Blown main fuse

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Model T Ford Forum: Forum 2017: Blown main fuse
Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Saturday, January 21, 2017 - 11:08 am:

Started out to breakfast this morning and blew the 30 amp main fuse. Changed it and blew it again. Quick visual inspection and found nothing except some slightly loose connections at the terminal block. Could this cause higher resistance and be the cause? Ideas? Suggestions? Thanks. John


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Saturday, January 21, 2017 - 11:12 am:

If you have an open (loose, intermittent) connection between the generator and the battery the generator starts to go into runaway overcharging. That can blow the fuse. Or it could be a shorted cutout or voltage regulator.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Saturday, January 21, 2017 - 11:18 am:

Thanks Royce. Running an alternator and the fuse is between the battery and the terminal block.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Saturday, January 21, 2017 - 11:35 am:

Put another fuse in and the ammeter indicates a 10 amp steady charge. Becker alternator. Usually drops down pretty quickly. Something wrong? Could this blow the main fuse?'


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Saturday, January 21, 2017 - 11:39 am:

An alternator can charge at 50 or 60 amps. A 30 amp fuse will blow if the battery is low and the fuse is in the charging circuit.

I would make sure that the alternator + lead is not in the fused circuit. The fuse should protect all the other circuits in the car, not the charging or starting circuits.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Saturday, January 21, 2017 - 11:46 am:

OK Royce. Thanks again.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Saturday, January 21, 2017 - 12:13 pm:

Alright. Making progress. Found that turning lights on either high or low beam results in immediate full discharge indication. Must be a short in the lighting circuit or the switch is bad. The search begins.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, January 22, 2017 - 12:47 am:

Glad you had a fuse in there. That saved you so don't defeat it. Find the wiring short in the lights and fix it and all will be well.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Sunday, January 22, 2017 - 08:54 am:

You bet! I am inclined to think it is the switch since it does the same thing on bright and dim. It is about a five year old repro. I'll pull it out and check because I'm not sure how to go about meter checking the wiring.


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