Topic: CB750

[horrorbiz]

I recently lost a good deal of my wiring when my reg/Rec combo until caused a fire on my '78 CB750k. I've been learning how to work on things but I've only done a little bit in regard to electrical things. There's even a chance the fire had something to do with me doing something incorrectly... But the bike has been running great for a while.

Over the past year and a half I've been trying to simplify my bike to the bare minimum in a sort of cafe/street tracker build. I'm going to need to rewire the bike and I'm trying to find a resource for a novice like myself. I want to figure out the bare minimum I need for the bike to run (and be street legal).

Does anyone have any resources, suggestions, or tips? I've been looking at maybe trying to start from scratch with a Motogadget M-Unit. But as I said, I'm a beginner so I welcome any feedback.

[horrorbiz]

Yikes, sorry about the title, I accidentally sent the post before I finished.

[riffman12]

geez what happened exactly? The reg/rec unit caught fire? or something else?

What kind of battery were you running?

Had you tested your charging system prior to the fire to make sure it was operating correctly?

[horrorbiz]

geez what happened exactly? The reg/rec unit caught fire? or something else?

What kind of battery were you running?

Had you tested your charging system prior to the fire to make sure it was operating correctly?

I'm not exactly sure, this setup had been running fine for months. The reg/rec burned up and took a bunch of wiring with it. I was away for a couple weeks and the battery had died, I hooked it up the tender over night as I've done in the past. The next day I disconnected the tender and the bike started right up, but almost immediately smoke started pouring out from behind the side cover.

[horrorbiz]

geez what happened exactly? The reg/rec unit caught fire? or something else?

What kind of battery were you running?

Had you tested your charging system prior to the fire to make sure it was operating correctly?

This is the battery I'm running: BS Scorpion 12v 210 CCA AGM ATV & Motorcycle Battery

[horrorbiz]

Here's a very simple diagram of the bare essentials.

I am a huge fan of the MotoGadget stuff, even for novice installers. BUT, you need to decide and determine some stuff first.

You MUST investigate the harness from your stator (under the left side cover) to insure its healthy and undamaged. You need to inspect and test your battery to determine if the issue was caused by a defecting charger, or a bad connection, or a damaged battery. Then, when you know you have a safe platform to re-wire from, go forward.

If your intention is to remove the auxiliary functions (Indicators, horn, electric start, gauges, etc) and run a really bare bones bike, then a MotoG is not worthwhile. Mostly, its huge benefits come from having an integrated central location to program and control these functions. Pointless if you're removing them.

If you opt to retain all the functions, and decide to re-wire, I am huge proponent of the unit then. It runs about $300, you also want their AUX plug connector, but don't buy the M-button. You can replace your handlebar controls with simple momentary switches to further simplify and ease your install.

But please check your bike top to bottom to identify the cause of that damage!!!!

Thanks so much, this is hugely helpful. I will look over everything. I just thought of something... I may have accidentally left the switch to start the bike on. I don't know for sure, but possibly after trying to start the bike for a while and failing I may have just forgotten. Could that have caused it to overheat?

When I say bare-bones I'm referring to the minimum I need to get through my MA inspections... Which requires lights/signals/horn. So it seems like the m-unit might be a good option for me.

[horrorbiz]

If the key is on, the coils are energized. This can cause the cols to overheat, but I'm not sure about the Reg/Rec being damaged as a result. I would suspect a bad charger as the culprit or incorrectly attached charger.

Hmm well the charger was a cheap one, but seemed to do the job in the past. It has a feature where it will flash if connected incorrectly.

[greenjeans]

Just my 2c...

For the cost of an M-Unit (which are awesome)  You can buy a new harness:
http://www.partsnmore.com/parts/?q=wiring+harness )

and new handlebar switches (to match the harness):
http://4into1.com/reproduction-left-switch-assembly-35200-404-671-honda-cb550-cb750/
http://4into1.com/reproduction-throttle-switch-assembly-35300-341-671-honda-cb550k-cb750k/

new wiring from the alternator to the harness (alternator stator wire harness)
http://www.partsnmore.com/parts/honda/cb750k/?

filters[category]=electrical&filters[fitting]=custom&filters[page]=2

and a combo rectifier/regulator from Mikes:
http://4into1.com/ricks-motorsport-electrics-honda-rectifier-regulator-combo-cb350-cb400-cb500-cb550-cb750/

Little bit more adds aftermarket coils - althought the stock Honda coils rarely fail.

Granted, it's not a harness etc for your specific year, but the motor don't know.

[USMC5811]

Check your battery wires.
Same thing happened to my wiring (no fire, thank goodness) when battery grounded against the frame. Lost my entire wiring harness plus regulator and rectifier.


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[Phinn]

Just my 2c...

For the cost of an M-Unit (which are awesome)  You can buy a new harness:
http://www.partsnmore.com/parts/?q=wiring+harness )

and new handlebar switches (to match the harness):
http://4into1.com/reproduction-left-switch-assembly-35200-404-671-honda-cb550-cb750/
http://4into1.com/reproduction-throttle-switch-assembly-35300-341-671-honda-cb550k-cb750k/

new wiring from the alternator to the harness (alternator stator wire harness)
http://www.partsnmore.com/parts/honda/cb750k/?

filters[category]=electrical&filters[fitting]=custom&filters[page]=2

and a combo rectifier/regulator from Mikes:
http://4into1.com/ricks-motorsport-electrics-honda-rectifier-regulator-combo-cb350-cb400-cb500-cb550-cb750/

Little bit more adds aftermarket coils - althought the stock Honda coils rarely fail.

Agree 100%.  I replaced my entire electrical system with almost this exact set, and it works perfectly. 

[scottly]

geez what happened exactly? The reg/rec unit caught fire? or something else?

What kind of battery were you running?

Had you tested your charging system prior to the fire to make sure it was operating correctly?

I'm not exactly sure, this setup had been running fine for months. The reg/rec burned up and took a bunch of wiring with it. I was away for a couple weeks and the battery had died, I hooked it up the tender over night as I've done in the past. The next day I disconnected the tender and the bike started right up, but almost immediately smoke started pouring out from behind the side cover.

Did you disconnect the battery for charging, then reconnect it before starting the bike? The most common cause of rectifier melt-down is reversing the polarity of the battery connections. My opinion of the M-unit is that it's a waste of money, and only adds confusion and complication to an other wise simple wiring scheme; I fail to understand the benefit of running a wire, say, from the headlight switch, to the M-unit, and then from the M-unit back to the headlight. Why not just run the wire from the switch directly to the headlight? Then again, what do I know? I only have 2 electronics degrees and 50 years experience with systems ranging from 8-track tape decks to industrial computers to nuclear reactors.

[horrorbiz]

Thanks everyone. I got started today removing the damaged wires, which turned out the be the majority of the main harness.

[Phinn]

Thanks everyone. I got started today removing the damaged wires, which turned out the be the majority of the main harness.

Might it be advisable to get a new harness?

[horrorbiz]

Thanks everyone. I got started today removing the damaged wires, which turned out the be the majority of the main harness.

Might it be advisable to get a new harness?

I think that's probably going to be the plan.

[USMC5811]

$99 from Vintage750.com


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