1974 ST 90 Lights not working

[rippinmachines]

I've gone through the wiring in the headlight bucket and cleaned connections with contact cleaner.

Any ideas?

Horn beeps but no lights and bulbs look good.

 

[b52bombardier1]

Get a multimeter and set it to DC volts. And start tracing backwards from each bulb to find six volt power. Probably a bad ground since both are affected. Or possibly a broken wire in the headlight switch. These bullet connectors can look good but be bad inside the insulation.

With a good multimeter or test lamp with a wiring diagram, finding the fault should be easy.

Rick

 

[rippinmachines]

So turn the key on and open the bullet connectors for the headlamp and insert a test light?
Does the st90 need to be running to have the lights on?
Isn’t there just one ground to the frame under the battery box?

 

[b52bombardier1]

Hello,

Yes, to your connection for the test light but there may be a wire break inside the insulation. Neither the CT90 or ST90 require the engine to be running. If you have a healthy well charged battery, they will illuminate with merely the key on and the headlight switch to low or high.

Take a look at an ST90 wiring diagram. Lotsa' grounds, not just one. I have had to supplement my rear turn signal grounds because of poor contacts there through the turn signal stalk. You can't have too many grounds on these bikes.

Rick

 

[rippinmachines]

Thanks, Rick.

I've clean up a bunch of bullet connectors in the headlight bucket and at the rear of the bike. I also had the engine out to replace the ignition coil/condenser and and am wondering if my problem lies at the main wiring harness.

I have a multimeter and a test light. What would be the step by step way of sorting this out?

I find the wiring diagram difficult since it isn't broken down by each are of the bike ( frame, headlight bucket etc.)

 

[joel1234567]

I'd start with a continuity check on the bulb to verify if the filament is shot or not. There's prob like a white wire, blue wire, green wire? Set meter to ohms to check continuity, touch the probes together to verify it beeps (or does whatever you meter does). Then try probes on white and green wires, then blue and green wires. One is low beam, the other is high beam. If there's no beeping the bulb is shot.

 

[rippinmachines]

I'd start with a continuity check on the bulb to verify if the filament is shot or not. There's prob like a white wire, blue wire, green wire? Set meter to ohms to check continuity, touch the probes together to verify it beeps (or does whatever you meter does). Then try probes on white and green wires, then blue and green wires. One is low beam, the other is high beam. If there's no beeping the bulb is shot.

After the test i've determined the Front headlight is no good and there was a 12v bulb in the tail light which i switched out to a 6v and it works well now.

Turn signals also had 12v bulbs in them which I switched to 6v but they don't light up. Any obvious things to look for in regards to the signals?

 

[b52bombardier1]

Add a temporary, supplemental ground wire from the negative battery wire to the metal base of the turn signal. If your turn signal works with this temporary ground, you know which half of the circuit has failed. Fix that.

Rick

 

[joel1234567]

The old 6V blinkers suck a lot of juice and are also very dependent on you having the correct wattage bulbs in your blinkers before they activate. A good test is to test them while revving up the bike as sometimes they might not even activate at idle or with a low battery. Or with the wrong bulbs, not at all. The old winker relays heat up as wattage to the bulbs passes thru them and it bends a bi-metallic strip like an old thermostat. Wrong wattage bulbs, not enough heat, not enough bend. You can switch to a digital winker relay instead but I haven't seen good ones around recently for 6V systems. DrATV used to have one but they've been sold out for a bit. They're less sensitive to the bulb wattage and less drain on the battery.