Brake light always on

[Deleted User 62]

Thanks Rob and everyone else, note: the original front brake switch on a 1974 was on the perch, like a /5. The owner has bypassed the stock wiring somehow and gotten it working.

[Rob Frankham]

Thanks Rob and everyone else, note: the original front brake switch on a 1974 was on the perch, like a /5. The owner has bypassed the stock wiring somehow and gotten it working.

Hi Tim,

You may well have a point... but...

If the bike has the later type levers, then it's either a late '74 (i.e. '75 model) bike or the levers/circuitry have been modified (in which case, all bets are off and you need to go back to basic 'cause who knows what was done. In the absence of wires to the handlebar perch, I would still want to look to see if there's a pressure switch under the tank.

Rob

[jagarra]

Airbear, providing a schematic helped clear the issue of whether diodes were part of the problem. But on your comment about having continuity in both directions when reading a diode is incorrect. Diodes shoulld only really show a low reading on continuity in one direction, when the leads of the meter are reversed and then applied to the same points you should expect a much higher reading, 100 times or more a greater value. They are designed to conduct in one direction, sort of like a check valve. If you saw a reading in both directions close to the same value, the junction may be bad, I would unsolder one end, lift it and recheck it if that occured. If the same, it's bad.

regards,

gg

[Deleted User 62]

Thanks Rob and everyone else, note: the original front brake switch on a 1974 was on the perch, like a /5. The owner has bypassed the stock wiring somehow and gotten it working.

Hi Tim,

You may well have a point... but...

If the bike has the later type levers, then it's either a late '74 (i.e. '75 model) bike or the levers/circuitry have been modified (in which case, all bets are off and you need to go back to basic 'cause who knows what was done. In the absence of wires to the handlebar perch, I would still want to look to see if there's a pressure switch under the tank.

Rob

Hello Rob, this bike was bought as a pile of parts including /7 perches, a cut and hacked RT wiring harness and mismatched relays. There is a pressure switch on the MC and you were right, that's where the always on power to the brake light was coming from. We switched back to a '74 main wiring harness and relays, which got the instrument lights and starter working, but because the connecter board in the headlight is from a later model bike, there are no place for some of the wires from the switches to go (missing any green with black or red stripe connectors). Now that he knows he can use the brake light switch on the MC, he wants to retrofit it back to the original type handlebar switches and perches. Fortunately I have most of that stuff in used stock, but after fighting the electrical issues for two weeks, he just wants to ride the bike the way it is for now. Can't say as I blame him. It's been a long, strange trip so far...

[Airbear]

Airbear, providing a schematic helped clear the issue of whether diodes were part of the problem. But on your comment about having continuity in both directions when reading a diode is incorrect. Diodes shoulld only really show a low reading on continuity in one direction, when the leads of the meter are reversed and then applied to the same points you should expect a much higher reading, 100 times or more a greater value. They are designed to conduct in one direction, sort of like a check valve. If you saw a reading in both directions close to the same value, the junction may be bad, I would unsolder one end, lift it and recheck it if that occured. If the same, it's bad.

regards,

gg

gg, yep, knew that and figured it went without saying, but a good point to clarify. Cheers.