Bypassing red wire at bulkhead connector

[Alexander D.]

I've had intermittent loss of power on my '67 coupe due to the dreaded "red wire" problem. This is most disconcerting when traveling at speed and suddenly everything in the car dies, including the engine!

Wriggling the inboard bulkhead connector restores electrical power. However, that is only until the connection wriggles loose, leaving me dead on the road once again.

So, I've decided to install a bypass wire to get around the troublesome bulkhead connection.

Folks who have bypassed the red wire describe various ways of doing it. All involve some variation of running a parallel #10 G wire from either the hot post on the alternator or from the horn relay at the radiator, routed thru the firewall to connect to either the BAT terminal on the headlight motor relay (behind drivers kick panel), or directly behind the fuse panel (requiring removal of fuse panel). Alternately, the wire can be plugged into the power window terminal on the front of the fuse panel.

Of course the proper fix is to replace the wiring harness including the bulkhead connector. My car has a replacement engine harness from M & H, installed about 20 years ago. I don't want to replace the harness if I don't have to because everything else electrical on car works just fine.

My question: Instead of running a long bypass wire from the alternator and/or horn relay, is there any reason I can't splice into the existing red wire just before it goes into the bulkhead connector? From here the bypass wire would go thru the firewall to the BAT terminal on the headlight motor relay.

Splicing the bypass wire next to the bulkhead connector would keep the existing #10 red wire in the harness intact, including the fusible link that connects it to the horn relay. Doing the splice here would use the existing red wire and fusible link, so the bypass circuit would remain protected, obviating the need to install an inline 30amp fuse as recommended by some.

Here's the red wire going into the bulkhead connector in my car. I've removed the black tape to expose this bundle of wires from the harness. My idea is to cut the old red wire where it goes into the bulkhead connector, then splice the bypass wire to the red wire in the harness originating at the horn relay:

bulkhead connector.jpg/

My questions:

Is it viable to splice the bypass wire by cutting the existing red wire at the bulkhead connector and then splicing the new wire to the remaining original red wire that runs back to the horn relay? Once spliced I will re-wrap the bundle of wires going into the bulkhead connector to keep moisture out and also to conceal the bypass wire.

Or, is it preferrable to run the bypass red wire from the horn relay? If so, why is this preferrable? Also, can you confirm which terminal the new bypass wire should be connected to?

Here's a picture of my horn relay wiring:

Horn relay wiring.jpg

(The extra red wire with inline fuse goes to the blower motor on my factory A/C car.)

Is the wire with fusible link connected to the inboard (right) terminal on the horn relay the 'red wire' that feeds the cabin?

If running the bypass wire from the horn relay, should this new wire be connected to the left or right (inboard) terminal on the horn relay?

Is it a good idea to disconnect the original red wire w/fusible link once the bypass wire is installed, with an inline 30 amp fuse to protect it?

Thanks for sharing your knowledge on how to install a red wire bypass!

-Alex

[Marco H.]

Re: Bypassing red wire at bulkhead connector

Alex,

It seems that you have a fair amount of views on your topic, yet no one wants to take a stab at it. First, I'm not a fan of bandaging issues by going around the problem, instead of solving it.

To that point, the bulkhead connectors are very sensitive to have their interlocking contacts completely straight, otherwise they tend to push out, leading to intermittent contact. The reproduction harnesses have a tendency to cause issues, if the installer doesn't pay close attention to each pin engaging properly.

I suggest to inspect both pins for the red lead, see if one is recessed. If so, you may be able to fix it by reversing the retaining tab on the pin, which holds it in the connector (in some cases the tab is broken off, where the pin would need to be replaced). At that point, the opposing pin needs to be straightened, so it will no longer push its mate out of place.) Also, inspect the pins for oxidation; clean as needed. I use white lithium grease at the connector, as it will help keeping moisture out.

If you decide to run a wire instead, the AIM schematics in UPC12 should answer most of your questions. An inline fuse on a non-factory addition is always a good idea.

Hope this helps.
Marco

[Alexander D.]

Re: Bypassing red wire at bulkhead connector

Hi Marco,

I agree that ideally I would dig into the bulkhead connector to solve the problem. Howver, I'm a bit 'shy' about doing that because I've read and heard enough stories about connector tabs breaking off and/or difficulties with fixing the contacts in the connector. If I break a tab then the repair becomes rather more complicated and costly. So, I'll install the bypass wire and hope for the best. Cheers, Alex.

[Duke W.]

Re: Bypassing red wire at bulkhead connector

Alex,

I use white lithium grease at the connector, as it will help keeping moisture out.

Marco

White lithium is fine for door and hood latches that you regularly clean and lubricate, but it dries out rapidly and leaves the solids that can be difficult to clean out.

I use WD-40 on low voltage connectors. The water repellant film it leaves behind lasts for may years, even in the open air.

I agree fully with the advice to fix the problem at its root cause, which is most likely at the connector rather than resorting to a Mickey Mouse bubba fix.

Duke