Dim and dimmer

[phillpot]

Been having a play with the instrument lighting this evening, my car has a rotary switch..off...dimmed...bright..

"bright" is straight forward, bulbs receive a full 12 volts.

"dimmed" is achieved by putting two 1.5 ohm ballast resistors connected in series in circuit, electronics aren't my strong point but I guess that gives 3 ohms?

So, checking out my resistors one measured 2 ohms, near enough (my cheapo multimeter may not be bang on) other came out at 9 ohms ! No wonder lights were dim.

Next step was to try with just the good 2 ohm resistor, not bad, a definate change but still legible.

Any normal person would probably have bought two new ballast resistors but I thought these looked neater...



They are rated at 2 ohms each, couple of pounds for the pair from Ebay. Soldered some connectors on to take "standard" spade connectors

Not the best photo's but it's results time, first 12 volts



Good ballast resistor or one RS resistor (no noticeable difference) approx 9 volts and less camera shake



Two RS resistors in series approx 6 volts and can't see the needle so not too good



So I shall go with just the one and now I just need to knock up a little bracket, must have an off-cut of stainless somewhere

[kevroe]

Good fiddle. Mine are like yours. Where is the wiring? Is it just stuffed up behind the steering wheel. It is pretty tight in there and I don't want to go pulling wires out willy nilly.

[blues3]

Yes they're behind the centre console.

Here's the schematic from behind the panel light / dimmer switch....



...and the circuit by itself....



Have a look here http://tvrs3.net/Electrics/Electrical%20Page.html

there may be other useful stuff.

Edited by blues3 on Wednesday 21st August 23:04

[phillpot]

kevroe said:

Where is the wiring? Is it just stuffed up behind the steering wheel.

The resistors are under the bonnet, fixed to the bulkhead sort of just above the oil filter.

[blues3]

Here....

[GadgeS3C]

phillpot said:

Any normal person would probably have bought two new ballast resistors but I thought these looked neater...

So I shall go with just the one and now I just need to knock up a little bracket, must have an off-cut of stainless somewhere

Normal people just bin the resistors to reduce the 0 - 60 time by 0.00000000000000000001s rather than find an excuse for a heavy shiny thing

Disconnected mine as even on no resistance they aren't the brightest of things. When I get around to upgrading the rest of the bulbs for LEDs I may reconsider, those resistors do look nice and shiny brackets - hmmmm

[lewdon]

I used 2.7 Ohm 50 watt which worked well and relocated from the bulkhead to next to the brake balance cylinder.
NB; it needs a heat sink and to be spaced away from the fibreglass as it gets very hot.

[phillpot]

lewdon said:

it needs a heat sink

Heat sink eh

this could come in handy, think it's an old dim dip module?



(suppose I could live with alluminium rather than stainless )

[lewdon]

That should certainly keep it cool, and look the dogs whatsits when polished up.

I just folded up the sides of a piece of sheet aluminium, cos that's what I had, and then used small stacks of washers as spacers.. (a piece of sheet StSt would have been blingier.)