Electrical Wiring on Ignition

[Silascrum]

In trying to solve the electrical problems with my 78 fj40 I ran across a very interesting unexplained puzzle, atleast to me.

What is was doing: Smoking behind the dash whenever the ignition switch was on.

What I did: tore down the dash and started searching for the rogue wire(s)

What I found: An ignition resistor wire was ran from the ignition to under the hood, right past the hole from the dashboard to hood on the passenger's side. This bypassed the fusebox. Clearly done after it left the factory. This type of wire, which i've researched, has to be replaced every so often. They go bad. It had done its job and turned the electrical energy into heat energy, unfortunately melting other wires around it.

I just ordered my FSM today and am hoping these will tell me more. In the mean time I figured I'd hop on here and see what I could find out.

My question: Why was this wire placed in this position, bypassing the fusebox? What was the purpose of someone putting a resistor wire in there? Do I place another resistor wire in its place, or shoot for the way it came from the factory? So you can get a better idea here is the electrical diagram

http://www.yankeetoys.org/documents/wiring_diagram_78_fj40.pdf

the resistor wire was placed along the BY wire after the section that breaks off towards the ignitor and ignition coil. The one headed towards the fusebox, but there is another BY wire that was also there. This one still runs to the fusebox. After thinking about this again, I think i need to look at it further to determine where these two BY wires are actually going in my cruiser. Still lost...

If anyone has any answers to my questions above that would be great. Or just advice. Anything is much appreciated.

 

[bsmith123]

resistor wire

I couldn't open the schematic but on your points ign sys you should have two wires that power the coil. One is when the key is in the start pos this allows a full 12 volts to the points while cranking. The other should run through a ballast resistor to the plus side of the coil.

Assuming you still have the points system or original wiring and ign sys? Sorry I don't know if the 78s still had points. if not the principal might still be the same to reduce volts while running with the key in the "run" position


The resistor wire may have been a replacement for the ballast resistor if it went bad

 

[Pin_Head]

What is (was?) the color code of the wire? The stock coil wire is not fused and runs directly from the key switch to the coil. It is black with a yellow stripe. Apparently toyota thought it was more reliable and important for this wire not to be fused.

 

[bsmith123]

BY

looks like BY in the text ---should be black and yellow then I think

what kind of ignition did the 78s have did they run a ballast resistor--from what you said it must be between the coil and the points then--if it is points I don't know the FJ well enough to say, my 71 is my first

 

[FJ40Jim]

Do I place another resistor wire in its place, or shoot for the way it came from the factory?

The way it came from the factory is with coil power coming unfused from the switch, through a resistor wire to the coil. Power for the ignitor is also unfused direct from ignition switch.

Dunno if the resistor wire you're looking at is the stock one. The stock resistor wire is bright colored and labeled w/ "yazaki resistor" or something to that effect (yazaki manufactures harnesses for Toyota).

 

[Pin_Head]

I don't know what a "resistor wire" is, but '78s have ballast resistors in N America. The wire from the key goes to the end of the ballast resistor away from the coil + lug. There is another BY "ballast bypass" ignition wire that runs from the starter solenoid to the coil + lug. It provides full battery voltage only during engine cranking.

 

[bsmith123]

resistor wire

regular wire has very little resistance to current flow. Very low ohms with a meter, resistor wire has a higher resistance and limits current basically the same way as a ballast resistor---it just adds resistance to the circuit

 

[Pin_Head]

regular wire has very little resistance to current flow. Very low ohms with a meter, resistor wire has a higher resistance and limits current basically the same way as a ballast resistor---it just adds resistance to the circuit

Yes, that is one definition. AFAIK, there is no wire of this type normally on cruisers.

Another definition is a wire that goes to a resistor and there is a ballast resistor that has several wires going to it.

It is the ambiguity that I am struggling with.

 

[FJ40Jim]

In 1978-1980, USA cruisers got full electronic ignition. The ballast resistor used on75-77 ignitors disappears and is replaced by a resistor wire in the harness.

Note that on the 78-80 ignitions, there are 2 power wires, one into the ignitor and one to the coil. Measure the V and it will be 12V on the ignitor wire and about 6V on the coil wire.
They fixed that apparently on 81-later w/ a better ignitor that could switch a coil running at full 12V, so on those applications there is a single power terminal at the ignitor supplying +12V to coil & ignitor simultaneously. And the cranking bypass circuit finally goes away.

Googling turns up this generic explanation:
"The only time the resistor is out of the circuit is during startup, when the engine needs all the spark it can get. It's bypassed in the ignition switch's start position so that, during starting, the coil gets full battery voltage. Ignition resistors can take many forms, depending upon the manufacturer of the vehicle. Some builders mounted a big resistor on the firewall and some others utilized a special type of wire (resistance wire) running from the ignition switch to the coil. Still others used coils that were built with an internal resistor."

HTH

 

[Silascrum]

Yes, it does say yazaki. I thought for sure it was after factory because the connection that existed with that wire looked to be put in after the factory. It very well could have been something they found later that needed to be redone.

Either way, fact is I have to put another resistor wire in there. I would like to replace the parts of the ignition, the ignitor and whatever else, in order to do away with the resistor wire. How easy would this be? What else would I have to change? If not, this problem will happen again, right?

but for now...a few questions:

Can a replacement wire be found at my local parts store, or do I have to make a special order?

Is there anybody else that has had to replace this resistor wire?

It will be nice to drive her again!

 

[Pin_Head]

Either way, fact is I have to put another resistor wire in there. I would like to replace the parts of the ignition, the ignitor and whatever else, in order to do away with the resistor wire. How easy would this be? What else would I have to change? If not, this problem will happen again, right?

!

Sure you can get rid of the resistor. You have to get a new coil that is designed to run at 12V instead of 6V. That's all there is to it.

If you get rid of it, then you will lose the reliable start during cranking feature. The battery voltage drops to about 8V or less during cranking and this is marginal for making a spark with a 12V coil. Toyota eliminated this feature in 1981, but kept it in Canada.

The resistor is not the cause of the wire burning. Shorting out the wire causes it to burn, because it is not fused. Shorts will burn out the wire, resistor or not.

 

[FJ40Jim]

Either way, fact is I have to put another resistor wire in there.

Or install a conventional ballast resistor somewhere in the power path to the coil.

I would like to replace the parts of the ignition, the ignitor and whatever else, in order to do away with the resistor wire. How easy would this be? What else would I have to change? If not, this problem will happen again, right?

No problem. Install a coil/ignitor from a 81-87 Cruiser. It runs off a single 12V ignition source.

Dunno if the problem will recur. The Yazaki resistor wire seems to be bombproof. Never had a problem w/ one in a Toyota. Only replaced it in Fords & chevy.

Can a replacement wire be found at my local parts store, or do I have to make a special order?

The few times I've dealt with them, the new stuff came from the dealer, 'cause I wasn't sure that an aftermarket part would have the correct ohm/ft. rating.

Is there anybody else that has had to replace this resistor wire?

Only in 'murrikan cars.

Like Pin said, check carefully, make sure there is not a problem drawing too much juice through the wire.

 

[Silascrum]

I believe I found the short that may have caused this wire to go bad. I'll do a thorough inspection of the other wires in the dashboard and hope for the best. It could honestly be anywhere. There are so many deadend wires. It may have originally been caused by the fix I had done to it a couple months ago. I don't have a way to check the amount of voltage right now.

I'm gonna go get another resistor wire, fix the shorts, and put it back to the way it was from the factory. Then cross my fingers.

Thank you all for you help!

 

[Pin_Head]

You will be fine staying with the stock wire. You have to get up pretty early to out think the Toyota engineers.

 

[Silascrum]

Well there is a problem in getting this wire replaced. I've called the two closest toyota dealerships in my area and both can't help me out in finding this wire. I also went by a carquest and they were suggesting I replace it with a fusible link wire. (I didn't think that would work, or will it?) I guess because so few have needed to be replaced they just don't have them. I'm gonna go by one of the dealership tomorrow and see what they have.

Not sure where to go if they don't. There is the small possibility that I can repair this wire, although there are some spots that are really bad and due to the fact that this wire is supposed to get hot, I don't think this is the best idea.

Does this wire have to be a certain length? If not then I can remove the bad portions and make the overall wire shorter. what do you all think?

 

[bsmith123]

Resistor Wire

If the insulation is cut and the rest of the wire is ok then just repair the insulation with something that will hold up to the heat generated

You can replace the resistor wire with a plain wire if you use another resistor in it's place such as a ballast resistor just make sure it is the correct ohm and amp rating. If you replaced what you have with a matching coil and resistor from another vehicle it would work okay I bet.

Another option is to use a coil with the resistor built in and run plain wire.

You can check at the auto parts and probably work it out


changing the length of the wire will change the resistance but if it's only a little then it will probably be okay. you could check the change before and after with a ohmeter


If you do find new resistor wire buy double length and run a spare with terminals alongside the new wire and mark it spare in case you ever need another


sounds like your on the right track finding the short

 

[Silascrum]

Can I use a fusible link wire in the place of this resistor wire? From what I'm reading about fusible link wires, I can but, have to get the correct guage.

 

[Pin_Head]

Like Jim C said, just get a regular ballast resister used on earlier cruisers and run a copper wire (about 12 ga?) from the key to the resistor. Cheap, easy, effective. Napa will have a generic ballast resistor.

 

[FJ40Jim]

Can I use a fusible link wire in the place of this resistor wire? From what I'm reading about fusible link wires, I can but, have to get the correct guage.

No, fuse link is still a wire, no specific resistance rating.

 

[Pin_Head]

Can I use a fusible link wire in the place of this resistor wire? .

Just to reiterate: If Toyota thought it would be a good idea to fuse this wire, they would have put one in.

Just make sure that the wire is well insulated and not rubbing against any ground.