Overdrive Fuses

From Peter Schauss

Originally published in the Austin-Healey Magazine, January 1997

(For some reason, the original fused line to the overdrive harness was replaced with an unfused one. On BN1s, the overdrive line ran off the fused side of the ignition line. As early as the BN2,however, it was attached to the unfused side of the fuse bloc, possibly in a move to minimize the number of connections on the fused side. Here are one owner’s comments as taken off the net. –ed.)

After toasting my overdrive solenoid last year, I installed a fuse to protect the new one and I can confirm that the fuse does work. Driving on the parkway yesterday, my Healey spontaneously dropped out of overdrive. When I got home, I checked the in-line fuse, which I had added and it was blown. I pulled the gearbox tunnel cover off, removed the solenoid, and took the protective cover off. Sure enough, the points, which are supposed to cut out the pull in winding, were not opening when the plunger came up. I adjusted the points by bending the copper strip, replaced the solenoid, and checked the lever adjustment as per the manual. On my way to work this morning, the overdrive worked fine. Without that fuse, I would be out another $75 for a new solenoid. Needless to say, I strongly recommend this electrical modification.

I added the fuse to the white wire which runs from the unfused side of the fuse block to the C2 connection on the overdrive relay. As noted, the solenoid was only slightly more than a year old when it failed so it most definitely pays to check the contact on these things anytime you happen to have the tunnel cover off.

Sorry, I should have mentioned that I think that I was using a 20 amp fuse when it blew. I have a 15 amp in there now. The important thing is that it should be a slow blow fuse. The pull-in winding draws more than 30 amps, but only for a fraction of a second (if the solenoid is working properly). So you need a fuse which will give the pull-in winding time to do its job but not enough time to cook anything if it stays on.

In my case, the 20 amp fuse was sensitive enough to do the job. The solenoid had that familiar wood-smoke smell when I pulled it out so I know I came pretty close to cooking it.

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