Vintage Cars: MGTD turn indicators, bmc cars, dashboard switch

Question
The turn indicators on front and back work when the turn indicator switch is operated, but the repeater lamp on the dashboard only comes on once then stays off. The is the same whether using left or right indicators. Should I replace the Flasher unit or is the relay box at fault??

Answer
The TD is really outside my ken, and faulty British electrics can drive you nuts, but I think the arrangement is common to later BMC cars, so I'll try.

First suspect connections... Take the repeater bulb out, clean the socket, check that its wire connection is good, make sure the socket is grounded properly to the dash, and replace. Also check connections to the relay box and flasher unit. Most electric problems in old cars are caused by bad grounds or bad wire connections, especially unsoldered bullet and spade connectors (crimps are really not reliable). But if no clear cause along those lines...

The fact that the flashers work (I'm assuming the frequency is about normal, not fast) tells me the flasher unit is OK: all it has to do is switch a connection on and off. What is odd is that your repeater lamp is not apparently getting the same signal that the lamps are.

The relay system overrides the brake switch when flasher and brakes are on together and it enables having a single bulb for both flasher and brake at the rear. It's quite complex, but it doesn't have to know whether it's going to left or right. The flasher unit doesn't have to know either. And neither does the repeater bulb (I assume it's a single repeater on the dash, not one each way.) Think of the dashboard switch as the last thing in the circuit, which distributes power left or right accordingly.

Ergo, I think the relay or the relay connection is suspect, but I can't tell you exactly because I can't find a wiring diagram on the web to tell me how the repeater should be connected to it. If it worked before and then went bad, and if the flash frequency is OK, I would consider replacing the relay; I think electronic replacements are available.

Sorry not be more help. If you can find a wiring diagram on the web, post again with the url and I can probably help more.

JJ