connect power to the indicator lamp and another to disconnect the two wire circuit leading to the park brake. But I am not a machine shop or electrical engineer. This task should have been handled by Honda.
Any solutions will be most appreciated!

 

[Strummer737]

Honda 750A Hondamatic , 1977
Park Brake Switch problem 10-01-16

I've recently found the reason why my brake lights do not work. The automatic models have a requirement for an emergency brake because they cannot be left in a gear when parked. Honda thought it prudent to put a light on the right instrument cluster to indicate that the park brake is on. This is helpful when diagnosing why your bike doesn't move when put into drive and the accelerator applied.
This switch is located above the rear brake arm and enters the aluminum support housing.It connects power to the lamp. Only the Automatic specific wire diagram has this info which I found in the Clymer manual only. This is about the only worthwhile info I actually found in this marginal manual. Honda's shop manual doesn't even have a wire diagram.

I digress here. It turns out that the switch has an additional function (hence the 4 wires going to it). When the park brake is on, the circuit to tail brake light is opened.I guess this allows the park lights to illuminate with parking brake on, without the added current draw of the brake lamp.If you were disabled along a busy motorway,on a hill, at night, perhaps this might help.

Honda seems to have gone to a lot of trouble making this bike lighter after that enormous automatic transmission was added.Things like the aluminum wheels comes to mind. They also made this brake switch housing out of aluminum. This might have worked, but the addition of non aluminum electrical parts inside made for exceptional galvanic corrosion inside. When I removed the switch boot,it literally fell apart into white powdery residue with some corroded metallic connectors still attached to the 4 wires.

Naturally, this part is no longer available. The short production run of the CB750 Hondamatic was no doubt the real cause. The corrosion problem was never addressed by Honda and now the spares are all gone.

What to do? What to do? If anybody has some thoughts on this I would like some advice. The used ones I've seen online (EBAY) come with the caveat "what you see is what you get"and no guarantee to work. None have the boot removed to see the insidious corrosion that probably lurks underneath. All do have a price tag of $100 plus US dollars plus shipping. Taking a risk to purchase and look under the boot doesn't seem worthwhile.

I've thought of making my own simple grounding switch from the remnants of the old one. It could operate two 12v auto relays to connect power to the indicator lamp and another to disconnect the two wire circuit leading to the park brake. But I am not a machine shop or electrical engineer. This task should have been handled by Honda.
Any solutions will be most appreciated!

Hello. First time posting. I was wondering if you ever found a solution to this issue. I'm in the middle of the exact same problem and it's driving me nuts. Thanks.

 

[amc49]

Entire manual here and it DOES have the wiring diagram, the last 2 pages.

http://manuals.sohc4.net/cb750a/service_manual/SM750A.pdf

Let it load then copy it to disc using one of the icons on the right side and permanently yours then.

Not hard figuring that parking thing out at all.

 

[Strummer737]

Thanks. I already have the shop manual and wiring diagram. The problem is that I'm not smart enough to figure out how to bypass a broken parking brake switch on my own. I was hoping someone would have specific instructions of how to do it.

 

[amc49]

If you are looking to just get brake light working normal then tie the two right hand wires together in the schematic, both are green/yellow I'm thinking. Brake light will then work like a bike with no switch.

 

[captnicker]

No luck finding a new switch

I can't find a new switch to replace the corroded one. I did find a switch that has potential on EBAY. It has the correct electrical properties in that it has two circuits (4 Wires) that are activated by a push button. It will open one circuit and close the other with a push and reverse that situation when pressure is released. The problem is that it requires an adapter to fit it to brake housing and allow for adjustment of the push button. It will require a metal lathe to produce this . Not very cost effective to hire out to a local shop for this, considering the small quantity that will be needed for this limited production model.
I have done what AMC49 suggested and just connected the grn and ylw wires together. This will give you back your brake lights. The Park brake indicator light on the panel will not work like this, so remember to release the park brake before departing. Be sure to insulate and tape the two other wires off , as they are not used now to activate the park brake indicator lamp. The Wiring diagram that AMC49 listed is great (thanks) and might help to keep track of the wires here.

 

[amc49]

There would be a number of ways the switch can be imitated in action but all would require careful thinking to get the physical characteristics just right to work reliably. It all hinges on figuring out how to use the action of the rachet lever end that does the moving to activate the switch, which could also be more than one type depending on how you work that out.

A simple 2 wire brake light switch with a long wire to activate it might work simply to work the park light, the wire extending down in the hole to a hole drilled in the rachet lever tab. Might have to use a relay to flip the electrical from on/off to off/on. You'd need to waterproof the access hole too but Honda didn't do that much better than you could.

There's ways if somebody wants to bad enough. I could do it with a drill and some hardware bits.

 

[amc49]

Now you're making me think. You don't even need the 4 wire switch, you use a 2 wire like normal brake switch and then a relay added to flip the two wire into a 4 wire action. The relay rests off with brake light wires connected and activated opens them to activate park light. Easy peasy. Requires a 6 pin relay.

 

[wingedwheel]

This is good info. I just started tearing down a '78 I bought and am almost to that housing and switch. I was going to wait but now I have to know! The bike sat for 26 years so there is plenty of other corrosion, hopefully not there.