BN1 - Electrical gremlin...

[Michael Oritt]

Matt--

In your last you said "I'll make a specific new wiring, just in case..."

Since you cannot seem to replicate the condition except when on the road I was going to suggest that at least until you can isolate the problem you--successively if necessary--create a dedicated and separately fused circuit for each of the wires to see which one blows while you are doing test drives.

As I said earlier sometimes it is just easier to rip everything out and start from fresh but your desire to find and solve the problem is admirable. Stick with it and sooner or later it will show its ugly self!

 

[matt78]

Matt--

In your last you said "I'll make a specific new wiring, just in case..."

Since you cannot seem to replicate the condition except when on the road I was going to suggest that at least until you can isolate the problem you--successively if necessary--create a dedicated and separately fused circuit for each of the wires to see which one blows while you are doing test drives.

As I said earlier sometimes it is just easier to rip everything out and start from fresh but your desire to find and solve the problem is admirable. Stick with it and sooner or later it will show its ugly self!

Thank you for your encouragement (I hate being stuck w/o understanding the trick!).
Regarding the "rip everything out", I think that having already replaced the gearbox switch, the OD complete harness and the 2 relays, I'm not so far...

In addition to all what I had already done, today I decided to shunt the throttle and the centrifugal switches : as you'll imagine (business as usual), the result was unchanged - a blown fuse...

The last elements still to be checked were :
1) the OD fascia swtich (but as it grounds the contact, it seems difficult for it to create a short...) and
2) the gearbox switch. This one being always connected to the live 12 V, it could be the origin of my problem. I had previously thought of shunting it, but as it's a BRAND NEW ONE, I didn't pay attention no more...
So, I disconnected it, and * BINGO *, no more blown fuse !
I reconnected all the circuits, and everything is ok, except, of course, the lack of 'box switch in case of a 1st gear or, far more dangerous, reverse activation. But the centrifugal switch will help avoiding such a disaster, even if in some situations, it might still be useless.

So, the main lesson here is : do NOT always trust a new part (esp. for electrics), because it might be faulty, too !
I learned it the hard way...

Thank you guys for all your messages, it's good to get some support in such a case, and always useful to learn from experienced people ! Unfortunately, I can't really help others...

See you soon (many other things to do, so many questions to ask ).

Matt

 

[pan]

I have had problems with replacement top gear switches. I think it is because the type now available is suited to the later transmission where the switch is high up, just below the gear change lever, and thus above the oil level. On a BN1, the switch is exposed to the oil. I have found that removing the switch and washing it has made it function again.

 

[matt78]

YES ! That's it !
I remember having opened the previous faulty switch (which didn't seem to be that old...), in order to understand what happened, and found some oil inside.
I couldn't imagine that my new (Lucas original) switch might NOT be sealed, thus causing the same kind of failure.
Of course, the vendor didn't knew that - nor many other things, as I discovered recently :grief:

Thank you for this very interesting information, useful for my global understanding.

Matt

 

[pan]

Matt,
I am glad I was able to help, but when I have had the top gear switch fail due to contamination with oil, my overdrive has simply failed to engage or dropped back to direct drive. I have never had a fuse blow.