Bulkhead Connector Bypass Step by Step

Post by **MattH** » Wed Sep 23, 15 1:15 pm

Thats a neat install Dave.

Post by **MattH** » Tue Sep 29, 15 9:59 am

Just started working through this.

I have added the thick cable straight from alternator to starter relay post (battery) so that the charge is now going straight there.
I have also bypassed the ammeter, using Demon James suggestion of just moving both connections to the same side of the gauge. Seems ideal as it is bypassing the meter and providing a good solid bolted connection, rather than trying to cut and splice or solder the two together whilst lying under the dash board.

What I haven't done is to bypass the bulkhead connector.

My thoughts are that despite all the problems these are renowned for, mine does not look to have ever overheated or caused issues with things not working.
Now that I have put a large wire straight to the battery from the alternator, surely the bulkhead connector wiring is drawing alot less current and is less likely to have any overheating issues?

It also means that I havent had to cut any wires at all, I have left the original alternator wire in place so the loop of power wire for everything else is original but is not having to deal with the alternator charging as well.
I assume with my limited electrical expertise that the larger wire will take most of the charging current as the charge will go via the path of least resistance.
I have noticed straight away that the dash warning lights don't now dim with the engine revs, so I think all is well, and better than before.

This might seem like only doing half a job, but I was wary of cutting and joining wires when everything works, and having reduced the loading through the bulkhead connector (which has lasted 42 years) I am hopeful it will be Ok running at reduced current.

I do plan to install relays for the headlights as well, but that is a seperate job.

I welcome views on this. Although I havent done the full suggested bypass, I think I have alleviated a major issue ( I was getting poor charging as the crimp conector at the alternator was crusty), bypassed the potentially flammable ammeter, and not had to cut and join anything, just make up one new wire,(thanks for the heat shrink James

) and move one connection onto another.

Dave999 · Post by **Dave999** » Tue Sep 29, 15 10:28 am

all that goes through the bulkhead now is what you are using

rather than what you are using and what the battery needs to charge, which could be 20 amps if its flat

Dave

Post by **MattH** » Tue Sep 29, 15 10:51 am

Thats what I thought so I hope with the reduced load it will stay unmelted !

XP29 · Post by **XP29** » Tue Sep 29, 15 8:56 pm

I need to get my head round the bulkhead connector in our car. From what I think I understand the ammeter in my cluster has a points style thing which limits the power going to fuel/water/oil gauges to 5v. If this fails then 12v goes to them which spikes them and kills them. This must have happened in ours as the oil and water are disconnected (presumed dead) and the points style thingy has been replaced with a more modern reliable unit.

The one thing I'm not sure about is if I reroute the charging circuit so it misses the bulkhead is if I will not have a working fuel gauge?

Post by **MattH** » Wed Sep 30, 15 7:58 am

XP29 wrote:
The one thing I'm not sure about is if I reroute the charging circuit so it misses the bulkhead is if I will not have a working fuel gauge?

This is why I left the original wire in place as well. The original system takes the charging circuit through the bulkhead and everything from the car is fed off that. I have left that as a feed to everything else but put the extra, thicker cable in to take the charge direct to the battery.

Steve's excellent description, and the MAD article show how the feed loop can be run direct from the starter relay terminal to feed everything.
I found it helped to study the wiring diagrams on the MAD webpage, they are clear and simple and show the before and after.

XP29 · Post by **XP29** » Wed Sep 30, 15 5:08 pm

Ok cheers, I'll check them out. Need to read a few times for it to sink in

drewcrane · Post by **drewcrane** » Thu Feb 18, 16 3:46 pm

I HAVE THIS BOOK MARKED EXCELLENT THREAD

XP29 · Post by **XP29** » Sun Jun 26, 16 10:10 am

What size cable is needed from the alternator to starter relay? Think in Steves post he's used 35A cable? The 65/30? Does it not have to be rated 70A if that's what the alt is putting out?

Pete · Post by **Pete** » Sun Jun 26, 16 11:30 am

I have put 70A cable on my Alternator.

XP29 · Post by **XP29** » Sun Jun 26, 16 11:44 am

Cheers Pete, so would that be about a 4 gauge wire (about 6mm)?

The one in the car going to the melting connector looks tiny, I'm guessing about a 2.5mm. I'm not that clever with car electrics, how does the power output of an alternator work? I'm presuming it's not putting 70A out all the time?

Pete · Post by **Pete** » Sun Jun 26, 16 1:09 pm

10mm CSA.

XP29 · Post by **XP29** » Sun Jun 26, 16 2:36 pm

Cheers Pete.

So if I run a suitable cable from alternator to the poz terminal on starter relay. Then a cable from same connection into car to pick up under dash connections an back again while connecting the two ammeter connections together. Do I have to have the fuse able links on the connections at the starter relay? What would happen if I just connect the cables straight on?

Blue · Post by **Blue** » Sun Jun 26, 16 5:20 pm

To be on the safe side you should always fit a large enough cable to handle the max output of the alternator. You are right, the alternator output totally depends upon the load you put on it. You have to drag output out of it if you like. Think of it this way, the battery is only there to start the engine, once running any electrical demand will be supplied by the alternator, the more you switch on the harder it works.

XP29 · Post by **XP29** » Sun Jun 26, 16 6:32 pm

Thing I'm not sure about is the fuseable links at the starter relay? Are they needed? I've seen one thing that had fuse links on each cable going back, another had it just on the alternator cable, I'm guessing here but presuming MattH above who just ran a cable from the alternator didn't put a fuse link in?