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BJ7 overdrive

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Tproject

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My BJ7 started to engage OD whenever 3 or 4th gear is selected no matter what the OD switch or throttle position. Did a continuity check of all components and the relay has all connectors hot.
My question is---the BJ7 relay is priced $137 more than the BJ8 relay---are they interchangable?
 
I don't think your relay is the problem. It is a slave of the OD switch and the throttle switch and the transmission switch. (It receives power from those switches only) Engagement occurs when both the OD switch is on and the trans selector is in 3rd or 4th. The throttle switch only comes into play to override the OD switch if the OD is engaged and the OD is switched off but the throttle is off; in that case it provides power to the solenoid to keep the OD engaged until the throttle is opened somewhat -- then it breaks the connection. I'd suspect a problem with the throttle switch providing power all the time, or the OD switch not switching off.
 
TimK said:
It is a slave of the OD switch and the throttle switch and the transmission switch. <span style="font-weight: bold">(It receives power from those switches only)</span>
Click to expand...
I don't think that is right. The relay has a white wire that comes directly from the un-fused side of the fuse block. I have sacrilegiously colored the white wire red for emphasis below. I do agree that another component may be the cause. I'd disconnect each switch and check for proper continuity.
 

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Whenever I try to answer someone's problem, I fear the experts will tell me I'm wrong. I'm down in Florida without my wiring diagram. So, Greg is always right because he either knows or researches his answers before chiming in. The diagram shows that the OD switch (71) and transmission switch (73)provide the ground path. So I just ran out of expertise. Good luck "Tproject".
 
Thank you all!

This one was a great puzzle with a good conclusion.
I tested each switch for continuity and the relay & throttle switch for proper function and then it worked! & shortly after it didn't.

Then I recalled that early on I pulled out a second OD switch I had from my parts BJ7 to change out with mine but I canceled that when it proved bad on a continuity check (weak link?)so----I went back to the switch in the car which had tested ok, removed it again and checking continuity, it started to stick on about 3 out of 5 times. Ordering a new switch today.

Lesson, if you lose your way on the trail, backtrack & start again.
 
If we saved you the cost of a new relay, the discussion was worth it even if a few facts given were incorrect. Thanks for sharing your journey.
 
If Keoke was on board, we'd all learn how a relay works. I need to do more research on this. I miss Keoke...
 
Dave did that post as an answer to my problem. If you study it carefully, you will see the logic and its very simple to test and rebuild. Don't get into that replacement mode. This stuff is easy to fix. There is also some good stuff on this in Norman Nock's, "Tech Talk".
 
Greg, thanks alot. I also miss Dave Russell, but it's good to have the rest of you guys who remember his contributions and bring them to bear at the right time.
 
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