R8249 decoder in R2951 DVT lighting problem

[NigC]

So, I have the Hornby R2951 Wrexham & Shropshire pack (class 67 plus DVT).

I have put a Hornby R8249 decoder in the DVT, which is correctly showing red lights at rear when going forwards. However, when going backwards the white headlights do not come on as one would hope, but instead an internal cab light comes on. I’m thinking I need to change some CV’s but not sure where to start (I’m still new to DCC). Alternatively is the circuit board in the DVT wired wrongly ? Any help or suggestions welcomed. Thanks in advance.

[Fishmanoz]

Hi Nig, fixing this with CVs would need what is known as function mapping and the 8249 does not have this capability, no Hornby decoder does.

It’s almost certainly a wiring fault with the decoder yellow function wire connected to the cabin light instead of the rear headlight.

In this loco, is it supposed to have a working cabin light? If so, try the function to turn it on and see if it switches on the rear headlight?

Someone will be along soon who knows specifics of this loco and will be able to tell you which wires to move where.

PS. Mods, could you please add to Nig’s title “ … causing cabin light to come on instead of rear headlight in reverse”. With the title showing the specific problem, he will be more likely to attract those in the know on this.

Mod note - tried to amend the title but keep getting an error, so maybe there is a character count limit in the title field. Eventually got it to change partially as can be seen, which will help future searches.

[96RAF]

Does the rear headlight show if you select F1, which would indicate a miss wire of the green and white or yellow wire. Or could it be the rear headlight light tube (or whatever) is misplaced and is working but lighting up the cab rather than the headlights

[NigC]

Thank you very much Gentlemen.

As suggested by 96RAF it was matter of the light tube for the headlight being slightly displaced. Tricky little blighter to get back together, but it’s done and all working as it should.

Thanks again for your help.