Electrical gremlins

[TR5convalescent]

Afternoon all. I spent some of the winter down time getting the radio cassette working and replacing the dash lighting with LED bulbs. I now discover that, while I have successfully by passed the pointless instrument dimmer and now have beautifully lit instruments in a fetching shade of blue, as soon as I turn on the ignition the speedometer light (and only this one) goes out. The previous owner had a bridge in the red white wire to the bulb holder (earth being provided by the star clip biting on the speedo body as with the Rev counter). I have run a feed straight off the wires which by pass the rheostat and a supplementary earth direct to the bulb holder body and yet as soon as the ignition is switched on the speedo light goes out and won't switch on again until the engine is stopped and the key returned to the insert position.

Any thoughts on how to isolate the fault?

[StagJonno]

Afternoon all. I spent some of the winter down time getting the radio cassette working and replacing the dash lighting with LED bulbs. I now discover that, while I have successfully by passed the pointless instrument dimmer and now have beautifully lit instruments in a fetching shade of blue, as soon as I turn on the ignition the speedometer light (and only this one) goes out. The previous owner had a bridge in the red white wire to the bulb holder (earth being provided by the star clip biting on the speedo body as with the Rev counter). I have run a feed straight off the wires which by pass the rheostat and a supplementary earth direct to the bulb holder body and yet as soon as the ignition is switched on the speedo light goes out and won't switch on again until the engine is stopped and the key returned to the insert position.

Any thoughts on how to isolate the fault?

Very puzzling. I'd try swapping out with one of the other bulbs which are showing normally. Just a chance that that bulb is responding to some interference from your ignition circuits. Don't call me barmy until you've tried this

Jonno

[pagan]

Could it be the polarity of that LED ?

[V Mad]

This can happen if the speedo case is not properly earthed. Try putting an extra earth on the speedometer case.

[TR5convalescent]

Useful suggestions, both. Unfortunately, I am on painting fatigues this weekend, so I will give it a go next week sometime.

Thank you, gentlemen.

[TR5convalescent]

Hi chaps. Finished early so as I was out in the garage cleaning brushes anyway, I ran a temporary lead from the speedo body to earth and the speedo light worked with ignition on.

So thanks to you both, but especially Chris. I haven't time to make a permanent fix right now as I have to do a set list for tonight's gig and then load up, but I will get it done in the next few days.

[StagJonno]

Hi chaps. Finished early so as I was out in the garage cleaning brushes anyway, I ran a temporary lead from the speedo body to earth and the speedo light worked with ignition on.

So thanks to you both, but especially Chris. I haven't time to make a permanent fix right now as I have to do a set list for tonight's gig and then load up, but I will get it done in the next few days.

Glad you're sorted.

[Pete]

Hi chaps. Finished early so as I was out in the garage cleaning brushes anyway, I ran a temporary lead from the speedo body to earth and the speedo light worked with ignition on.

So thanks to you both, but especially Chris. I haven't time to make a permanent fix right now as I have to do a set list for tonight's gig and then load up, but I will get it done in the next few days.

Where you playing?

[TR5convalescent]

Pete, I'm really sorry. I closed my iPad at 1610 yesterday, fell asleep till 1700 and then ran around like headless chicken for a while before driving to the bass players house to load.

We played at the King George on London Road in Wycombe - to an audience that nearly outnumbered the band!

We're on FB under our name NNU. We play around Bucks, Berks and Herts with an occasional foray into Oxon.