MG Sports Cars

Ok, Fred - wiring the hazards to the turn signals makes perfect sense to me. I'd avoided that because when I asked the wiring harness support guy he said it can't be done that way -- I'm sure now, he meant "it can't be done that way using just the stuff supplied." So, i've played with the info you've provided for the past couple of days & have come up with the following -- I think it covers all the bases. Let me know if you see any mistakes. Assuming I have this right, I'll need to figure out which wires that I have already run can be re-purposed to legs on this vs. where I'll need to run new wire.

Barrie, the diagrams are just done in Microsoft PowerPoint. I'm sure there's a better tool, but it's what I knew how to use.




Edited 2 time(s). Last edit at 12/15/2010 03:14PM by rficalora.

Two things Rob.

The dash lights will work the way that you have them wired, but it's going to be hard to isolate the grounds on all of them. And if one of them grounds out you can't turn off the headlights.
A better plan would be to power them from the 87 on the park light relay and ground them at the dash.
The other issue is the park light switch. It's currently unfused and you have a relay anyway so lets use that.
Ground one side of the switch just like the headlight switch and run the other side to 86 on the park light relay.
This is going to give you in effect two headlight switches so we'll have to isolate the headlamp side.
Use a double pole switch (just like the hazzard switch) for the headlights.
Ground two poles and connect one of the remaining poles to the park relay and the other to the dimmer, just like before. This way the headlights will turn on the park lights but the parklights won't turn on the headlamps.
This isolation can be done with diodes as well but the switches are more reliable.
Have you thought about a dimmer for the dash lights?

Cheers
Fred

That all makes sense Fred. I've updated the diagram to reflect those changes. I ran the dash light ground back to the ground bus rather than just grounding to the dash itself, but I'm assuming that's effectively the same.

With respect to dimmer for dash lights -- well, I'd thought about it. I have 3 of the dash dimmer switches from '67ish (metal dash) B's. None work & I hadn't taken the time to figure out whether there's a smaller option. So, for now, I've simply run the dash light feed on the back of my dash to a spot where I plan to mount the switch when I find one & from there back to the dash lights. In the example below it'd get tied inbetween the park light relay's 87 & the dash lights. But picturing that on the diagram, I'm realizing that may mean my park lights would dim with the dash lights! I've read about 12V DPDT relays; is that the answer here -- swap the park lights relay for a DPTD relay to isolate the dash lights side from the park lights so the dash dimmer doesn't dim park lights? Or is there a better way?

Rob

Yep it all looks good.
No problem with the dash dimmer. It will work just fine between the 87 and the dash lights. The park lights will still get full power from 87.
Now just build yourself a nice little harness and your in business.
I like to wrap mine in black hockey tape.( I'm Canadian after all.) It sticks really well, its very flexible, it avoids that goofy zip tie look and it gives that vintage factory appearance.
Get yourself the best full compression crimpers that you can find (they look like vice grips) and step up for nylon insulated terminals not the hardware store pvc ones. Or better, non insulated ones and self sealing shrink tube.
If you aren't 100% confident in your crimps ( you should be able to pull on the terminal hard enough to break the wire) then soldering might be a better choice.
Loose poorly crimped terminals cause more problems than any thing else.
Buy a good quality wire. The higher the strand count the better. Insulation counts too, PVC is bottom of the barrel. Silicone, nylon etc. are far superior. I will often buy a wiring harness from the wreckers and strip it apart. This gets you a pretty good quality wire and gives a greater variety of colours to use.
The brits use a standard wiring colour guide based on seven base colours.
Black is for ground connections.
Green is for ign. powered accys like wipers radio etc.
White is engine ign. power.
Red is for sidelights and park lights.
Blue is headlights. a red tracer is low beam a white trace is high beam.
Purple is accys that use constant power such as the interior lights, horn etc.
Brown is main battery power, generally unfused.
The trace colours are very specific and there are lots of them. If your interested "fat bloke racing" has a complete listing.
Hope thats all helpfull

Cheers
Fred

Thanks again Fred. I must be some sort of sick-o because I'm actually having fun learning how this works!!

Now, one last question for you & everyone else... The tech support guy at the wiring harness company thinks I'm crazy for adding in all this complexity (and failure points). He's basically saying the relays have a higher probability of going bad & causing a failure than blowing the headlight power fuse.

What do ya'll think -- remembering I have to have at least one relay because I'm using a toggle switch for my headlights instead of regular headlight switch.

Rob, while I agree about the failure rate, the up side of using the relays is that the higher current loads are kept off the toggle switch. This isn't as big a problem with high current rated switches, but really helpful to those guys using the original Lucas switches.
At least a bad relay is a rather simple unplug and plug swap and easy to carry a spare for. Blown fuses are another matter and usually replacing the fuse only results in blowing another one until the problem is found.

Times two Bill.
Fred

Rob,

I realize I'm coming late to the party, and I should have commented earlier, but I hope late is better than never. I have one problem with your circuits:

By connecting your hazard flasher the way you did, if you should happen to leave the turn signals on at the same time, the hazard flasher circuit will back feed through the turn signal flasher, powering up all the "keyed" circuits in sync with the flasher. Back in '68 when hazard flashers were first introduced, this was a common problem on American cars. Is this a realistic concern? Consider the following scenario: You're driving along when you notice a strange noise, so you pull over to the side of the road to investigate. Being a good citizen, you use your turn signal to let others know what you are doing. You pull off the road, turn off the key, and the turn signals stop. Then, being the thoughtful person you are, you remember to turn on the hazard flasher, but you forgot to turn off the turn signals because they quit when you turned off the key. Now your gauges, radio, fuel pump, etc are all flicking on and off with the flasher. More than just an inconvenience, it may very well put more load on the hazard and turn signal wiring than it is designed to handle.

You will need to add a DPDT switch to the circuit to isolate the turn signals from the hazards. Maybe the attached will be of help. Note that the hazard switch is shown in the "hazards on" position.

Dan

True enough Dan, if you're using the old bimetal flasher.
The newer electronic flashers are "open" at rest and won't backfeed.
But...the wiring isn't done yet and the isolating switch is a very good idea.

Cheers
Fred

Good catch Dan!

I noticed I didn't include the turn or high beam indicators on the diagram. Turn indicators are easy. High beam seems like it needs to pick up ground coming off the dimmer & flash to pass. Ok to pick up power off the same headlight power feeding the Park Relay 30 & 85?

And, where's a good source for quality un-insulated terminals?



Edited 1 time(s). Last edit at 12/17/2010 12:13AM by rficalora.

Sorry about the indicators Rob, I just assumed that they would be wired in.
Wiring the high beam indicator the way you described will work just fine.
Up here I get my wiring supplies from an industrial electrical wholesaler.
The local auto suppliers only seem to carry that nifty chinese stuff.
Someone closer to your area can probably give you a good ref.
Cheers
Fred

You can get decent crimp terminals such as ring lugs from Digi-Key. You can get them in a strip rolled on a spool which is pretty handy.

JB

Let's branch this discussion into more general wiring topics -- I started the thread so I guess it's ok for me to hijack it, right?

First, I'd like to have just a few connectors between my dash & the rest of the harness -- to make it easy to remove the dash. With the above changes for the lighting I think I counted about 18-20 wires. What sort of plugs would you use & where can you get them?

Same for connection to my keyles ignition -- 5 wires but all 5 are very heavy -- seem like about 12GA so need a connector or two that'll work with that size/current capacity. I want to make it removable in case it has a problem -- maybe that's overkill?

Next, grounds. They seem to be one of the bigger causes of electrical problems so I'd put a ground bus up under the dash & ran ground wires for most things back to that bus. Good idea/bad idea?

If it's a good idea, does it make sense to use 3 12GA runs (one with wires through the firewal, one to the tail section, & one for the cabin) & splice off of that using the gauge of the power lead for each device? Or, should seperate ground wires be used for each circuit?

I pulled junction strips from mid 90's GM trucks I pick power and ground from the battery all my system grounds
run to the ground strip same as picking up power and I pulled double side plugs from vehiches from junkyard
for my dash I can unplug it and remove it complety all my splices and computer conections are soldered the rest are crimped

jim

Hey Rob,

Here's a picture of a dash I did for an old truck. The big connectors are weatherpac, the smaller one is a 9 pin computer connector and the battery in and ign out are spade connectors. The ground wire is an eye connector that goes to the chassis. The dash is removeable in minutes and includes 7 guages, ign switch, heater and wiper switches and sound system connections.

Pretty much any connector that will handle the load is fair game. Just make sure that you choose ones that you can't miss connect.

Cheers
Fred

Susan, let's start with what kind of car, year, etc.

Well obviously it's the Lucas electrics isn't it? ;-)
No, seriously Susan, one of the first things to do is check for good contact at the fuses. Often a little fine sandpaper will clear the trouble right up. If it isn't that it's probably corrosion someplace else.

JB