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Overdrive Electrics

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Chet Zerlin

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Hi all,

As a part of the restoration of my BN6 I'm replacing the grungy electric parts on my firewall. Each time I replace one I test drive to make sure the replacement (from Moss Motors) is working properly.

My overdrive was working perfectly fine, but now that I've replaced the switch on the firewall (throttle switch?) it does not work. I'm wondering how to test the new switch to see if it is defective. Is there some adjustment that I needed to make on the new switch to have it properly work?

I did note that the old switch had no resistance at all on the lever arm while the new switch does have resistance (and sounds like I am stretching a spring of some type when I move it).

Thanks!
Chet
 
Don't forget there is an OD relay ( three wires go to that) and an OD throttle switch (with two wires and a rod attached to the throttle motion). Since you didnt dither with the relay, that is probably fine. With one wire disconnected from the throttle switch ( doesn't matter which one) measure resistance across the switch. With the throttle closed (accelerator not depressed) there should be no resistance across the switch. Full continuity because in that position the switch should be closed. Move the accelerator pedal or disconnet the rod at the switch and move the arm to a position between about 1/5th to 1/3rd open throttle ( this should correspond to the amount that you " blip" the throttle when you disengage the OD) The throttle switch should open and you should see infinite resistance. If the switch doesnt open or if the switch is opened to begin with, there is something wrong. Report back.

View attachment Healey overdrive.pdf
 
I meant to say 3 terminals on the overdrive relay, not 3 wires. There are actually 6 wires, two on each terminal.
 
A


Put old SW back in see if it works ???
 
As the saying goes , “if it aint broke dont fix it”
 
I thought it was " If it ain't broken, break it". Then you know it's broken...no troubleshooting needed.��
 
To test any switch, use the continuity setting on a multimeter. As John said, the throttle switch does require adjustment.

I thought the saying was "If it ain't broke, fix it again" when it comes to these cars.
 
Thanks everyone for your replies.

As suggested I tested the throttle switch and it is open regardless of where I move the arm. I put the old switch back on and my overdrive went back to working fine. New switch is going back to Moss tomorrow for a refund. Meanwhile I cleaned up the old (working) switch enough that I'm happy to keep it on my newly sparkling firewall.

Thanks again!
Chet
 
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