MAD ammeter bypass question
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Thank You. Very informing video!
As far as removing the original charge wire from the alt stud while utilizing a shunt to the relay stud.........
This would appear to remove the parallel fusible link issue as it pertains to an under dash short while still keeping the charge load under the hood. In the event of an under dash short, the original fusible link from the batt. would work as designed would it not?
Other than the ammeter not registering, is there any other downside to this set up assuming that the removed original charge wire is well insulated?
72RoadRunnerGTX
Active Member
The battery charging current is not really the biggest load concern, with a fully charged battery there will be little to no charging current. On a weak battery any charging current is short term, unlike vehicle loads. With the original alternator feed disconnected, yes, the parallel fusible link circuit protection concern is alleviated but now you have all stock vehicle loads back on one Packard terminal in the bulkhead connector at the battery feed. Better to by-pass both charge path bulkhead terminals (fleet by-pass) and leave the ammeter alone after verifying the ammeter terminals are tight and there is no previous terminal/insulator abuse. Short of the fleet by-pass, the C-body recall would be a better approach to weak charge path bulkhead terminals than this “shunt wire” by-pass, retains the designed circuit protection and leaves the ammeter to function as it was designed.
72RoadRunnerGTX
Active Member
Show/describe it about half way through that video.
72RoadRunnerGTX
Active Member
Yep. Not sure where the 7.5 amp number you are using comes from. The single stock 6” 16ga fusible link should open with prolonged exposure to around 30-40 amps or so with a dead short in any of the stock unfused wiring or components. Parallelling the stock fusible 16ga link with another 14-12 ga fusible link (50-60amps to open) means it will take close to 100 amps to open both fusible links and stop current flow. Look up Kirchhoff's current law and the current divider rule. Using rough numbers here, exact numbers depend on just what the voltage drop ends up being across both legs of the parallel circuit from the point of the short circuit. Either way, the stock 12ga wiring won’t take anywhere near that kind of current, effectively no circuit protection at all, may as well not have any circuit protection on the shunt wire, wires will still burn.
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Working my way through your videos now.
I’m electrically retarded to it takes several times of watching or reading before I start to get it.
Mattax
Just the facts, ma'am
I basically agree. But will say that the main purpose of the fusible links is to deal with the battery dead shorting. The battery will flow well over 40 amps when dead shorted. Heck, people can and have arc welded using a battery!
The ignition run wire (J2) from the key switch is usually 16 gage. People should not be expecting fuselike protection in that circuit. If it shorts, then engine stops running and the alternator rotor stops getting fed so either way its going to shut down. I suspect that's why the manufacturers focused on the battery dead short as the main thing to be concerned about with respect to the main feeds.
The ignition run wire (J2) from the key switch is usually 16 gage. People should not be expecting fuselike protection in that circuit. If it shorts, then engine stops running and the alternator rotor stops getting fed so either way its going to shut down. I suspect that's why the manufacturers focused on the battery dead short as the main thing to be concerned about with respect to the main feeds.
72RoadRunnerGTX
Active Member
But? Indeed, as mentioned numerous times in my postings on this subject, the battery is the only power source with enough current potential (couple hundred amps plus) to burn wires, the fusible link protects the stock unfused wiring from the battery in a dead short event. While a short in ignition 1 may stall the motor while in operation, this won’t prevent its wires from lighting up was well, also only protected from the battery’s current potential by the fusible link.
Mattax
Just the facts, ma'am
Agree.
My point was that folks should not expect a fusible link to provide protection from extended periods of 40 amp currents.
The link may eventually open, but regardless, there will be damage to the weakest portions of the circuit.
The best protection is understanding what the ammeter is indicating and then taking an appropriate action.
My point was that folks should not expect a fusible link to provide protection from extended periods of 40 amp currents.
The link may eventually open, but regardless, there will be damage to the weakest portions of the circuit.
The best protection is understanding what the ammeter is indicating and then taking an appropriate action.
72RoadRunnerGTX
Active Member
True, and running a parallel wire run around the stock fusible link, even with its own fusible link, will remove any possible chance to avoid said wire damage in the event of a short anywhere in the stock unfused wiring.
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Mattax
Just the facts, ma'am
Connecting the parallel feed to the fusebox hot buss is a clever solution.
More so if the buss has an extra terminal on it as I've seen on at least some. (On the wrong 'puter to check my photos)
72RoadRunnerGTX
Active Member
’70-74 E, ’71-74 B, and early seventies C bodies have a BATT, and ACC, tap right on the front of the fuse box. Most have an extra male spade type piggy backed on the rear of the battery bus feed at the fuse box as well. Other platforms generally will have them too.
Excellent conversation fellas.
Mattax
Just the facts, ma'am
Most of the 60's and first few years of the 70s the A body fusebox has a fusebox like this. Both the constant hot (Q1)and switched Accessory (Q2) feeds connect to busses with an extra terminal.
Top view of a standard '67 fusebox with cover off.
That second terminal on the switched accessory buss was used by the factory to add a fuse for optional accessories such as tachometer and/or air conditioner (yes I know very different loads, but thats what was done). Here's an example that a member here was working on.
As I mentioned in an earlier post, the most common heavy duty factory wiring we see on the FABO is on cars with rear window defrost grids.* Those use ring terminals on the ammeter stud as a junction. I do not recall if anyone has posted photos of a fleet optioned A-body, although the wiring diagram shows in some of the service manuals and hookups are shown on a 67-69 assembly drawing.
In any event the fusebox buss is often easier to access.
*Links to examples from 73, 74, and a '75 here
Top view of a standard '67 fusebox with cover off.
That second terminal on the switched accessory buss was used by the factory to add a fuse for optional accessories such as tachometer and/or air conditioner (yes I know very different loads, but thats what was done). Here's an example that a member here was working on.
As I mentioned in an earlier post, the most common heavy duty factory wiring we see on the FABO is on cars with rear window defrost grids.* Those use ring terminals on the ammeter stud as a junction. I do not recall if anyone has posted photos of a fleet optioned A-body, although the wiring diagram shows in some of the service manuals and hookups are shown on a 67-69 assembly drawing.
In any event the fusebox buss is often easier to access.
*Links to examples from 73, 74, and a '75 here
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I started looking at the headlight relays. I see people have used the Toyota headlight assembly kit - 2 headlights and a harness with relays....$31 Cdn! The parts guy at Toyota even told me what a steal of a deal it was. I ordered one so we'll see what it looks like:
Genuine Toyota headlight kit made in Japan that works with the FJ60 and BJ60 Toyota Land Cruisers. This kit allows you to replace your sealed beam headlights with halogen headlights with replaceable bulbs. Kit includes:
- Pair of Headlamp Glass Lens
- With Bulbs
- Wiring Harness
- Zip Ties
- Instructions
OEM; Made in Japan.
Genuine Toyota headlight kit made in Japan that works with the FJ60 and BJ60 Toyota Land Cruisers. This kit allows you to replace your sealed beam headlights with halogen headlights with replaceable bulbs. Kit includes:
- Pair of Headlamp Glass Lens
- With Bulbs
- Wiring Harness
- Zip Ties
- Instructions
OEM; Made in Japan.
72RoadRunnerGTX
Active Member
If those instructions tell you to connect the relay secondary power to the battery, disregard that and be sure to connect the relay secondary power feed to the alternator or somewhere on the alternator side of the ammeter.
I believe you will like it.
Can I get the part number please.
Here you go:
8111060P70 - Toyota Headlight assembly kit. Oem; made in japan | Toyota Parts Direct, London ON
8111060P70
8111060P70 - Toyota Headlight assembly kit. Oem; made in japan | Toyota Parts Direct, London ON
8111060P70
Ya treed me! lol
'Cuda_ragtop
Woulda, Shoulda, 'Cuda!
Thanks for the tip! Just ordered from a US Dealer. $16.49 USD $11 shipping. What a Deal!
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