Fuses Blowing

[Walker sim]

Hi All,
When I try to engage OD on my Healey 100 BN1 (with a BN2 gearbox), both the 50A AND the 35A below it, blow. Any ideas Why?

Cheers,
Wally Simpson

[BJ8Healeys]

Hi All,
When I try to engage OD on my Healey 100 BN1 (with a BN2 gearbox), both the 50A AND the 35A below it, blow. Any ideas Why?

Cheers,
Wally Simpson

Wally, it sounds like something is wired incorrectly. Normally, the overdrive is not fused but the pull-in coil in the overdrive solenoid draws a lot of current (about 24A) for a short period of time (until the holding coil is energized, then the current drops to about 1A.) I'm assuming the BN1 or BN2 overdrive wiring is the same as a BJ8. Perhaps the attachment will help you troubleshoot it.

Good luck!

[Keoke]

Hi All,
When I try to engage OD on my Healey 100 BN1 (with a BN2 gearbox), both the 50A AND the 35A below it, blow. Any ideas Why?

Cheers,
Wally Simpson

When did this problem surface ??

[Walker sim]

Hi Keoke
About two months ago, previously OD worked fine. I replaced both fuses, engaged OD & again, both fuses blew.
Cheers,
Wal

[Bob_Spidell]

Hi Keoke
About two months ago, previously OD worked fine. I replaced both fuses, engaged OD & again, both fuses blew.
Cheers,
Wal

Did you use the proper fuses: 'slow-blow,' with the proper rating (the English rating is different than the ones you can typically get at the local parts house)?

[Walker sim]

Did you use the proper fuses: 'slow-blow,' with the proper rating (the English rating is different than the ones you can typically get at the local parts house)?

Yes, What I can't understand, if there is a problem within the OD, why do both fuses blow at the same time. I obtained the 50A from "Element14" in Aussie. Voltage rating VAC250V (made in China on the packaging). I wonder if there is a fault in the fuse block.

Cheers,
Wally

[John Turney]

According to the Bill Young BN1 wiring diagram in the January 2019 Healey Marque, power for the OD comes from the fused side (terminal A4) of the 35-amp fuse (This is different than later Healeys). The 50-amp fuse should only go to the horns. The supply side wire to the fuses should be brown (terminals A1 & A3); the fused wire to the horns should be brown with a green stripe (terminal A2). The fused side wires from the 35-amp fuse should all be green (terminal A4).

You could have a connection between terminals A4 and A2, causing power to the OD to go through both fuses. Check the fuse block for this. With a short in the OD circuit, the current is enough to blow both fuses, probably the 35-amp one first, then the 50-amp one.

The next problem could be the OD solenoid or a wire in the OD circuit shorted to ground (earth). Anyone know the inrush current of the OD solenoid?

[Healey Nut]

Divide and conquer ..... disconnect the wire to the solenoid . Install new fuses and with the OD solenoid wire taped off to prevent short . Turn on OD switch .... do the fuses blow , no connect solenoid with switch on , fuses , blow , yes , bad solenoid .
Fuses blow with solenoid disconnected and wire taped off , short in wiring or fuse block . This is not complicated .

[Walker sim]

According to the Bill Young BN1 wiring diagram in the January 2019 Healey Marque, power for the OD comes from the fused side (terminal A4) of the 35-amp fuse (This is different than later Healeys). The 50-amp fuse should only go to the horns. The supply side wire to the fuses should be brown (terminals A1 & A3); the fused wire to the horns should be brown with a green stripe (terminal A2). The fused side wires from the 35-amp fuse should all be green (terminal A4).

You could have a connection between terminals A4 and A2, causing power to the OD to go through both fuses. Check the fuse block for this. With a short in the OD circuit, the current is enough to blow both fuses, probably the 35-amp one first, then the 50-amp one.

The next problem could be the OD solenoid or a wire in the OD circuit shorted to ground (earth). Anyone know the inrush current of the OD solenoid?

Thanks John, I'll check the fuse block, strangely, with both fuses blown the horns still work but the wipers don't.
The car was restored 30 odd years ago then placed in a collection with little use until I bought it. Maybe the correct color wires weren't used which could make it difficult, I'll check.

Cheers,
Wally

[Walker sim]

Thanks Jedi, Sounds simple, I'll have a go

Cheers, Wally

[vette]

I think maybe some wires at the fuse block got switched around. The horn should be on the fused side of the 50 amp fuse not the power in side. If I remember right it is easy to get a short between the two fuses. Something moves or one of the wires touches both fuses. So look closely at your fuse block. The to investigate the OD i would firstly look at the wires to the dash switch including the dash switch. The dash switch may have internally shorted to ground. Take the wires off the dash switch and check the switch with an ohm meter or continuity tester to see if it is shorted. Then test for a break or short on each of the wires. Take the other end of those wires off the OD Relay at terminals C1 and W2 before testing these wires. Then another test would be while these dash switch wires are off, use a jumper across therminals C1 and W2 to see if the OD energizes properly that way. If so, then the circuit wires to the dash switch are what causing the problem. But I also think you have something wrong at your fuse box, look it over carefully.

[Walker sim]

Thanks Luke, I feel the problem is in the fuse block. I will start with there.