Brain Fade (part 2)

Danny - Allow a few questions, please. When you say power is present at the back of the fuse box, could you be more descriptive? Are you stating that there is voltage on the input side of the fuses? What about power at the junction block on the main fuse/relay board? The large red wire coming off of the battery (not to the starter but to the system bus) first goes to the amp meter, then to the junction block on the fuse/relay board. The junction block has 4 screw-down terminals with approximately 6 wires attached. Is there power to this junction block? It is from there that power is distributed to the fuse array and the remainder of the car.

Are you sure that the battery terminals are tight without corrosion? You might entertain simply loosening them and twisting the connector, and then retightening. The contact resistance may be high and this can act like no power.

The clock does not work? (Low current draw - likely to work even if everything else does not).

Jim S.

 

Problem may be at the amp meter or on the back of the ignition switch. If you have power at the junction block, and nothing beyond that, then the main red wire going to the ignition key, or the large red wire going to the amp meter may have come loose. I do not fully understand where power is. Even with the ignition key off, there will be voltage applied to several of the fuses. If you are saying that all of the fuses have voltage when the ignition key is on, then you have entered the Twilight Zone. Makes no sense. If you are suggesting that there is no power to the fuses, then all is well and there is simply a single point of failure, either going to the key or the amp meter.

It is possible that the ignition key switch has failed. Easy to bypass for a test. Remove the large red wire and touch it to the large blue wire. This should power up many of the loads (lights, etc.).

Jim S.

 

Greetings, Danny.

I don't recall if your car is a show car or a driver, but this might be the opportunity to consider a Veglia volt meter in place of the amp gauge. greg246, in Sydney, referred to the 'proper appearing' (see picture, post script) item available from Dino Parts in Germany.

http://www.dinoparts.de/content.php?sID=a3732b679288a760e43f5dd60faf81bf&tpl=shop&mode=details&mID=-5&fID=2&kID=222&pID=214&cur=EUR&lng=en&page=1

There have been several threads that discussed the pros & cons of swapping out the potentially hazardous amp gauge for a relatively benign volt meter.

'funny that Maranello brought up this same issue in August.

http://www.ferrarichat.com/forum/showthread.php?t=210122&highlight=volt

Maranello...how'd it work out?

I'm no electro-wizard, Danny, but we have several on the forum. What do you guys think about the swap?

Coop
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Danny,
The Ampmeter is directly in line with the battery, meter, big fuse on firewall and alternator. All overcurrents are supposed to be handled by the fuse and the ampmeter is supposed to be protected. Check what kind of fuse your man installed and check that the big fuse is there and not jumped. There are cases of the terminals on the back of the meter coming loose. The resulting heat destroys the meter without blowing the fuse. No telling what happened with the reversed battery. You don't need an extra fuse rated at 50-60 amps.

An ampmeter is a better instrument for diagnosing faults than a voltmeter. Get it fixed or replaced.
John

 

John, as always, has it right. I have experienced the dreaded amp-toaster, although I caught it in time to prevent damage.

ALL DINO OWNERS SHOULD PAY ATTENTION TO THIS. Over time or as a result of removing the instrument panel periodically for restoration purposes, the brass nuts holding the high-current lines to the amp meter may loosen. You now have a very expensive toaster. Approximately 40 amps will flow through these lines (at various times), and if the contact resistance is greater than a fraction of an Ohm, heat will build.

It is prudent to periodically examine and tighten these 8 mm nuts. It is best to disconnect the battery, remove the amp meter, use steel wool to twist around the threaded stud, clean well, and retighten the nuts taking care not to strip them. Make sure to steel wool or sandpaper the ring connectors as well.

This is not an overcurrent situation, but a consequence of normal operating current passing through aged contacts. Damage to the amp meter or fire under the instrument panel may result.

Jim S.

 

Danny - thanks for the comment. Just to quantify the physics of the process, and perhaps to make the point more vividly, allow me to do a simple calculation.

Your toaster is typically 1 kilowatt heat source, that is, the glowing red wire is generating 1 kilowatt of heat, which is converted from electricity.

The relationship between electrical current and heat energy is (current * current) multiplied by resistance. In the vernacular of electrical engineers, this is pronounced I squared R heat. It is the square of the current multiplied by the resistance.

If your amp meter contact had deteriorated to 1 Ohm of resistance, with 40 amps flowing, the I squared R heat generated willl be 1600 Watts !!!! Take out the coffee, bisquits and jam, we are going to toast our breakfast, or better yet, the marshmellows and Graham crackers, cause we're going to have a barbeque.

Jim S.