Electrical System
- Thread starter Julesbase
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Nothing magical about any "ground"; "positive ground" just means the harness Red wires and some metal bits of the bike conduct the electricity from components to the battery +ve terminal.
The common electronic ignitions for these bikes, none of their components "ground" through their mountings so none of them have any electrical contact with anything but the bike's harness wires, meaning the e.i. component wires simply have to be connected to the bike's harness correctly and the e.i. should work.
76 Triumph did not have electronic ignition as standard, it has been fitted by a previous owner since the bike left the factory; "amplifier" suggests you have a Lucas Rita e.i.; please post confirmation or the make and model of the e.i., or photos of the components, I can advise how to connect it to the bike's harness.
Rudie, Thanks so much for your input. After a little research I found out that my that my late brother’s bike did have an electronic ignition upgrade. I’m not sure what unit was used to replace the points but It has the Lucas Rita Ab11 amplifier. These units are still wired to the bike. I have some damaged wiring to repair, I will keep you posted on my progress. Thanks again and Happy and healthy New Year.
While Lucas developed the AB11 primarily for US 79 T140E so the engines could meet the lower 1979 emissions limits mandated by the EPA, Mistral Engineering - a small British company - had been handling Rita motorcycle sales and servicing for Lucas since the early 1970's. Company founder John Carpenter had designed a unit to replace the points and auto advance unit in the timing cover, that triggered the earlier AB5 amplifier (originally developed for cars) mounted elsewhere on the bike.
It is not impossible someone fitted your bike with an AB11 and 5PU trigger unit from a 79 or later twin; however, more likely is your bike has an AB11 supplied by Mistral with John's (more reliable) trigger unit;
if you post a photo of the insides of the original points cavity in the timing cover, I can tell you what has been used to replace the points on your bike.When connecting specifically an AB11 to a British bike with earlier 'positive ground' electrics - such as your bike - some things to know:-
. Because the 79 Triumphs the AB11 was designed for also had 'negative ground' electrics, the AB11's wire colours are coded for the latter.
. So NEVER connect the AB11 White/Yellow wire to a pre 79 Triumph's White/Yellow wire from the kill switch. Connect the AB11's Black wire to a pre 79 Triumph's White/Yellow wire.
. Pre 79 Triumph, in theory you can connect the AB11 White/Yellow wire to any random part of the bike that should be 'ground'. In practice, John advised connecting AB11 White/Yellow directly to the battery positive terminal.
. What ignition coils does your bike have?
.. Two separate ignition coils - both marked "6V" and having a primary resistance between 1.5 and 2.2 Ohms - the AB11's White/Black wire should be connected to only one coil's negative terminal, that coil's positive terminal should be connected by a wire to the other coil's negative terminal, only that second coil's positive terminal should be connected to a harness Red wire on the bike; again, John recommended against connecting the second coil's positive terminal just to some random part of the bike.
.. Otoh, a single coil with dual HT leads should be "12V" and have a primary resistance between 3 and 4.4 Ohms; the AB11's White/Black wire should be connected to the coil's negative terminal or wire, the coil's positive terminal or wire should be connected to a harness Red wire.
. AB11's White/Orange and White/Purple wires, I could do with seeing a photo of your bike's trigger unit before advising how it and the AB11 should be connected together.
. The AB11 should have a sixth wire connected between one of its mounting bolts and the battery positive terminal. This is most important as the amp protects the electronics from external Voltage spikes using the metal casing; if the casing is not connected directly to the battery positive terminal, the spike protection does not work.
Finally here, if one not fitted already, consider fitting a low Amps fuse in the Rita supply, because the standard single 35A (blow, 17.5A continuous) fuse near the battery is rated much too high to protect just the Rita amp. I fit a 5A fuse in a modern blade fuse holder where the bike's White/Yellow wire connects to the AB11's Black wire.
However, re-reading my previous post, I realise I have assumed your bike still has standard pre 79 'positive ground' electrics but have not advised checking this.
Thank you.I am still in the process of unraveling the wire harnesses. I will check on the polarity. Getting back to the amplifier and the electronic ignition. These components are wired into the bike. I will re-check the connections with the information you provided. I have another question if you don’t mind, I bought two new coils they are 12 V. Would these be OK some people say to 6 V is the way to go my thinking 12 V system 12 V coils. Please advise. Have a great day.
The harness itself might not tell you correctly, especially if it was not connected to a battery when you got the bike. Standard 76 (any pre 79) harness has a Brown/Blue wire (insulation mainly Brown with one or two thin Blue stripes) connected to battery negative, one or more Red 'ground' wires connected to battery positive. Problem is it is easily possible to connect those wires to the opposite battery terminals (to "convert to negative ground"
).However, what stops "converting" being that simple are the standard rectifier and Zener diode, because they both 'ground' through their mountings and contain diodes; as a rule, diodes only control current (Amps) in one direction; connect 'em the wrong way round, short circuit, fuse blows.
What can tell you correctly the 'ground' of the bike's electrics are the rectifier (as standard, mounted between the coils behind the battery, marked "STUD +") and Zener diode (as standard, mounted on one of the airboxes, marked "+").
However ...,
a regular mod on these bikes it to replace both rectifier and Zener with a combined regulator/rectifier ... If the wires from the alternator stator (thick black insulated cable out of the primary casing under the carbs above the gearbox casing) are connected to Yellow wires and those run to a finned "box", that is an aftermarket reg/rec. Post if your bike does have that and I will post what to look for to check 'ground'.Not with an electronic ignition like the Rita.
Are you sitting comfortably ...?
Two things:-
1. "12V" on a battery and "12V" on a coil mean two different things:-
. "12V" on a battery means its nominal potential difference (unit "Volt") between its negative and positive terminals.
. Otoh, "12V" on an ignition coil (or a bulb, horn, etc.) is only a rating; coil, the "Volts" are shorthand for the coil's primary resistance (unit "Ohm"). Specifically a coil switched by points, it is most desirable its primary draws between 3 and 4 Amps (current) when the rated Volts are applied across the primary terminals. What controls the Amps drawn by a component is its resistance:-
.. the link between Volts, Amps and Ohms is the formula "Ohm's Law" - Volts equals Amps multiplied by Ohms.
2. Correct if switched by points, not if switched by an electronic ignition.
Most e.i. for these bikes were intended only to replace the points (and auto advance unit) so essentially they will work with coils intended for switching by points. However, the fundamental difference between switching by points and switching by e.i. is:-
. Switched by points, multiple coils are connected between battery negative and battery positive "in parallel", meaning each coil has its own feed from battery negative, its positive is connected to its points, its points 'ground' - connect it to battery positive - when closed.
. Otoh (due to history), all electronic ignitions for old Triumphs are basically similar to your bike's Rita, in that they all have just one switched output (on your bike, the Rita's White/Black wire); multiple coils must be connected between battery negative and battery positive - to the e.i. single switched output - "in series":-
... i.e. on a twin:-
.. the second coil in the series is fed from battery negative and the switch (Rita amp on your bike) through the first coil;
.. the first coil in the series 'grounds' to battery positive through the second coil.
Then the easiest (if incomplete) way to understand why two ignition coils connected "in series" should be "6V" each even when the bike's electrical system is 12V is: the Volts between the battery's negative and positive terminals, across the "series" are 'shared' between the components in the series - i.e. nominal 12V between the battery's negative and positive terminals, two coils connected in series, each coil's 'share' is 6V:-
...
Otoh, if two "12V" coils are connected "in series" to the Rita's switched output, each coil's 'share' is still '6V' ...
:-. Further up the post, I mentioned, ""12V" on an ignition coil (or a bulb, horn, etc.) is only a rating; coil, the "Volts" are shorthand for the coil's primary resistance (Ohms). Specifically a coil switched by points, it is most desirable its primary draws between 3 and 4 Amps ... when the rated Volts are applied across the primary terminals":-
... if only 6V is applied across a "12V" coil's primary terminals, the previously mentioned Ohm's Law says the coil will only draw between 2 and 1.4 Amps respectively.
. While cutting Amps draw looks good in theory,
in the case of ignition coils. Ignition coils are transformers - their secondary (HT) windings are charged by the magnetic strength of the primary windings, generated by the Amps passing through them. If the Amps passing through the primary windings are reduced, their magnetic strength is reduced, they take longer to charge the HT windings, the HT windings can generate a weaker spark, can fail to generate any spark at all. 
... on a twin, including Lucas who made the Rita e.i. on your bike.
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Great tutorial, Rudie 
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