Monday, March 16, 2015

On Re-Wiring An MGB Cockpit

My project car, the old Time Eater, a 1973 MGB, still sits in my garage with the wiring incomplete. When I pulled the thing out of storage, I found that the old wiring harness had rotted away and needed to be completely replaced. Instead of buying a wiring harness, I decided to rewire the car from scratch myself so I could make some improvements to the system.

It turned out that getting the Chronovore back on the road wasn't as nearly as important to me as I had thought and weeks turned into months which turned into years. Confronted daily with the little guy in the garage, I tweeted this.
This weekend, I rewrote my goals (I try to do this every 6 months, but it's really more of an annual thing) and I put dates to the stages of my MGB restoration. For example, I'd like to have the cockpit done by this Sunday.

The issue here is that the wiring in the cockpit is complicated, the most complicated part of the car. Actually, now that I write this, it's only complicated where it comes out of the ignition, wiper and blinker switches on the steering wheel column. The rest is relatively straightforward. For example, coming off the ignition is the auxiliary power feed that goes to the wiper motor, the fan blower switch, the windshield washer pump and so on. Each individual light or instrument is fairly simple.

The problem comes in wrapping the wires. I've got most of the wiring in, running behind the dash and into the engine compartment where needed, but when I'm done, I'll need to pull it all out and wrap it with electrical tape. Further, feeding the lines behind the dash is quite a chore, something you can't do when the instruments are in the dash.

The magical piece here is sequencing the installation. What goes in first and what goes in next and so on? As I hinted above, I've not been very serious about this project, but now, since I've put a deadline on this, things just got real as the kids say.

I'm going to take a spiral notebook and make a single page for each switch and instrument. I'll draw out the lines for that device. Once that's finished, I'll have a complete list of the wires that go from the cockpit into the engine compartment. I'll run and wrap those, leaving plenty of slack for the instruments and switches with the wires dangling out of the dash where the devices go. I'll then attach the wires in the steering column since those can't be moved. Finally, I'll attach the instruments and switches, one at a time, from left to right in the cockpit because the exit into the engine compartment is on the right hand side.

That ought to do it. Making a single page for each circuit will also allow me to double-check my current loads. I've been using 18ga wire in most places, but I'm a little concerned about that. Every time I check amperage ratings, it looks good, but it just feels like I should be using larger wire.

There. A plan and a deadline. And now, on to victory!


tim eisele said...

"the wiper motor, the fan blower switch, the windshield washer pump"

Hey, you live in California. It's warm, so you don't need the blower for heat; it isn't sloppy, so you don't need to wash your windshield; and it evidently never rains anymore, so you don't even need the wipers. Just skip them all! That will simplify things.

All you really need is the lights and the ignition switch, right?

tim eisele said...

As far as the wire diameters go, is there really any need to keep it low? The heavier gauge isn't *that* much more expensive, and peace of mind is worth something, after all.

Unless the heavier gauge won't physically fit, of course.

Mostly Nothing said...

I hope you are using heavier wire for lights. By improvements, do you mean moepre fuses, relays for the lights, and more grounds?

Doing this will really put the D in DPO. Or are you going to end up giving it to a son?

K T Cat said...

Tim, sadly I need all of those features. In any case, they take almost no effort at all to wire up.

K T Cat said...

MN, I'm using relays in the engine compartment for the lights. I don't think anything else draws much current. That's one of the things I'm going to double check with my individual circuit drawings.

Mostly Nothing said...

The horn too. It makes a difference. I bought a kit from British wiring. Makes a difference. They do improved wire harnesses.

Oh, and instead of electrical tape, Moss has the blue covering for the harness.

K T Cat said...

Now you tell me! I taught myself to do the electrical tape wiring wrap and now that's what I use.

And, as you know quite well, I'm too old to teach new tricks.