Overdrive Wiring

Durango2k · Post by **Durango2k** » Sun May 29, 2016 8:44 pm

Hey guys,

how should I wire my Overdrive ?

I have looked for the wiring diagram- I remember I have seen one once hand- written- but cannot find it.

I do have a working rear light switch in the gearbox, and a second switch which methinks is a 3rd / 4th gear switch (I can measure how it behaves when I put the gearbox in 3rd and 4th).

I invented one myself on paper - but it has one flaw: it relies on the information that power flows through the reverse light switch to decide wether the OD is allowed to be switched on.

IF now the rear light bulb blows, then the OD can be engaged in rearward mode - because the relay would not pull and so not hind it from engaging.

Oh and I thought I should use the heated rear screen switch for the OD. I won't need it anyway, it can easily be reversed, so no changes to the dash.

Carsten

MarekH · Post by **MarekH** » Sun May 29, 2016 9:35 pm

Rather than only send power to the rear lights, use it to power a changeover relay so that power can only go to rear lights OR the overdrive.

Then take that to another relay (a starter relay would be best) for the overdrive and power the overdrive directly through that using a fused brown wire. (The other side just goes to the green/brown for the reverse lights as per before.)

The overdrive solenoid uses 0.9amps once running, but over 15amps to initially fire the overdrive. It is possible for this solenoid to stick, so it is inappropriate to power it directly from any green wire, as it'd pull enough current to melt the wiring and your overdrive select switch. (The 4th gear switch is quite robust.)

Search the j-l forum for my more detailed answer on this and the James Bond switch.....

kind regards
Marek

Durango2k · Post by **Durango2k** » Mon May 30, 2016 2:53 am

Hey,

thanks for that- that would of course work.

I came up with a more simple solution, what'ya say ?

Take power from the reverse switch, just because it is near. Feed it through the 4th gear switch, and then through a simples starter relay, and then through dashboard switch (Jimmie Bondi or whatever).

All in series, effectively. 4th gear switch, relay and manual switch on dash.

This relay when switched sends power to the solenoid on the OD.

This way it is not relying on the rearward gear light, it only can activate the solenoid if in 4th gear (else no power behind the switch to activate the relay) nor can it ever be activated without user wanting it.

?

It's actually simpler then a changeover relay...

???

Carsten

cactusman · Post by **cactusman** » Mon May 30, 2016 5:18 am

If you have a fourth gear switch you do not need to use any feed from reverse. Just take a feed from the ign live side of the car via a 20 amp fuse to your dash switch. From there to the fourth gear switch and from there to the OD solenoid. If you have the wiring loom for the heated screen use that but connect to your fourth gear switch instead of the screen.

Only if you do not have a fourth gear switch would you need a relay operated by the reverse light to disconnect the feed to the OD if it is on . Never move the car in reverse if you think the OD is engaged. Bad s@@t happens to the overdrive.

David Oslo · Post by **David Oslo** » Mon May 30, 2016 7:18 pm

I wired mine up after studying manuals from XJ6 and TR's and Laycock. It's just like Carsten wrote on his second posting, you jump the live feed that is there anyway (feeding into the reverse 'switch' on top of the gearbox) take that and feed across and into the new overdrive gearbox swith (the Lucas plunger type) so that it also has a live feed, then the output of the overdrive switch goes to the manual switch (which on my car is on the gearknob) then further onto the overdrive solenoid. At least it all seems to work when I sit and "pretend" driving, with the car still on axle stands :-)
The XJ6 (the MOD box) only allows overdrive engaged on 4th gear.

MarekH · Post by **MarekH** » Mon May 30, 2016 7:36 pm

Look guys - I won't bother again.

It pulls 19amps to fire the solenoid. It only does that for an instant and then it's down to 0.9amps. Except when it sticks, then the wiring melts within 1 second. I've seen it happen.

Use a fused relay or don't do it at all. Wiring it into a 50 year old bit of green wire that could safely take about 7 amps maximum 50 years ago whilst backed by a blanket 35amp fuse is just plain stupid.

kind regards
Marek

Durango2k · Post by **Durango2k** » Mon May 30, 2016 7:44 pm

Now,

Of course I will use fresh Arizona copper wire, and use a relay. Plain connecting it is stupid of course.

But logistically it's the simplest and safest way to do it - you can only use it in 4th, so I won't destroy it rearwards...

Carsten

Link:
BBcode:
HTML:
	Hide post links

Link:
BBcode:
HTML:
	Hide post links

Link:
BBcode:
HTML:
	Hide post links

Link:
BBcode:
HTML:
	Hide post links

Link:
BBcode:
HTML:
	Hide post links

The 'E' Type Forum

Overdrive Wiring

#1 Overdrive Wiring

#2

#3

#4 Overdrive

#5

#6

#7