Fuse keeps melting down

[SRQJeff]

Hey, folks. The good news is that, after a slumber of between 15 and 20 years, my SV started yesterday with very little coaxing. Thank goodness for the Weber. The old Strombergs would have been basket cases by now. But a problem has suddenly cropped up. Every time I turn the key on, a fuse blows instantly, with a nice white flash. I've narrowed it down a bit. If I disconnect the double white wire on the ignition switch, it doesn't happen, so it must be something connected to that. Any ideas? I am using a 30-A U.S. fuse. I read the post recommending Lucas 35-A ones, but I can't remember the last time I saw one of those.

 

[Ken Ellis]

Resist the temptation to increase the fuse size... lest your wiring harness become the fuse. Study up on the wiring diagram, and try to determine where the two white wires from your switch ultimately go. Tach and coil, maybe? Or is it the accessory feed? And, yesterday it ran, and now it blows fuses?

 

[puff4]

Yes, do NOT increase the fuse. Frankly, since you are using US 30A fuses, you already have. British fuses are rated at 'blow' rating, so a 30A is actually for a 15A circuit and blows out at 30A. US fuses are rated at circuit load, so a 30A fuse is for a 30A circuit and won't blow unless the load is far higher than 30A (around 70A!).

So, when you get this sorted, *please* go back to the original Lucas fuses... they are more expensive, but they are more likely to save your wiring. If you absolutely *must* use US fuses, shoot for one that's rated 12.5-17A, since that's the nearest equivalent.

You can easily get Lucas 30A fuses online. Here's one source, for example:

http://www.triple-c.com/Products_and_Accessories.cfm?pn=FUSE30/5&pID=1301

 

[SRQJeff]

Fuse issue

Resist the temptation to increase the fuse size... lest your wiring harness become the fuse. Study up on the wiring diagram, and try to determine where the two white wires from your switch ultimately go. Tach and coil, maybe? Or is it the accessory feed? And, yesterday it ran, and now it blows fuses?

Hey, Ken. Yes, it looks like one wire goes through the tach and on to the coil from there. The other goes to the fuse box. It still runs fine, so I tentatively assume it's not the coil. But I disconnected the tach, and it still happens. I don't know what's left. The panel lights work OK, but I think that's an entirely different circuit.

I'll install some Lucas fuses when this gets straightened out, but they won't do me much good now. The manual actually says 35 A fuses, but I guess 30 is close enough. It looks like SS stocks them for $.85 each.

 

[sunbby]

The white wires from the ignition switch feed the switched 12 volts from the battery to the coil and to the fuse block. Everything connected to the white wires must be ok because the car wouldn't run if there was an issue.

I assume the fuse between the white wires and the green wires is the one that blows? So the issue is something connected to the green wires. There is a SV wiring diagram on the website, in case you don't have it yet:

http://www.sunbeamalpine.org/downloads/wiring_diagrams/s5_diagram.pdf

You could start disconnecting green connections. A multi-meter would be useful so you don't need to keep going through fuses. You could check the resistance between the fuse and a ground somewhere. With all green wires connected (and key off, or better yet fuse removed) you will probably measure a very small resistance. Then disconnect green wires until the resistance increases, that should be the culprit.

My guess is the wiper motor, second guess is the horns.

Good luck.

 

[SRQJeff]

The white wires from the ignition switch feed the switched 12 volts from the battery to the coil and to the fuse block. Everything connected to the white wires must be ok because the car wouldn't run if there was an issue.

I assume the fuse between the white wires and the green wires is the one that blows? So the issue is something connected to the green wires. There is a SV wiring diagram on the website, in case you don't have it yet:

http://www.sunbeamalpine.org/downloads/wiring_diagrams/s5_diagram.pdf

You could start disconnecting green connections. A multi-meter would be useful so you don't need to keep going through fuses. You could check the resistance between the fuse and a ground somewhere. With all green wires connected (and key off, or better yet fuse removed) you will probably measure a very small resistance. Then disconnect green wires until the resistance increases, that should be the culprit.

My guess is the wiper motor, second guess is the horns.

Good luck.

Hey, Todd.

Thanks for the info. Yes, we're talking about the fuse between the green and white wires, farthest from the engine. It's been a long time, so I don't know if all of the wires are connected right. I have one double green wire and one single one connected to that fuse. There is another green wire connected to the second fuse. That one plugs into its own chunk of harness and disappears down by the tranny. Wrapped up with it there's green/red wire that plugs into another green one that goes through the firewall. Right now, it isn't connected to anything.

I looked at my parts car, and it has all of the green ones connected to the same fuse and a blue wire connected to the other fuse. But it looks like the blue one isn't original, because it isn't wrapped up with anything else. It just goes into the firewall by itself.

The wiper motor doesn't run, so maybe that's the problem. I did notice that a horn wire was pinched and possibly shorting, too. But wouldn't that be a non-issue until I try to honk the horn? All of the steering column stuff is disconnected right now.

I did try the meter. The green wires on the first fuse show a short whether connected or not. The other one doesn't, either way.

Could it possibly be a fried instrument voltage regulator?

Thanks again for your help. Once I get this electrical stuff straightened out, I can get on to the new interior.

 

[Ken Ellis]

Todd's got you going down the right path here. I'd recommend labeling, then disconnecting, the wiper motor, horns, etc. to control your variables. (Clearly label each wire of the device.) Keep in mind the switches for these devices could have problems, too -- horn switch in wheel, etc.

An instrument voltage regulator wouldn't normally fail as "shorted", but I suppose it could happen. Could be tangled wiring shorting out, too.

(If you had a starter solenoid that had a separate ballast resistor bypass terminal, and it was replaced with a solenoid without the special terminal, some inadvertent mis-wiring could have occurred.)

Keep in mind -- just speculating.

Best thing is to sit down with the wiring diagram and work on understanding it well... Then see how closely the car matches the diagram.

There's a color-coded wiring diagram out there somewhere... worth the search.

On edit -- that's the one Todd linked to...

 

[mikephillips]

Along with what's been mentioned, look for broken insulation, bare connectors and such. Electricity will follow the path to ground and can take some round about paths to get there.

 

[todd reid]

fuses keep melting down

Actually the horns could be the problem. They have voltage going to them at all times. Pushing the horn ring completes the ground side of the circuit. If a wire taking power to the horns was grounding it could cause the symptoms you have.

 

[SRQJeff]

Oh, yeah

Actually the horns could be the problem. They have voltage going to them at all times. Pushing the horn ring completes the ground side of the circuit. If a wire taking power to the horns was grounding it could cause the symptoms you have.

Oh, yeah. Good point. I'll check that, too.

I'm thinking that even if I have a green wire connected to the wrong fuse, it won't make much difference. Whatever is connected will get power with the key switched off or on instead of only on, but that shouldn't hurt anything.

Unless I'm missing something, the wiring diagram doesn't show anything connected to that fuse except the interior lamp and switch (GT models only). So it would appear that it isn't used for anything on the SV.

I don't know. I'll screw around with it until I figure it out. Thanks.

 

[SRQJeff]

Yeah, that was the problem

Apparently, the horn was the culprit. I never noticed that the brand name is Clear Hooters until now. Pretty amusing. Thanks for all the help and advice. I owe you all a beer.