2MC - how to test them?

Hi all, I got a couple 2MC capacitors ("the blue one") for free, both of which are genuine Lucas products. At least one of them looks to be a replacement. How can I test them to assess their usefulness?

AN sell a replacement which requires a different spring, while Norvil sell a Lucas 2MC cap which fits the original spring - I would like to retain the looks of "the blue one". Before ordering a new cap, I would like to know if my samples are really shot.

Thanks, Knut

Testing instructions are in the electrical section of the manual J24.

mdt-son said:

Hi all, I got a couple 2MC capacitors ("the blue one") for free, both of which are genuine Lucas products. At least one of them looks to be a replacement. How can I test them to assess their usefulness?

AN sell a replacement which requires a different spring, while Norvil sell a Lucas 2MC cap which fits the original spring - I would like to retain the looks of "the blue one". Before ordering a new cap, I would like to know if my samples are really shot.

Thanks, Knut

Click to expand...

Their job it to let you start the bike with a dead battery and the fuse out. This works well with points ignition and may work with an EI on a hill bump start. If this is not you, it would be better to get rid of the extra complexity - just tape off the connectors. Edit: If there are separate Brown/Blue wires in female spade connectors then those wires must be connected together before taping off - recommend cutting off the female spade connectors, soldering the wires together or using good inline connectors and then insulating.

When I build Commandos, I leave them out unless the purchaser insists "for looks" but I never connect them or even run the wires to connect them (I hand wire all bikes). I don't know what "for looks" means when you can't see them anyway!

If you REALLY want one, then https://a.co/d/fZ7arFB fit the spring and are higher capacitance and much more likely to start the bike. I use these on battery ignition singles dirt bikes wired in place of the battery and used install them on Norton's until I realize that there really was no point.

marshg246 said:

it would be better to get rid of the extra complexity - just tape off the connectors.

Click to expand...

If the two brown/blue wires are disconnected from the 2MC then they often have to be connected together otherwise there may be no power reaching the ignition switch.

L.A.B. said:

If the two brown/blue wires are disconnected from the 2MC then they often have to be connected together otherwise there may be no power reaching the ignition switch.

Click to expand...

True if in separate female spade connectors - I should have specified - I have edited.

Many are two wires in a single female spade connector (highly preferred).

If separate all the more reason to get rid of them - two more potential bad connections! Just cut off the spade connectors, join the Brown/Blue wires, and insulate.

marshg246 said:

True if in separate female spade connectors - I should have specified - I have edited.

Many are two wires in a single female spade connector (highly preferred).

Click to expand...

There would normally be a double brown/blue and a single brown/blue that use the 2MC as a connection point, not quite as it's shown on the wiring diagram but having two brown/blue connections. The simplest way to disconnect the 2MC is to remove the earth/ground connector.

L.A.B. said:

There would normally be a double brown/blue and a single brown/blue that use the 2MC as a connection point, not quite as it's shown on the wiring diagram but having two brown/blue connections. The simplest way to disconnect the 2MC is to remove the earth/ground connector.

Click to expand...

Yes, but that still leave two potential bad connections.

I'm helping three people directly right now chasing down poor connections in their bikes. Since the original dummies used the same 14-strand wire for the Red and Brown/Blue wires throughout the bike they, the fuse holder, master switch, and all the connections between are often the root of their problems. I work on real Norton, Triumph and sometimes BSA wiring a LOT over the phone and I rewire quit a few bikes that the owners cannot resolve even with help - I no longer fix wiring on bikes brought to me - much easier to rewire and then I get no call backs.

Often the workshop wiring diagrams do not show connector/connection reality but normally do show electrical reality if unmodified. However, lots of people have at least partly changed the wiring by installing later regulators and correctly or incorrectly removing bridge rectifier and Zeners and some even notice that one of the Brown/Blue wires to the capacitor, if installed, ends up nowhere on most bikes and eliminate it (MK3 different) Those that eliminate the power socket and remove the wire also change the wiring to the capacitor on a MK3 but not on most earlier bikes..

So, yes there can be 1, 2, or 3 Brown/Blue wires to the capacitor and from the factory drawing there are three after (I think 1968). To eliminate the capacitor, the Brown/Blue wires must be connected together whether 2 or 3. To disable the capacitor and leave it in place, disconnect the red, but that still leave two potential poor connections if there are two female spade connectors.

Just a note about the 850 Mk3 as the harness has no Interpol wiring and the ignition switch is up front the extra brown/blue from the 2MC goes to the auxiliary socket. The original harness of my Mk3 I think needed the two 2MC brown/blues connected together but the replacement harness did not if I remember correctly however I still have the 2MC connected.