The Triumph Dolomite Club - Discussion Forum

Fitting an Overdrive On indicator light
Page 1 of 1

Author:  Robert 352 [Tue Aug 12, 2014 12:10 am ]
Post subject:  Fitting an Overdrive On indicator light

I have often noticed when I sit in a modern motor car that there are lights providing all sorts of information.

I find myself forgetting to disengage the overdrive which comes about perhaps because the car is so quiet or I am distracted as I drift up to a set of traffic lights so that I simply forget, as I glide to a halt.

An overdrive on light might somehow remind me, when it is on.

I wondered what I could do that would not deface the dashboard in any way. The warning light cluster has no “spare” lights but that set me thinking that perhaps I could use one of the existing lights. The most obvious one is the Handbrake On light.

Then I noted that mine was not working. It was time for some investigation.

I had to remove the front seats to remove the carpet covering the handbrake mechanism and then tweak the little switch slightly so that the light came on when the handbrake was engaged. It seemed to me there was no reason at all why I could not use this light also as an overdrive on light. It does not have the correct logo on the glass but since it is not a red light – a warning, but amber and therefore a different colour it would be just fine.

Making the connections would be easy for it requires no more than two of those piggy back spade connectors, one on the handbrake switch and one on the overdrive solenoid and a couple of lengths of wire – as seen here with one of the piggy back connectors sitting just above the handbrake mechanism.
20140812-4851Pw Dolomite handbrake lever.jpg
20140812-4851Pw Dolomite handbrake lever.jpg [123.88KiB |Viewed 1215 times ]
However it was not quite as easy as that for the handbrake warning light is activated when the handbrake lever switch provides the earth to the light – in much the same way as the courtesy light switches in the door pillars activate the interior light. The overdrive solenoid is activated when the gearlever switch provides 12 volts to activate it.

The solution? I used a relay which is activated when the overdrive switch activates the solenoid and then through the relay contacts it provides another earth path for the Handbrake On light.

I had some spare wires left over from one of the several Dolomites which arrived here in parts over the years. They yielded a pair of wires with the single connector which could sit alongside the wiring loom which comes up from the gearbox and which can be unplugged if and when the gearbox is removed from the car. Another piece of wire runs from the handbrake mechanism alongside the tunnel cover but on the left hand side and runs up to the relay which I have mounted in behind the glove box using one of the heater mounting bolts to hold a simple plate to which the relay has been screwed.
20140811-4849Pw Sprint overdrive indicator relay.jpg
20140811-4849Pw Sprint overdrive indicator relay.jpg [108.16KiB |Viewed 1215 times ]
The result? Turn the ignition on and if the handbrake is activated then the indicator light will be on. It can only be the handbrake unless you happen to start the car engine in third or fourth gear with the overdrive engaged, which in my case is most unlikely. I now have a clear indication of when the overdrive is engaged.

All without defacing the dashboard nor cutting into the existing wiring in any way.

It might be of interest to some, on the other hand it might not!


Author:  cleverusername [Tue Aug 12, 2014 12:36 am ]
Post subject:  Re: Fitting an Overdrive On indicator light

Interesting, I had thought of a similar idea. The obvious light to change would be that pointless seatbelt warning light. Just write overdrive there instead.

Author:  Robert 352 [Tue Aug 12, 2014 5:06 am ]
Post subject:  Re: Fitting an Overdrive On indicator light

I have the earlier model which does not have that seatbelt warning light, unfortunately.

A good suggestion though.


Author:  xvivalve [Tue Aug 12, 2014 7:48 am ]
Post subject:  Re: Fitting an Overdrive On indicator light

So what happens if you drift up to the red light with overdrive engaged but apply the handbrake before you glance at the dash... :-P

Author:  Jon Tilson [Tue Aug 12, 2014 8:36 am ]
Post subject:  Re: Fitting an Overdrive On indicator light

All you can ever achieve with this is a solenoid status indicator. It doesnt tell you if overdrive is or is not engaged,
which is a function of various things to do with oil pressure and cone clutch position.

Its already wired up to prevent engagement in low gears and reverse when damage may occur. Sadly a sticking solenoid can still cause this trouble.

Other than that the rev counter and hearing should tell you all you need to know.

All goof fun though....and if you think its useful this is how to do it.


Author:  TrustNo1 [Tue Aug 12, 2014 9:46 pm ]
Post subject:  Re: Fitting an Overdrive On indicator light

Isnt on/ off written on the switch itself, if not buy a new switch.

Author:  gmsclassics [Wed Aug 13, 2014 12:51 am ]
Post subject:  Re: Fitting an Overdrive On indicator light

Mmm. Yes mine does have on/off written on the switch - but I can't see it with my helmet on - yes forwards is off and back is on - but then in the heat of a race my poor brain is trying to cope with more than it is obviously capable of. That is also why i have this big blue stobe to tell me when to change up a gear! The thought of dropping out of overdrive when the engine is at 7500 and ending up at 7500/0.797 is enough to make me want to do something to remind me I am in overdrive! Hence this somewhat more in your face version:
dash od light.JPG
dash od light.JPG [116.05KiB |Viewed 1139 times ]
The light is so bright - as it has to be to be instantly visible in bright sunlight - but it is actually a dual red and yellow light, red is connected to the oil warning light (as chances are I wouldn't be looking at the oil pressure gauge when I lost oil) as well as the yellow indicating the overdrive is engaged. Yes it is wired into the solenoid circuit, but the chances of the overdrive being engaged when the solenoid isn't energised is slim.

I was trying to also set it up so that the light only came on above about 5500 revs and a few on this Board were trying to help, but my limited capacity to understand electronics won the day.


Author:  Jon Tilson [Wed Aug 13, 2014 10:00 am ]
Post subject:  Re: Fitting an Overdrive On indicator light



Author:  john whitehead [Sun Jan 16, 2022 5:17 pm ]
Post subject:  Re: Fitting an Overdrive On indicator light

Hi Robert, I stumbled across your article whilst researching the handbrake- on switch.
I might not be able to replace it,( if it can't be freed up ), but I like the idea of seeing an indication of being ON overdrive without feeling the gear knob or looking down.
I've read the negative comments but I don't speed enough to get to the traffic lights on overdrive!
I understand that it might not strictly ALWAYS be showing the real position of the overdrive but I like it If anyone has a functioning switch as in the picture please contact me on 01271 866213
Thanks for the idea, Regards, John

Page 1 of 1 All times are UTC
Powered by phpBB® Forum Software © phpBB Limited