Electrical Gremlin on Sequential Box

[Grats]

Any thoughts on an unusual electrical fault on my Clio Rally car. Well unusual to me, might be something very simple.

Problem - Car is running a sequential box with custom built digital gear display.
The Sadev gear position switch and gear position display work on 5v supply. They are fed from a 12v to 5v converter.

Everything works fine until I turn on the interior fan. Then rather than having 5v feed out of the converter it is 12v out and in and of course the display stops working.

Tried a dedicated earth and 12v supply direct from battery in case their is a cross feed or bad earth - no luck.

Thought it might be an earth fault but everything seam ok and would expect more issues?

The loom is a stripped down standard loom, using same fuse box, loom came with shell so can't be 100% sure what's been done.

Any thoughts, guesses, testing ideas.

Thanks

 

[Grats]

Done a bit more testing, even more confused.

Right with the internal fan switch off the 12v to 5v converter gives a 5v supply, with the fan switch off but fan itself unplugged it gives a 11v output. With the fan still unplugged but internal switch on any setting get 12v instead of 5v. Any suggestions??

 

[sam JFM]

Does it work with a separate supply and the fan off?

 

[Grats]

hi Sam

Ran a supply direct from battery and a dedicated earth, and just the same, works with fan connected but not turned on, turn fan on (setting 1 ,2 or 3) and voltage jumps to 12v. If the fan is disconnected and then turned on jumps to 8v on setting 1 and 11v on 2 and 3 speed settings.

Cheers

 

[sam JFM]

What happens to battery voltage when the fan is unplugged and the switch is on?

 

[Grats]

Hi, don't think I have measured this, will try to have a look tonight.

For the next event a roof vent is being installed.

Cheers

 

[Grats]

Hi Sam - tested voltage across battery and no noticeable voltage drop with or without switch on, plugged or unplugged motor.
Cheers

 

[Grats]

All sorted I think, one of the fan actuator wires which are not used was cross to earth, so when fan on feeding back.

Thanks