Hello, just bought a '89 740 GL

[Laird Scooby]

Originally Posted by ton246

According to the receipt, the tow bar was installed in 1992, not that should make any difference. I think when i've nothing else better to spend my money on, I was going to get the electrics rewired for the tow bar.

That sounds like a good idea! Does the bulb failure unit still work at the moment?

[ton246]

Originally Posted by Laird Scooby

That sounds like a good idea! Does the bulb failure unit still work at the moment?

Yes, 'cause when i fitted the drivers side rear light, the brake light wasn't working which showed up on the dashboard. Now sorted tho.

[Laird Scooby]

Could well be they have fitted relay to power the trailer lights separately in that case. Can't think of the most common brand at the moment but Transflash rings a bell. Basically instead of doing it the traditional way of using the vehicles flasher relay for the indicators and taking the power from the rear lights for the lighting feeds, it has a feed from the battery then uses the feeds to the rear lighting to operate relays in the unit to power the trailer lights.
This saves time and labour charges by not having to strip out half the dash to get at all the various cables for the lighting but obviously costs more for the unit.

If all is working then i would suggest "if it ain't broke, don't fix it" unless there are some obvious wiring problems with it.
I know i said earlier it might be a good idea to get the trailer wiring rewired on the car but that was before i remembered those units. You should be able to find it fairly easily, tucked in the back somewhere. Maybe the receipt will give a clue if it lists what was fitted?