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Healey 100 Overdrive stopped working

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Walker sim

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Hi,
The OD on my 100 has stopped working. I suspect a fuse but can't find it. Any clue as to where to start looking? The car is a BN1 with a BN2 gear box.

Thanks All, The problem is solved, someone had replaced the 50amp fuse with a 25amp. When I checked the fuse looked OK but the meter told a different story....Wally
 
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The link below is for a very good article and covers all the big Healey overdrive systems. Since the BN1 had a centrifugal switch that the BN2 does not have I can't be sure how yours is set up. Normally neither of them had a dedicated fuse and the OD was fused along with several other circuits on the same fuse at the A3 on the fuse block on the firewall. A common mod is to add an in line fuse that is specifically for the overdrive solenoid. You may or may not have one. There are multiple things that could be causing your overdrive to not operate. If it was the fuse at A3 other things would not work. It could simply be a broken wire or a bad solenoid. The cited article should help troubleshooting more than my guessing.
https://www.healey6.com/Technical/Tech-OverdriveTroubleshooting.pdf

Good hunting. Let us know.
 
Start with the solenoid itself - do you have a tester? If so, set it up for Ohms and set one clip on the wire from the solenoid and another to ground. It should read 5ohms or so. Then manually engage the OD (Push up the plunger) and you should see the solenoid jump to 12-14ohms. If not, bad solenoid and you should replace.
 
Before you go digging into the overdrive to test the solenoid, test the dash switch. It's easier to get to.
 
Buy extra fuses. You might need them if there is an unknown reason why it blew in the first place.
 
The OD on my 100 stopped working 2 separate times. First time, as John said, my original dash switch finally bit the dust. The second time it was the switch on the side of tranny that is activated by gear shift lever in 2nd and 3rd gear. If that switch fails, current doesn't make it to solenoid.
 
Walker sim said:
Thanks Kurts100, the fuse, 50amps! (someone had changed with a 25amp), all good now.....Wally
Click to expand...

Hope that's a slow blow fuse; like any inductive load--motors, solenoids, etc.--the OD solenoid is essentially a dead short for a couple milliseconds. Moss, I believe, sells the correct one.
 
My recollection is that the pull-in (intermittent) draw is 18 amps and the hold-in (continuous) draw is 2 amps, but I certainly agree with Bob that a slow-blow fuse is in order as you are essentially in a "locked rotor" situation.
 
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