MAD Wiring with Autometer Voltmeter already installed

[jrcr_15]

Hello,
I have been reading and rereading the MAD article about upgrading your wiring system. I recently had an old alternator rebuilt and it now puts out 80 amps. Being that I have electric fuel pumps, fans and waterpump it is a no brainer to make some adjustments.

I have read the MAD article a few times about by passing the amp meter. Problem is that I already have a volt meter installed in my dash in its place a number of years ago, and the amp meter is long gone. I have been really trying to make sense of this with how my car is set up. Has anyone done this? I do not want to start ripping my dash apart and playing around with thing before I know 100% how to go about it.

Any pointers / diagrams would be appreciated. I have this volt meter if that helps:
2-5/8" VOLTMETER, 8-18V, AIR-CORE, SPORT-COMP

Thank you

 

[67Dart273]

The MAIN thing with the MAD mod is to reduce the current in the old ammeter circuit, as the alternator "used to go" From alternator.......charging wire.....IN THROUGH bulkhead BLACK.........(branch off to feed loads, welded splice) through ammeter.........BACK OUT bulkhead connector RED ........... and through fuse link............and back to battery

This is not necessarily "electron flow" this is the functional path

So what you want to do is to reduce the load through the bulkhead. If you turn the red and black into parallel supply paths AND ELIMINATE the battery charge path, then the current in the bulkhead is reduced dramatically

Therefore if you run a jumper from the alternator to the battery (starter relay) then the battery charge current will go direct to battery, and the two (RED and BLACK) bulkhead wires will now only supply current to feed interior loads in the passenger compartment

THE ONE THING you need to keep in mind with this is.........the fuse link is no longer a protector, and the alternator will not be fused, either. It would behoove you to put a large fuse / fuse link in the new charge wire, and to fuse the old black alternator wire as well

Catalog

Follow along above.........If you jumper from alternator to battery, not only is that path "not fused" but now the black charge lead runs into the car and supplies power into the car "along with the red". The RED is still fuse link protected, but if there's a jumper, neither it nor the black charge wire are now fused, NOR ARE ANY OF THE LOADS coming off the welded splice

 

[SB69GTS]

Can he leave the existing Black/Red wire that feeds the fuse box/light switch/ignition ...and just run a heavier red wire from the alternator to the battery with a appropriate fuse or breaker just before the battery.

 

[67Dart273]

Can he leave the existing Black/Red wire that feeds the fuse box/light switch/ignition ...and just run a heavier red wire from the alternator to the battery with a appropriate fuse or breaker just before the battery.

As I eluded to above, your old black charge wire is now a supply wire and IS NOT now fused. So you should, depending on wire routing, fuse it

 

[jrcr_15]

As I eluded to above, your old black charge wire is now a supply wire and IS NOT now fused. So you should, depending on wire routing, fuse it

Thank you very much for your help and insight on this. I have read into this using an old service manual that my dad had and other things around the web.

I am more of a visual person, and I modified the photo above to what I believe you were alluding to. Does this make sense in my case? I will put a FL on the black wire going into the car, and put solid wires thru the bulkhead as an alternative to the factory plugs.

Sorry for sounding dumb. My dad was the brains of this build I have going and he unfortunately passed away a month ago. So I am researching the crap out of everything.

Please let me know if there is anything I missed.
Thank you again

 

[67Dart273]

Sorry to hear. I lost mine in '95. he was only 71

 

[mopowers]

Can he leave the existing Black/Red wire that feeds the fuse box/light switch/ignition ...and just run a heavier red wire from the alternator to the battery with a appropriate fuse or breaker just before the battery.

A few really bright people on this website recommend doing that.

 

[jrcr_15]

A few really bright people on this website recommend doing that.

Thanks for your input. Does this diagram make sense to what you are referring to?

If so, what gauge wire do you feel is best to run from the alternator to the battery? Also, what fuse?

 

[mopowers]

Thanks for your input. Does this diagram make sense to what you are referring to?

If so, what gauge wire do you feel is best to run from the alternator to the battery? Also, what fuse?

View attachment 1715081693

I'm far from an electrical expert, but I would think that would work very well. As far as wire size, it really depends on what alternator you're running. I would think a 12ga wire with 14ga fusible link would work fine with a stock-type alternator. Or step it up a size and go 10 w/ 12g fusible link.

 

[67Dart273]

EDIT.........didn't see your added link LOL

Here's the thing: You need to think about a big main fuse, and if you simply bypass as in the last diagram, you eliminate that by means of the black alternator wire now being a "hot feed." So add another link/ fuse etc

 

[RedFish]

Thanks for your input. Does this diagram make sense to what you are referring to?

If so, what gauge wire do you feel is best to run from the alternator to the battery? Also, what fuse?

View attachment 1715081693

In that drawing the volt gauge looks to be hot at all times. That would drain the battery. A volt gauge goes on a switched hot.

 

[crackedback]

The black alt wire is hot all the time anyways... Isn't a switch anywhere in site, just the welded splice.

I sell my bypass cables and tell people to leave everything OEM in place if the bulkhead is in good condition. No need to reinvent the wheel to feed the interior/fuse block. If you want to fuse the alt charge line, make sure it sufficient to carry a full load.

 

[67Dart273]

Yeh but it is not supplied FROM the battery, so if the engine dies, it's on the "other end."

 

[jrcr_15]

EDIT.........didn't see your added link LOL

Here's the thing: You need to think about a big main fuse, and if you simply bypass as in the last diagram, you eliminate that by means of the black alternator wire now being a "hot feed." So add another link/ fuse etc

Fantastic. I have it figured out now. Essentially when the VM was originally installed the amp bypass was already done. I just need to add in a larger gauge wire now. i am thinking that I will go with a fuse instead of the link. What size fuse do you think would be best? I am using 8 gauge wire as the new alternator puts out about 80 amps..