Any Electrics Experts

[Pete D]

Hi All

I wonder if a chap far wiser than me can help on a 1976 900A4 electrical problem:

I noticed that the idiot lights dimmed whenever I selected run on the right switchgear. Further, the neutral light gets brighter after engine start with higher revs (despite a new replacement regulator/rectifier just fitted). On closer checking, the voltage when run selected (checked on the connections to the switch) drops to 10V, but is 12.2V when stop selected. I have also checked the wiring downstream. When the coils are unplugged from the harness, I get 12.2V on the harness bullet connector point; the voltage also remains at 12.2 at the coil positive terminals when I disconnect the coil earth wires. If I connect the coil earths, the voltage drops to 10 again. Lastly, if I connect one coil at a time, the voltage still drops to 10 with either connected. Is this normal behaviour, or if not, has anyone an idea on how I can rectify?

Although I enjoy fettling, this has me stumped......and the headlight reflects the varying voltage with revs.....so the system is being dragged down somewhere....

If it helps with the diagnostics, the bike is fitted with electronic ignition (by previous owner).

Cheers

Pete

[Gray17]

Reading your post their are several possibilities.
Firstly assume your turning the ignition on and watching the idiot lights on battery only, when you turn cut off to run they dim, thats normal as your adding extra load of the coils onto the circuit. You say the voltage drops to 10v, is this at the coils or across the battery itself? You also mention the headlight dimming are all these being run without the engine running?
If its the battery then sounds like you need a replacement as it should maintain at least 12v for a period before dropping down, if its at the coils, but the battery remains at 12v then you have issues within the loom itself, possibly loose or corroded bullet connectors or faulty wiring and it will need checking.
Also what is the voltage across the battery itself when the engines running it should be 13.8v but may be slightly higher or lower depending on load. If its a lot higher then maybe the rectifier or regulator are not working correctly. When it was replaced, was the battery replaced at same time as it may well have been damaged.
Personally i would start by measuring the battery with 1 terminal disconnected and find its quiescent state. It should be at least 12v if not try charging it overnight on a smart charger, or replace it.
Next re fit it to bike and start bike, no headlights on, again measure the voltage at the battery see if its now sitting at 13.8v or thereabouts, then turn on headlight, again check voltage should still be at around the 13v mark if a lot lower, you have a charging issue, perhaps alternator, weak magnets are a possibility or faulty phase coils.
Suggest get yourself a good wiring diagram and check all of the connections for corrosion etc, it maybe time to replace the loom itself as at 40 years old they dont last forever. Same applies to batteries.
Good luck hope the pointers help

[zed1015]

As above.
The lights brightening when running shows the generator is producing current and the new reg/rec should rule out those components
The headlight dimming and brightening slightly with revs is not abnormal but if very noticable especially affecting the idiot lights etc indicates either a poor battery/earth connection or that the battery is unable to hold a full charge and on it's way out.

[Pete D]

Thanks. I’m going to try the direct feed to coils via relay mod first, and invest in a new battery (one was fitted last year, but potentially goosed by the duff T/R setup).

[Pete D]

Reading your post their are several possibilities.
Firstly assume your turning the ignition on and watching the idiot lights on battery only, when you turn cut off to run they dim, thats normal as your adding extra load of the coils onto the circuit. You say the voltage drops to 10v, is this at the coils or across the battery itself? You also mention the headlight dimming are all these being run without the engine running?
If its the battery then sounds like you need a replacement as it should maintain at least 12v for a period before dropping down, if its at the coils, but the battery remains at 12v then you have issues within the loom itself, possibly loose or corroded bullet connectors or faulty wiring and it will need checking.
Also what is the voltage across the battery itself when the engines running it should be 13.8v but may be slightly higher or lower depending on load. If its a lot higher then maybe the rectifier or regulator are not working correctly. When it was replaced, was the battery replaced at same time as it may well have been damaged.
Personally i would start by measuring the battery with 1 terminal disconnected and find its quiescent state. It should be at least 12v if not try charging it overnight on a smart charger, or replace it.
Next re fit it to bike and start bike, no headlights on, again measure the voltage at the battery see if its now sitting at 13.8v or thereabouts, then turn on headlight, again check voltage should still be at around the 13v mark if a lot lower, you have a charging issue, perhaps alternator, weak magnets are a possibility or faulty phase coils.
Suggest get yourself a good wiring diagram and check all of the connections for corrosion etc, it maybe time to replace the loom itself as at 40 years old they dont last forever. Same applies to batteries.
Good luck hope the pointers help

Hugely helpful; thanks very much. I have traced most of the wiring to check continuity etc, and cleaned a fair few of the connectors. Nevertheless, I think, over the 40 years, that one or more of its previous owners has 'modified' the harness somewhat, particularly as I have yet to find a diagram that matches the wiring colours exactly....! However, everything else works, so I am somewhat reticent to change the harness in toto (though I have recently fitted a reg/rectifier - the old units were cooking the battery.

Post reg/rect fitting the voltage acrss the battery with engine running is within spec.

In the meantime, I'm going to supply the coils direct from battery via a relay (switched by the run/stop switch) as I think that a worthwhile mod to ensure a strong spark. The Dyna S electronic ignition has a reputation for heavy system load draw, and such a direct connection will mitigate harness weaknesses. I'll report back with results re low rpm running etc afterwards.

[Pete D]

Hi All

Having modified the loom to feed the coils direct from battery via a relay, and having replaced a coil that had a dodgy positive terminal, my problems of rough running seem to be cured.

Here's hoping......but awaiting the next minor snag to raise its head soon - the joys of running classic vehicles!

[r3sc]

Pleased your modification has worked out.

I’m not a huge fan of the relay modification to power the coils as it has some inherent issues.

If I were to do this mod I would use a relay with positive break contacts which means that if the contacts weld together, when the power is removed from the relay coil, the contacts will physically break open even at the cost of damaging itself internally.

This type of relay is used in safety critical applications and is signified by a circle with a small arrow in it.

They’re not expensive, certainly cheaper than a new set of coils.

[Pete D]

Very wise words, and easy for me to swap in; thanks.

Just come back from first shakedown ride. Happy to report smooth running throughout the rev range, no smell of electrical components heating unduly, and loom routing remains away from any hot engine parts.

All in all, a fairly happy bunny. Just a few tweaks to refine carburation. At least the Zed is considerably better designed than my old Hesketh; that really was an electrical and fuel system nightmare!

[r3sc]

Hi Pete D,

I also used to ride a Hesketh.

I liked the bike but it was too tall and every time you sat on it while it was on the side stand it would try to throw you off the other side.

Nice looking bike but not very user friendly!

Pleased your Z is running well!

[Pete D]

Here’s my old one:

[Barnett]

Pleased your modification has worked out.

I’m not a huge fan of the relay modification to power the coils as it has some inherent issues.

If I were to do this mod I would use a relay with positive break contacts which means that if the contacts weld together, when the power is removed from the relay coil, the contacts will physically break open even at the cost of damaging itself internally.

This type of relay is used in safety critical applications and is signified by a circle with a small arrow in it.

They’re not expensive, certainly cheaper than a new set of coils.

Thats an excellent point, never thought of that scenario or indeed that forced break relays were available! something learned today, thanks!