J type overdrive wiring

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Llessur
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J type overdrive wiring

#1 Post by Llessur » Mon Apr 09, 2018 11:04 am

Regardless of whether a relay should be fitted (I intend to fit one), an I right in thinking that the factory wiring for the J type overdrive was a postive feed from the reverse light circuit running to one terminal of the inhibitor switch then from the other terminal of the inhibitor switch to one terminal of the gearstick switch, then from the other terminal of the stick switch to one terminal of the solenoid (the other solenoid terminal being earthed).

If so, then why on my rebuilt j-type gearbox would one terminal of the inhibitor switch have an earth wire running to a gearbox casing bolt?

Is there an alternative wiring method where the negative side of the solenoid is switched? Is either preferable?
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White

My 2500 blog: https://triumph2500blog.wordpress.com/

Clifford Pope
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Re: J type overdrive wiring

#2 Post by Clifford Pope » Mon Apr 09, 2018 5:17 pm

Both my Haynes and Autobooks do indeed show an inset wiring diagram with the inhibitor switch earthed, the other terminal being connected to the operating switch.

The relay has 4 wires to 4 terminals:
W1 = White wire to ?
C1 = Brown wire to ?
C2 = Yellow/Purple wire to overdrive solenoid
W2 = Yellow/Green wire to operating switch

I can't find anything on the wiring diagram that shows where the white and brown wires go. They are marked as "a" and "b" but these don't appear on the main wiring diagram.
I presume one must be a live feed from somewhere, but I don't understand what the other does.

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Re: J type overdrive wiring

#3 Post by Clifford Pope » Mon Apr 09, 2018 5:27 pm

Got it. There is another wiring diagram in the main text, amplifying the one at the back.
The White wire, now marked (2) goes to the starter solenoid, the Brown wire marked (1) goes to the SW terminal on the coil.

Also the relay diagram now explains that the earth to the relay is supplied via the inhibitor and operating switch in series, and when that circuit is made the relay supplies a positive feed to the solenoid.

tony
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Re: J type overdrive wiring

#4 Post by tony » Mon Apr 09, 2018 6:47 pm

Recently rewired mine and removed the relay I have had for years to simplify wiring. Solenoid only draws 2 amps.
Live feed from ignition to gear lever switch, other side of of switch to inhibitor switch, other side of this switch to solenoid, other side of solenoid to earth. Simple, seems to work ok.
Tony.
1976 2500 TC. converted to S specs.

Lots of bits

1999 BMW Z3.
2006 BMW 325ti.
Hopefully not needing too many bits.




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tony
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Re: J type overdrive wiring

#5 Post by tony » Tue Apr 10, 2018 5:12 am

Forgot to mention I also fitted a line fuse between live feed and gear lever switch.
Tony.
1976 2500 TC. converted to S specs.

Lots of bits

1999 BMW Z3.
2006 BMW 325ti.
Hopefully not needing too many bits.




.

Mike Stevens
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Re: J type overdrive wiring

#6 Post by Mike Stevens » Mon Apr 23, 2018 1:22 pm

Although the 'J' type only draws 2A running current, the inrush current when you first engage the overdrive is much higher. I have had to repair the gearknob switch a few time with 'J' types but not with 'A' types due, I believe, to this higher inrush current damaging the switch contacts.

I think having a relay in place is a good idea for both types of overdrive as it limits the switch current to less than 100mA, leaving the relay to take the higher current load.

Just my 4p worth!

Cheers,
Mike.
(South Oxfordshire)
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1971 2.5PI Saloon Sapphire blue
1973 2.5PI Saloon rust some Honeysuckle
1973 Stag French blue
(1949 LandRover was blue should be light green!)

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