Dimdip Causing a Problem? Newbie

[Piratepete]

Hi Guys
Cybil has just sailed through her MOT. But tester say I need to fix a problem with the sidelights.

Simply, with ignition on, sidelights on, I have full diplights as well. He thought it was a switch problem.

However the switch checks out fine, but is the 9 pin one with a 56D connection - so I probably have dim-dip - very well explained in the Tech Archive.
1. My Current flow Diagram sheet 75/9 dated 07/89 doesn't show the dimdip circuit. So does anyone have a copy I may download, please?
2. It's possible the dim dip resistor has gone short circuit. I understand I can simply remove it. Where is it situated? If it's on the relay/fuse panel, what's it's ID, please?

Cheers!
Pete   1990 T25 2.1DJ Petrol

Hi Guys
Since posting this I've found a circuit diagram on synchrosport.com and a post in Tech Archive says the resistor is behind the right headlamp. So when Storm Francis has passed by, I'll be out with the screwdriver!
Thanks for looking.

[syncroandy]

Sounds like you're onto it. Popping the 56D terminal out of the switch plug would achieve the same as unplugging the dropper resistor.

Link to diagrams: http://syncrosport.com/info/wiring

Another possibility is if you've added headlight relays. In the 'simple' way of doing this, the dimdip current can cause the relay to trigger causing the dipped filament to come on with full brightness. This is one of the reasons I encourage folk to do relays the 'nice' way, and insert them into the circuit before the fuseboard.

I like dimdip, it was introduced back in more civilised times, to provide better safety in low light conditions, *without* causing undue dazzling to other road users.

[Piratepete]

Hi Andy
Thaks for your reply
I feel sure that there are no additional relays based on vehicle history and dim headlights. Where would they be?
I also like the idea of dimdip so don't want to make a permanent disconnection.
I'm assuming it's easy to temporarily pop the 56D connection out of the plug?
Pete

[syncroandy]

Just a thought.. is it possible the tester is being dozy and getting confused by the dim-dip ? Possibly they don't often see vehicles old enough to be aware of it?? I'd be verifying the issue myself before starting do stuff to fix it.

[bigherb]

That is how the Dim Dip system worked, it wasn't so sophisticated as some that only came on when the engine is running. The head lamps should get noticeable brighter when you switch them on.

[Piratepete]

Thanks for all your interest.
There's absolutely no doubt that the dip lights are just as bright in the sidelight switch position as in the the headlamp position. Just rechecked. Disconnecting the resistor solves the problem (no dimdip at all). Resistance is 0.99 ohms. Anyone know what it should be?

Andy, you were musing whether headlamp relays had been fitted, causing the problem. I've got numbered relays in locations 4,5,8,10,11, and 12. These are numbered respectively 42, 53, 18, 19, 72 and 21. Above these in locations 13, 14 and 17 are 3 identical unmarked single pole relays with integral fuses. What do you think ? Worth pulling?

My relay panel usage is completely different to that shown in Haynes or any other circuit I've looked at. How do you find the circuits for YOUR vehicle?

Incidentally I found ALL the headlamp adjusters seized or replace by nuts and bolts! Replacement kit ordered. I expect a huge improvement when the lights are correctly adjusted!
Cheers!
Pete

[bigherb]

This is the circuit for the dim dip lamps.

[syncroandy]

The GB lighting diagram is also here as a PDF:  http://syncrosport.com/info/wiring

Regarding the relays listed:

Position 3, #42 - Coolant shortage control unit - Normal fitment

Position 5, #53 - Radiator fan 2nd stage relay - Normal for the 200/300w fan, but for a 2.1 engine I would expect to see the 450w fan which has a separate relay at the A-pillar and none at position 5. Also the rad itself should be the thicker verion.

Position 8, #18 - X-contact relief relay - Normal fitment

Position 10, #19 - Intermittent wash/wipe relay - Normal fitment

Position 11, #72 - Rear window wash/wipe relay - Normal fitment for that option

Position 12, #21 - Flasher relay - Normal fitment

Re. the others fitted, the wiring would need to be inspected to establish their function.

[JonB]

Don't suppose you have LED bulbs in?

[Piratepete]

The GB lighting diagram is also here as a PDF:  http://syncrosport.com/info/wiring

Regarding the relays listed:

Position 3, #42 - Coolant shortage control unit - Normal fitment

Hi Andy
Interesting, in Cybil #42 is in location 4 which is listed as a 'spare' location. I wonder if the coolant level circuit was faulty at some time and someone took out the control unit to 'solve it' lol? I think that the temperature gauge and startup test would still work with that unplugged? Someting else to investigate! The list lengthens!!!!!!
BTW do you know what resistance the dimdip resistor should be?
Oh, bulbs are not LED.
Cheers!
Pete

[Piratepete]

Hi Andy
The 3 extra relays are dip left, dip right, and full beam both. Dip left and right probably triggered through the dimdip resistor.
Looks professionally installed. Will leave (resistor disconnected) for now - coolant level warning circuit takes priority - the switch is open circuit and the control module doesn't seem to operate!
£50 worth of headlamp adjustors and mounts now installed and all properly adjusted. Looking forward to a night drive!
Looks like I have the standard fan and rad. I'm not concerned as engine temperature  and cooling seem fine.
Thanks for your help.
Cheers!
Pete