Battery connection on new-to-me 1974 MKII Commando

J

jandrea

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Jul 11, 2014
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Greetings all,

First Post...
This summer I purchased an original condition 1974 Commando. I believe it's a MKII, since it has a 315XXX serial # and metal airbox.

I do have all of the workshop manuals, but just looking for some confirmation on hooking up my battery, since it doesn't have one.

It seems to me that I just have to connect the one red terminal (connecting two red wires, circled in yellow) to "+" on the battery, and from the initial research I've done, I need to connect the brown/blue wire (circled in yellow) to a section of 14 gauge wire, with 15amp fuse, to the "-" terminal of the battery and I'm good to go. Can anybody confirm this?

I also have a question about the wires that are hanging without connections.... circled in blue.



Thanks!
Jason
 
jandrea said:
It seems to me that I just have to connect the one red terminal (connecting two red wires, circled in yellow) to "+" on the battery, and from the initial research I've done, I need to connect the brown/blue wire (circled in yellow) to a section of 14 gauge wire, with 15amp fuse, to the "-" terminal of the battery and I'm good to go. Can anybody confirm this?
Click to expand...

Assuming the electrical system is still the original positive earth/ground then yes, red connects to battery positive and brown/blue to negative.

jandrea said:
I also have a question about the wires that are hanging without connections.... circled in blue.
Click to expand...

It would help if you could say what the colours are or might be.
Are they white/purple and white/red by any chance? If so then they don't connect to anything.
Or, a white and a (faded?) light green/brown (flasher relay)?
 
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Agree you should confirm it has not been converted to negative earth setup. I'd assume this can be done by using an Ohm meter or test lamp and battery, to see if the red wire terminal is in electrical contact with frame/Z-plates while the negative terminal is not.

There are a number of unused connections on the MKII wiring harness, as the harness was also used on later MKIII e-start bikes so had provisions for added components.

Be sure to thorough de-rust/clean all the lucas bullet connectors. Loads of examples of them fracturing within plastic covers, leading to poor unreliable contacts . It harness shows too much damage, just source a new one. Much easier to do now than after bike is all together.
 
When you do finally put the battery in, invest in the factory hold-down and the associated rubbers. They are available and not expensive.
 
Also be aware that US automotive fuse ratings and the ratings used for British bikes are not the same, slow blow vs. fast blow.
 
Tornado said:
There are a number of unused connections on the MKII wiring harness, as the harness was also used on later MKIII e-start bikes so had provisions for added components.
Click to expand...

The 850 Mk3 harness is much different to the Mk2 harness and certainly not used on the Mk3 but the Mk2 harness can have the previously mentioned and unused (on the Mk2) starter solenoid WP and WR wires.
 
Thomasa said:
Also be aware that US automotive fuse ratings and the ratings used for British bikes are not the same, slow blow vs. fast blow.
Click to expand...

The original Lucas fuses were marked and referred to by the blow rating.

The original glass fuse and what's stated in manuals and handbooks was "35A" blow, 17A continuous although 15A (or 20A) continuous (blade fuse etc.) can be used.
Battery connection on new-to-me 1974 MKII Commando
 
L.A.B. said:
The original Lucas fuses were marked and referred to by the blow rating.

The original glass fuse and what's stated in manuals and handbooks was "35A" blow, 17A continuous although 15A (or 20A) continuous (blade fuse etc.) can be used.
Battery connection on new-to-me 1974 MKII Commando
Click to expand...

I've already learned some very important concepts regarding the electrical systems on the British bikes. I had never even heard of a "positive earth" system before... and the differences with fuse ratings, etc... when compared to the US. I'm in Minnesota, and have a background in vintage Japanese bikes and my '69 Plymouth Barracuda. Thanks very much and glad to be a part of this community! I've wanted a Commando for decades. Let the learning and contributing begin 👍
 
jandrea said:
I've already learned some very important concepts regarding the electrical systems on the British bikes. I had never even heard of a "positive earth" system before... and the differences with fuse ratings, etc... when compared to the US.
Click to expand...


Many older vehicles (not just British) had positive earth/ground electrics but it doesn't require any radical thinking to work on positive earth/ground systems it just has to be remembered that the polarity is the opposite of what you've become used to. :)
 
Thomasa said:
When you do finally put the battery in, invest in the factory hold-down and the associated rubbers. They are available and not expensive.
Click to expand...
Velcro works great as long as you secure the battery case in perpendicular planes.
 
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Looks like a lot of the original connectors have been replaced with crimp connectors so someone has done some fixes, crimp connectors are good if the right crimping tool have been used, I use a ratchet crimping tool for all my crimp connectors as it don't over crimp the connectors but the ones on your bike look like they been done right.
If you connect the wrong polarity your wiring will smoke real quick.

Ashley
 
....and GREAT JOB 🤝knowing when to stop, and get information before causing damage. We get a LOT of first posts: "so I put in a new battery, smoke came out of the thingy (!) and it won't start."
🤡🤣
 
L.A.B. said:
Only two that I can see in that picture.



It should just blow the fuse.
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Yes Les only two in the pic but could be more elsewhere in the 48 year old wiring, and yes it will blow the fuse but might get a little smoke and smell from the wire connector when touching the wrong battery terminal before the fuse blows.
 
To verify positive ground, do a connectivity test between the red wires and the cylinder head

And this is good ref.

3-1972-onwards-Commando-Original.png
 
ashman said:
Yes Les only two in the pic but could be more elsewhere in the 48 year old wiring, and yes it will blow the fuse but might get a little smoke and smell from the wire connector when touching the wrong battery terminal before the fuse blows.
Click to expand...

Having done the same myself on the odd occasion when I've failed to switch my brain over to working 'positive earth' then the fuse has blown immediately the wire terminal touched the battery terminal with no other damage. :)

TomU said:
To verify positive ground, do a connectivity test between the red wires and the cylinder head
Click to expand...

The red earth/ground is attached to what should be the rectifier '+' stud connection, therefore, probably is positive earth/ground but still wise to check.
 
L.A.B. said:
The red earth/ground is attached to what should be the rectifier '+' stud connection, therefore, probably is positive earth/ground but still wise to check.
Click to expand...
Yeah, you never know what's going on behind the electrical tape curtain. Probably also good to check the negative side against ground as well for any shorts
 
It seems unlikely to have been converted to negative ground. If one were to convert to negative ground would you not need to reverse the zener polarity? The stud would have to be electrically isolated from the frame/z-plate and a wire run from the stud to the rest of the electrical system. But then you'd lose the heat sink. That would be a dead giveaway... unless there is a negative ground Lucas zener that I don't know about, which is entirely possible. Of course someone could have used a different zener but I suspect it would look different.
 
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