Triumphrat

internet ay · 07-26-2008

I noticed tonight that my headlight was dim and when i hit the brake the headlight dims alot. Like a lot more than usual, also when i come to stop signs the head light gets so dim that you can barely tell that the headlight is on and the bike comes extremely close to stalling.

Tested the battery, its fine. What else could it be? Bike is a '72 T120 Bonneville.

Thanks in advance.

Matt

Red1959 · 07-27-2008

What model do you have? What do you have for the lighting/ charging system on your bike?

OzBloke · 07-27-2008

Also, when you say you tested the battery, what tests did you do, and what were the results?

Start looking at the bullet connectors between Alternator and rectifier, connections around rectifier, fuse and battery, and between battery and ignition switch.

Tbirdnz · 07-27-2008

How did you test the battery, thru a load-tester ?

Even bad batteries will show 12v with a AVO meter, I would also check to see you're getting around 14v when the bike is running.
It will prove if your alternator is charging the battery.

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Ride on !

internet ay · 07-27-2008

Bike is a '72 T-120 Bonneville, everything is stock including points setup.

I did the battery load test on the Gamba website, http://http://www.gabma.us/elec/battery_testing.pdf. The results were around a 12v reading after the headlight was on for 2min.

It looks like this could be a loose connection, bad ground problem? Ill start checking all the connections.

internet ay · 07-27-2008

I forgot to mention that the headlight also dims significantly when the turn signal is on also.

Medic09 · 07-27-2008

Did you test to see that the battery is actually charging? On most old bikes, the battery doesn't charge at idle. I don't know exactly about your Bonnie, but in general you need to have the motor up to running revs (on my old Honda above 3000 minimum, better at 4000) to see it charge. At that point a meter attached to your battery should show a 12v battery charging at 14+ volts. Someone will correct me here if it is significantly different for our old Brit bikes.

Also, is the battery properly maintained? If it is a regular battery, is the electrolyte up to level? Has it been sitting a long time without being charged? If the lytes are low, or it has sat and sulfated a long time without charging, it may not be holding a charge even if your bike's charging system is fine. If it is a glass mat battery, it also may not have tolerated a long sit without charging. I tossed one recently on my old Honda because I let it sit too long.

internet ay · 07-27-2008

I am going to have to see if it is charging above 3000 rpms. Also the battery is about 2 months old.

panda · 07-27-2008

sadly from your symptoms there could be many causes.
Check battery voltage (on the battery terminals) with engine stopped, should be over 12v.
check same with motor at about 3k revs, should be climbing towards 13V
If this passes battery and charging components are probably ok.
Now check for clean connections on battery terminals and the alternator output connectors.
make sure the battery to frame ground is good.

failing this it is a hunt through the wiring checking all connections are good. sometimes the bad connection will feel warm..

I recently had an easy one to find on my BMW. The cable from the battery to the starter motor had chafed and shorted out killing the 1 year old 28 amp hour battery in seconds. Fortunately the charging circuit ( a weak point on bmw's) survived.

Panheahpollock · 08-01-2008

I would start with the bucket and check all grounds. Sounds as if there is something that is not allowing the headlight to have a good ground to the chassis and it is actually grounding out through the other light assemblies. Just a thought.