Ammeter bypass questions

[Knebel]

I am going to attempt on the ammeter bypass soon, I have read the mad electric article about it where it says to connect the wires behind the dash and put both ends on the starter relay (to describe that simple).

I just have too much voltage loss when turning on the ignition to reliable feed my switched 12v sources. When I turn on the IGN, I see 11.8v on the switch and when the battery is already a little low, it dosent have enough juice on the IGN wire. I did troubleshoot a lot and it's not the IGN switch or the bulkhead... Another alternative would be using a relay and have the IGN engage that feeding battery power to my switched 12v junction. But that's just more and more wires I don't really want to add.

I already have a new 8ga charging wire from the alternator through a circuit breaker to the batt +. Would it work if unhook the ammeter, cut the wire where the welded splice is, take the whole "loop of wire between alternator and starter relay" out, then run an 8ga wire into the car, Connect it to the welded splice and the starter relay? All it needs is a hot wire to the splice, am I correct? Seems to me that would be the cleanest solution...

 

[saylor]

+1

i just ordered fusible links and whatnot today to do the exact same thing.

in addition to MAD, look at nachos parallel wiring. i think you are halfway in between each method with your question.

P.S. looks like heat gun + 307pc wiring terminal kit from HFT will be less than $20

lets try not to die !

- saylor

 

[saylor]

this guy!

An Error Has Occurred!

 

[saylor]

.

from b-bodies

It is simply not correct to say that the car will not pull any more amperage; the 100A alternator will be able to push more current into the battery whenever the battery is not at full charge, and the beefier alternator will tend to keep the system voltage higher under heavier loads (like with lights and blower on), and thus more current will indeed flow to the car's system loads. With the stock wiring, all the alternator output will go through one single bulkhead spade connection, which is the known weak point.

As a minimum upgrade, I would recommend running a, 8 or 10 gauge wire from the alternator output to the starter relay big stud. At least the battery charging current will mostly bypass the bulkhead connectors. Note that your ammeter will no longer correctly indicate battery charge/discharge.

Look here for a good diagram to help you understand this. The article around this diagram is very good reading.

Catalog

nm9stheham, Apr 19, 2015
#13

 

[Big_John]

Correct me if I'm wrong, but don't you have an EFI system with high pressure pump etc.?

With this type of add-on, your stock wiring system isn't going to come close to handling it. IMHO, the mods you are talking about aren't going to help you much, if at all. As you draw more current, the voltage drop through the wiring, connectors, and even the ignition switch, is going to increase dramatically.

If you have a switched 12v junction (I assume a busbar or similar), I think you would be way ahead of the game if you feed that directly from the battery and switched it on with a simple relay circuit. An $8 relay and a few feet of wiring and you're done.... Minimal voltage drop and less strain on the old system.

The MAD mod to run a wire from the alternator to the battery (via starter relay) is a very good one... and I've done it myself. IMHO, in this case, it's not gonna fix the problem.

 

[Big_John]

Here's something to play with that will help you figure out the voltage drop. You'll have to change the parameters to DC obviously and plug in your wire size. Figure 10 amps (?) for a fuel pump, possibly more on starting.

Voltage Drop Calculator

 

[Knebel]

Well, yeah, a buss bar is what I have. It has the "brown?" And "blue?" Connected to it coming from the IGN switch. On that buss bar is anything what has a switched 12v incl EFI, alarm, IGN coil and a relay for my low pressure pump. What weird to me is, that I have 12.6v at the battery, starter relay and an additional fuse box where I run fuses for the whole additional stuff. I have a seperate 10ga wire going from the starter relay through a 50amp circuit breaker into the car the ammeter.

Now, when I turn on the ign, my voltage drops to 11.8 or lower on the 10ga wire coming from the ammeter going to the inside fuse box and IGN switch. When I crank, it drops low to under 10v, sometimes so low that the EFI won't fire right. Same voltage then on my junction but my battery stays at its 12.6v.

Somwhere in the car is 1v lost when I turn the key but don't crank and I am trying to eliminate that. I'm thinking running a wire from the battery to a relay and just switching the relay with the wire coming from the IGN switch.

Edit: the voltage drop calculator appears to be right. 0.6v drop and that's not including connectors. So from 12.6 to 11.8... It just drops too low for the EFI when I crank.

 

[Big_John]

Well, yeah, a buss bar is what I have. It has the "brown?" And "blue?" Connected to it coming from the IGN switch. On that buss bar is anything what has a switched 12v incl EFI, alarm, IGN coil and a relay for my low pressure pump. What weird to me is, that I have 12.6v at the battery, starter relay and an additional fuse box where I run fuses for the whole additional stuff. I have a seperate 10ga wire going from the starter relay through a 50amp circuit breaker into the car the ammeter.

That ignition circuit is over loaded. You have to think about not only the wire size, you have to remember you are pushing current through an old ignition switch.

Now, when I turn on the ign, my voltage drops to 11.8 or lower on the 10ga wire coming from the ammeter going to the inside fuse box and IGN switch. When I crank, it drops low to under 10v, sometimes so low that the EFI won't fire right. Same voltage then on my junction but my battery stays at its 12.6v.

If your voltage at the battery is still high, there's no doubt you are losing voltage in the circuit. It might be worth doing some voltage drop tests with the wiring too. None of this stuff is like fine wine where it gets better with age.

Somwhere in the car is 1v lost when I turn the key but don't crank and I am trying to eliminate that. I'm thinking running a wire from the battery to a relay and just switching the relay with the wire coming from the IGN switch.

Yep... That would be the way I would do it.

 

[saylor]

hey knebel!

you need another 10ga wire from amm blk post to ALT

that may be the problem is if you dont have that. you have only half of nachos recommended wiring

 

[saylor]

the 10ga wire you added already should be from starter relay to red post amm


so add 2 wires total, 1 red, 1 black

 

[Knebel]

I have the normal ammeter circuit but it just bypassed the bulkhead.

 

[Gerald Morris]

Check the resistance of your ignition switch. Try a contact cleaner spray on it and see if that helps. Even 2 10 ga wires in parallel don't have that much ampacity if modern current sucking devices get hooked to such a feed. Mathilda was already modified as per the Nacho fix when I got her, but after a nasty short which burned most of the current supply wires soon after, I re-wired a lot of that stuff, cutting the welded junction out and replacing the alternator feed with #8 to the battery w a fusible link. I don't like breakers on the main current carriers, as they have a way of tripping when any momentary demand over-current hits. Fusible links give better real protection, and the wire is cheap.

 

[Knebel]

Uh oh, I thought I had mentioned it but apperantly not. I put in a brand new ignition switch today, I also cleaned the connector but that didn't help. My IGN switch was a little wonky so I just replaced it but I can actually measure the voltage drop before the switch on the main wire from the ammeter.

 

[Gerald Morris]

Look for a short on stuff from the Acc side of the fusebox. Try disconnecting stuff, one at a atime ans see if your voltage @ the switch doesn't come up. Some shorts will just load the main circuit, esp if they're small, like nicked/cracked insulation on 50 yr old vinyl. Check your LIGHTING, and perhaps pull the instrument panel. I don't use mine, relying on bimetallic temp sender and mech oil pressure gauge w a simple voltmeter. Check the crappy instrument power supply in particular if present. Also, what sort of voltage regulator do you use with your EFI? That too is a potential source of low potential.

 

[Knebel]

I use a 70s regulator. Have no issues charging, when the car is running I get 14.5v everywhere. I just notice the drop while cranking or turning the IGN on and that messes with the efi

 

[Moparmat2000]

This should help. First schematic shows stock wiring, second shows bypassed ammeter. After that, convert the ammeter gage to volts

 

[Yatzee]

I am going to attempt on the ammeter bypass soon, I have read the mad electric article about it where it says to connect the wires behind the dash and put both ends on the starter relay (to describe that simple).

I just have too much voltage loss when turning on the ignition to reliable feed my switched 12v sources. When I turn on the IGN, I see 11.8v on the switch and when the battery is already a little low, it dosent have enough juice on the IGN wire. I did troubleshoot a lot and it's not the IGN switch or the bulkhead... Another alternative would be using a relay and have the IGN engage that feeding battery power to my switched 12v junction. But that's just more and more wires I don't really want to add.

I already have a new 8ga charging wire from the alternator through a circuit breaker to the batt +. Would it work if unhook the ammeter, cut the wire where the welded splice is, take the whole "loop of wire between alternator and starter relay" out, then run an 8ga wire into the car, Connect it to the welded splice and the starter relay? All it needs is a hot wire to the splice, am I correct? Seems to me that would be the cleanest solution...

The bare minimum you can do is to remove the two wires from the ammeter posts and join them together in a very solid manner- crimped bare bullets, soldered and covered with two layers of quality heat shrink. To improve on this even more ( one wire on the meter comes from the engine compartment the other goes to the fuse block)
replace the feed from the engine compartment with a new 10 ga feed directly from the battery post or positive battery terminal on the starter but instead of a lame fusible link, install a maxi or midi fuse holder rated at or about 35 amps. Bypass the bulkhead connector in a way that's not noticeable and use color coded wire for future reference. Trash the alt and outboard voltage regulator and upgrade to a newer, high amp alt with built in electronic regulator. You can purchase one that looks exactly like the original right down to the case. They are way more responsive to load demands than the old system and don't cause surges like the old style points-type regulators. Leave the old crap in place so things look authentic. The main feed fro the alt goes directly to the positive battery post or post on the starter and can be 10 ga as well and again should have a maxi/midi fuse somewhere in line. These fuse holders use a "ribbon" type fuse that is retained by two small nuts, the cases are small, black and have a cover. They are easy to conceal and look very inconspicuous. Rate your fuses 15% below the output rating of the alt or total draw from the fuse panel with everything on. An amp meter comes in handy here. Now you'll have a high output charging system, protection against surges and shorts on the primary circuits ( the fuse panel remains the same and protects secondary circuits) and no worries from a meltdown. I also highly recommend the use of a relay for the ignition circuit, taking the load off the ignition switch, but only one 30 amp rated relay is required. I say 30 amp because the internal contacts are more robust and not affected by arcing as much when the contacts open and close. If you add electric fans, fuel pump or EFI they will be on their own fused relay triggered by the ignition relay you previously installed. Do not attempt to use the existing fuse block to feed these new, higher load accessories, they must be installed and wired as a sub-circuit with their own fuses.

 

[Knebel]

Sounds good. It appears like I have done most of it.

I have add-ons fed from a seperate fusebox which is fed directly by battery. The add-ons are turned on by the IGN switch which has the wire connected to a junction, this junction has everything what required "switched 12v" on it. But no relay,just the power coming through the IGN switch.

So much for that...

The ammeter circuit:
I have a new 10ga wire going from the starter relay into a 40amp circuit breaker, then through the firewall (NOT BULKHEAD) to the ammeter, then from the ammeter it distributes as normal. Furthermore I have a 90amp alternator which has it's charging stud connected to a circuit breaker and then directly to battery positive.

My question is: the ammeter is in a loop between the alternator stud and the starter relay stud, correct? I want to get rid of this loop(if I just take out the ammeter and connect the wires, the loop is still there), mainly the additional wire from the alternator into the car. Taking off this wire, completely, and just have one 8ga or so going into the car connected to the splice which feeds everything. Then modify the ammeter to be a Voltmeter.

 

[Big_John]

Furthermore I have a 90amp alternator which has it's charging stud connected to a circuit breaker and then directly to battery positive.

My question is: the ammeter is in a loop between the alternator stud and the starter relay stud, correct? I want to get rid of this loop

It was until you did the mod in the quote above. By wiring directly to the battery, you've created a lower resistance path for the charging current from the alternator to charge the battery.

The amount of current through the dash wiring is just for accessories and ignition. You can bypass the ammeter if you want, it's not a bad idea and it's pretty much useless now anyway.

At the risk of repeating myself... What you need to do is relieve the amount of current passing through the dash and ignition switch is to put a relay or relays on your added EFI and related stuff. You can do all the rest of the MAD/Nacho etc. mods and still not do anything to help yourself. If the EFI is that sensitive to anything less than 12 volts, then you have to give it 12 volts and that requires a dedicated circuit.

 

[Gerald Morris]

Big WARNING about the "Nacho fix:" Big John RIGHTLY points out that by placing the OLD conductors from the battery and alternator in parallel, nearly ALL the current will take whichever conductor/path has lowest resistance. That was what compelled me to cut out the old welded splice, and just run #8 from the starter relay through the firewall, (via a hole w a rubber grommet) to the fusebox, IGN & lighting junction. I charge from my stock 60A alternator w a separate #8 to the battery, with that AND the #8 from the battery each protected by #12 fusible links, 6" long.

Big John's admonition is best. Feed your EFI via relays & a separate overcurrent protection from the battery. This way, squirrely voltage from the IGN sw will just be used to actuate the contactor in the relay, and the EFI will get what it needs.

These considerations just underscore my case against installing EFI, unless you're willing to wire it and a number of other circuits accordingly, you will cause yourself grief. I might, if I cop a really good score on price, go for a 1 wire alternator, as the venerable arrangement with the separate voltage regulator can cause trouble too.

You REALLY need to get that relay though. It will ELIMINATE the crap voltage. Check resistance to hot on each leg of the bypass loop, and voltage. I suspect your trouble is in that. Even a solid state regulator might be sending current to thge field coils of your alternator, and this, when you throw your IGN sw will cause a drop.