Bad alternator, regulator or diodes?

Ran my 75' Mk3 for a ride the other day for the first timer, after a 20 mile ride loaded her up on the trailer and headed home from my chums place. Unloaded the bike and no start. Checked through the usual suspects, no spark. Added the charger and left her sit for 2 weeks maybe, only a few short seconds on the button and she fired right off. I checked voltage at the battery, under 14 volts at around 4500 rpm.

So Other than the Old Brits Power Arc I believe, everything is stock. The kind fella I bought the bike from installed the ignition and coil setup. The battery is a liquid type battery and maybe 1 -1 1/2 year old? New 4 brush presto light rebuilt starter and new heavy wire leads to the starter solenoid, starter and case.

I would like to add a new voltage regulator and have seen several mentioned here, could this be the issue aka diodes? I was hoping of determining that the alternator was ok. Any advice as to how to properly test the systems and diagnose the right part? Thanks as always for the great advice and comments. I love this forum. Ken

Recitfier = Wrecktifier . They were a bit suss. if battered theyre likely awol .

Alternator leads can crack at the chaincase grommet , or exiting encapsulation . the Zener Diode is the ' regulator ' Down on the footrest. Bleeds of excess ergs .

You have a voltmeter and it reads 14 V. at battery whilst running so sounds like power is getting back to the battery where it counts. So try other suspects such as cleaning up your kill switch contacts , cleaning up fuse contacts , cleaning up the grounds , cleaning up ign. switch , and eliminate the blue can capacitor too. :shock:

Torontonian said:

You have a voltmeter and it reads 14 V. at battery whilst running so sounds like power is getting back to the battery where it counts. So try other suspects such as cleaning up your kill switch contacts , cleaning up fuse contacts , cleaning up the grounds , cleaning up ign. switch , and eliminate the blue can capacitor too. :shock:

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Rebuilt the right switchgear and will go over all grounds and the small stuff. There is a fair amount of green in those plastic connectors my contact spray didn't remove. Can someone recommend a link or place on how to properly remove this blue capacitor? Any good recommendations for a real regulator?

Why not test your battery prior to replacing parts, especially as you are unsure of its age. Has it held the charge you put into it?
No harm and no expense in checking and cleaning all wiring and connections.

Get rid of that 43 yr. old blue can. Easy. Disconnect it by removing the red wire from the positive terminal . Heat shrink the wire end . Make a short wire shunt , to connect the remaining wires. There , you bypassed the damn thing. Green oxidations to connectors not good , clean up then re-connect tightly using an oxy-guard paste to prevent further oxidations. Or get to work this winter to snip off all brit cons. and fit modern. Should only take a year or so... :wink:

Torontonian said:

Or get to work this winter to snip off all brit cons. and fit modern. Should only take a year or so... :wink:

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Please don't do this. Most people do a piss poor job. More problems are created than solved. Also, there is nothing worse than a classic bike with those pink and blue flat-bladed connectors. The Lucas bullets and connecting sleeves are available and you really need to just replace the multi-wire ones under the tank and in the headlight shell. These are the ones where the metal is usually split inside and in pieces. A heat gun does a good job softening the rubber so the wires come out easier.

batrider said:

Torontonian said:

Or get to work this winter to snip off all brit cons. and fit modern. Should only take a year or so... :wink:

Click to expand...

Please don't do this. Most people do a piss poor job. More problems are created than solved. Also, there is nothing worse than a classic bike with those pink and blue flat-bladed connectors. The Lucas bullets and connecting sleeves are available and you really need to just replace the multi-wire ones under the tank and in the headlight shell. These are the ones where the metal is usually split inside and in pieces. A heat gun does a good job softening the rubber so the wires come out easier.

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I'm going to tidy up the connectors over the winter and replace connectors with a Lucas type connector or similar. I have clear heat shrink that does a very nice job but it is a little thinner than the heavier clear plastic normally used on a bullet connector.

I'll sort out that can this weekend and load test my battery. I hate to buy one this time of year but I'll ride the bike until the salt comes out.

If you're really interested in a new regulator, check this out. voltage-regulators-t22113-45.html

It may be informational to read the whole thread, but the last page or 2 is the crux of the matter and includes the part number, SH775. More recently, jeans-voltage-regulator-installed-performance-t23449.html

But yes, clean it up first. It may be that some connectors need replacing, but if they're cleanable, put de-ox on them and the grounds can be as important.

First thing to do is replace ALL the female bullet connectors. Because they all look like this and you can't see it. Intermittent high resistance connections.





The replacements are available here:
http://www.britishwiring.com/category-s/266.htm

My wiring harness has been rock solid for 20,000 miles now.

concours said:

First thing to do is replace ALL the female bullet connectors. Because they all look like this and you can't see it. Intermittent high resistance connections.

The replacements are available here:
http://www.britishwiring.com/category-s/266.htm

My wiring harness has been rock solid for 20,000 miles now.

Click to expand...

Great link! Thank you thank you thank you!!!