Underhood Ammeter Bypass

Thanks for the write-up on this cbarge. It was well done and perfect for newbies and guys that are fearful of electrical issues.

Getting that circuit in should be as priority as replacing wheel cylinders on these cars
..or going from single to dual master cylinder. It's not a matter of changing the originality... It a matter of safety and preserving your investment for the longhaul. These parts are 50+ years old, and like us...not getting any younger.

This should be a locked post and added to a mod/sticky so it doesn't get lost or have to be bumped

Thanks again!
 
There is a service bulletin somewhere on this site (or maybe I have a copy stored somewhere) That was the Chrysler approved method of the bulkhead connector bypass.
It has been a few years ago but seems like something @Big_John ? May have posted. Or was in the Hamtramck archives?
 
Turboomni said:
May I ask why a fusible link and could you just use a fuse? Thanks for this as I think even I could do this!
Click to expand...
The reason for a fusible link over a fuse is because the link will take a high current spike for a short time whereas a fuse will blow immediately. If you could find a "slo-blow" fuse it would be closer to what the fusible link provides. IMO, a circuit breaker would provide a better protection than a fuse since they too will take a short term spike in current. I use the fusible link because that is what the Mopar engineers thought was best for the money.
 
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Thanks for the pictures, write-up, and links, everybody! Seems like some of the mid-80s IROC-Z Camaros used a dual fusible link, in parallel? They typically had 100A plus alternators by that time. Using quality, OEM-spec terminals and such would be important, I suspect, to ensure the least resistance in those solderless connectors, I suspect.

THANKS cbarge and HWYCRZR for making it simple for us!

CBODY67
 
I did this the other day. Honestly should've done it when I first bought the car. Of I had we wouldn't have taken a 206 mile rollback ride home from Carlisle. Sure was glad for AAA, cost me $24.

I spent more time messing with an old woren out firewall harness clip than the wiring. I used black white and place a small piece of red breast shrink on the end so it would hide better. I also used a fusible link, 10' was like $4.
 
The Captain said:
I have done this numerous times and the ammeter works but reads backwards.
Click to expand...
I have done this mod, and I really like getting a significant amount of current flow out of the bulkhead connector (and the ammeter). My meter reads "slightly discharged" from the middle marker while everything is working properly under minimal load, and this is the New Normal for that meter (and yes, is slightly annoying). Turn on blower or headlights and the meter shows an alarming amount of discharge, but this is simply the same amount of discharge movement that you would see from the middle marker if you hadn't made this mod. When the car is off, the meter settles back to the middle mark. Also, I used black 10 guage wire so everything looks OEM, and soldered the connections for permanent and perfect conductivity, including the fusible link. I'm not a big fan of large crimps.

I have also powered my AC clutch via a relay (tucked away and invisible under the receiver dryer, all wiring looks normal), powered from the alternator stud and triggered by the pressure switch wiring. This has taken another 5-6 amps out of the bulkhead connector AND doesn't show up on the ammeter, since it's all on the battery side of the electrics and not through the meter anymore.
 
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Trace 300 Hurst said:
I have done this mod, and really like getting a significant amount of current flow out of the bulkhead connector (and the ammeter). My meter reads "slightly discharged" from the middle marker while everything is working properly under minimal load, and this is the New Normal for that meter (and yes, is slightly annoying). Turn on blower or headlights and the meter shows an alarming amount of discharge, but this is simply the same amount of discharge movement that you would see from the middle marker if you hadn't made this mod. When the car is off, the meter settles back to the middle mark. Also, I used black 10 guage wire so everything looks OEM, and soldered the connections for permanent and perfect conductivity, including the fusible link. I'm not a big fan of large crimps.

I have also powered my AC clutch via a relay (tucked away and invisible under the receiver dryer, all wiring looks normal), powered from the alternator stud and triggered by the pressure switch wiring. This has taken another 5-6 amps out of the bulkhead connector AND doesn't show up on the ammeter, since it's all on the battery side of the electrics and not through the meter anymore.
Click to expand...
If you didn't run the blower motor off a relay that's another crucial one. I saw a 2 volt drop in the cabin voltage when running
ac on oem wiring. I ran the high fan position as trigger to relay and got full voltage back in the cabin to the other devices.
 
Great thread, never knew about any of this - very important to keep the smoke inside the wires! I agree it should be a sticky.
 
furious70 said:
If you didn't run the blower motor off a relay that's another crucial one. I saw a 2 volt drop in the cabin voltage when running
ac on oem wiring. I ran the high fan position as trigger to relay and got full voltage back in the cabin to the other devices.
Click to expand...

I agree it's crucial, and thankfully my brand new fan doesn't have the huge current draw (and slow speeds) that my original did. I'm glad you mentioned this, because I've thunked about how to have a relay with the three fan speeds. So are you saying you only run the fan on high, or only have a relay for high, with the low and medium speeds at normal current draw? I guess three relays for the three resistor coils, maybe? I need the lower speeds because the 40* air out of the center vent can make for a nipply ride. :wideyed:

If you do a How To, I'll do one for my AC clutch relay. :thumbsup:
 
Many later '70s GM a/c systems have a "high blower relay", just for the "high" fan speed position. The lower speeds are direct-wired via the blower resistor item.

CBODY67
 
I did it only for high speed since I always use high in that car. Even now with a new blower motor and the relay I don't have the wind I'd like.
I should have taken photos back when I did it. The wiring in my car is not oem anymore though with the alterations for 1wire alt and efi
 
Sixpactogo said:
The reason for a fusible link over a fuse is because the link will take a high current spike for a short time whereas a fuse will blow immediately. If you could find a "slo-blow" fuse it would be closer to what the fusible link provides. IMO, a circuit breaker would provide a better protection than a fuse since they too will take a short term spike in current. I use the fusible link because that is what the Mopar engineers thought was best for the money.
Click to expand...

If one was to choose a circuit breaker for this bypass, how many amps circuit breaker would be recommendable?
 
I've been working on my gauge cluster in my 65 SF. I've decided I'm going all in and gut the whole circuit to the Ammeter including the meter itself.

Rather than do the bulkhead drill out, I'm going to use an existing grommeted hole that was cut in to wire the electric fan that was installed in my car.

The Ammeter will be swapped with a custom fitting volt gauge, and use the original ammeter face place.

The bypass works great, but being able to cut out old wire and run new direct to the source/demand makes even more sense.
 
Leaburn will detail the bulkhead bypass. Like James above says, bypassing the unsafe high current flow bulkhead connection(s) is a VERY good idea.

Interestingly, my Monaco had it done at the factory as part of its "police" pedigree. While it's just the main feed to the amp gauge, it takes a lot of constant load out of the bulkhead. Other things like AC, fan, etc are still running through there, but as their use is intermittent the logic is they're less failure prone.
 
well thanks for this. It makes me think about my charging situation. I've bypassed the ammeter under the dash and I have relays to the battery to most of the high load things like headlights. My concern now I guess is going to be the electric fans. They pull over 25 amps continuous and spike to 40 when they spark up. With the fans and the headlights, I don't think the alternator would be able to keep up. oy.
 
I'm running an electric fan, single 22" wide. Runs fine, even with headlights on.

I'm adding a tach and a stereo system pretty soon. Not sure how big I'll go with the radio, as I'm thinking I'll be maxing out the Alt.
 
I am running a 95amp "Roundback" Powermaster alternator. Part # 7018
Looks factory but packs a punch,LOL.
My car originally came with 38 amp alternator.
I did use heavier wiring,bypassed the bulkhead and did the underhood bypass as well.
Also running an electronic voltage regulator.
No issues.
The plan was if I ever was to go with a big stereo or add A/C and electric fans the car is readily capable to handle the electrical load.
DSC01748.JPG
 
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