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MG MGB Technical - 1977 MGBGT Starter Wiring

I am wiring my '77 V8 Conversion and have a problem with the starter/coil area.
I have fitted one of the new geared starter motors which only have two terminals - one on the starter for all the brown wires and one only on the solenoid. I am using the original loom which I assume has a built in resistor. My problem is that I have a white/green and white/brown coming out of the loom adjacent to the starter but only one terminal. Would appreciate advice as to correct connection procedure.
Many thanks
Peter M
Peter Malkin

Peter -
You need the hook the NW to the solenoid connection To activate the solenoid. The W/LG feeds the coil with straight 12V when the starter is active. Trouble is, you don't want the 6 or 7V from the ballast resistor to backfeed the starter or the solenoid, which is why the correct starter solenoid would have the second terminal to feed W/LG. This terminal is isolated from everything else when the starter is not active, and connected to 12V when it is.
So, you can try to get the correct solenoid, or you can connect the WLG to the single solenoid terminal (with the NW) with a diode in-line on the WLG to prevent backfeed. I don't know much about spec'ing the diode, somebody should come along soon! Alternatively, you can arrange a relay operated by the NW, which turns on power to the WLG when the starter is active.

FRM
FR Millmore

Hi Peter, FRM

I would suggest that a relay would be the better option, as a diode would need to be capable of carrying a minimum of 4 amps, possibly 8 amps with a 6V coil, not unobtainable but would need heat sinking and be robust physically to cope with a car environment, which would be a pretty hefty device. A relay, on the other hand is small, intrinsically robust, readily available for a few dollars and is almost fool proof.

Herb
H J Adler

Although in theory a diode would work I also would prefer to use a relay for its robustness - a diode going open circuit wouldn't really be noticeable, but short-circuit it would quite likely keep the solenoid operated and the starter churning.

As well as one side of the winding going to the brown/white of the starter relay (or white/red for that matter) and the other to earth, I'd take one side of the contact from white at the fusebox, the other going down to the dangling wire at the solenoid, or direct to the coil with the dangling wire taped up.
P Hunt

Thank you FRM, Herb and Paul - have opted for the relay.
Kind regards
Peter M
Peter Malkin

Good. Don't really know why I suggested a diode - has to do with thinking of the function, then I always opt for a non electronic way to do it = relay, since I dislike solid state stuff - can't trust 'em!

FRM
FR Millmore

"I dislike solid state stuff - can't trust 'em!"

Ditto electronic ignition, pointless fuel pumps ...
P Hunt

"solid state" = condition of being inert; frozen; lifeless or dormant; motionless.
FR Millmore

Gentleman, this is the 21st. century after all. Everything is now electronic whether we like it or not. RAY
rjm RAY

"Everything is now electronic whether we like it or not"

Everything *new* might be, we have the choice of how
much we put into our MGBs. Thank goodness.

"Progress isn't necessarily the same thing as improvement" - EIIR
P Hunt

Alternatively keep things really simple, get a 12V coil and bypass the resistor wire completely.
Chris at Octarine Services

For that matter just leave it disconnected and keep the 6v coil, that will give exactly the same results as changing to a 12v coil and bypassing the harness ballast, but cheaper and less work :o)
P Hunt

C'mon guys, poor Peter is in Australia, and I'm sure he needs every bit of fat spark he can get to start his car on a cold winter morning, after he shovels the two feet of snow out of his driveway!

FRM
FR Millmore

FRM, solid state stuff is perfectly reliable as long as you don't let the magic smoke escape!

I am busy wiring up the entire car now. What a mission! Am using an Advance Autowire loom which does include relays for everything and much, much thicker wires than standard.

I have the opposite problem. My starter has two small terminals and I can't remember which is the relay connection and which is the 12 volt feed to the coil! I have a 12 volt sports coil and no ballast so I don't need that I think.

I am guessing if I attach to the wrong one it just won't do anything.

Simon Jansen

Hey FRM
I live in a part of Australia where we have snow all winter and 40deg+ in summer. I don't use my MGs in winter as I'm too busy sliding down hills.
Thanks for all comments.
Peter M
Peter Malkin

Simon -
"perfectly reliable as long as you don't let the magic smoke escape!"
One of the devious tricks of solid state things is that they sometimes have no majic smoke outlets at all. Ask my daughter. Her 5 month old $1500 MacBook Pro simply stopped working, as she was using it in her dorm two weeks ago. She foolishly told the Apple people that a couple of drops of condensate from a water bottle had dripped on it. They contend that the thing is "water damaged" and that neither the standard nor the not cheap extended warranty cover it, and want $700 to fix it. It certainly has never been wet, and anybody who would make a device intended for routine use by students and the like that won't take getting a couple of drops of water on it is a scoundrel. So, I will soon get introduced to advanced computer electronics; fortunately I will have on hand a couple of real computer engineers.

"My starter has two small terminals " Checked by meter to earth, one terminal will have open circuit or infinite resistance - that's the ballast bypass. The coil will have a couple of ohms = the start wire from the relay (NW)or switch (WR)
You are also correct that hooking the start wire to the wrong one will result in nothing.

FRM
FR Millmore

FRM, I think these days Apple just expect people to buy what ever the shiny new Apple product is no questions asked. Why do you need a warranty when you can buy the latest thing brand new!

Haven't been a big fan of Apple since the Apple 2 days when you used to get a circuit diagram in the back of the manual!

Another day of wiring ahead of me.
Simon Jansen

Simon,

The two spade terminals are different sizes - the smaller one is the ballast bypass circuit.
Chris at Octarine Services

I rewired my car a few months ago & completely forgot about the relay for the 12V cranking issue. It wasn't until this subject was posted that it jogged my memory. The car starts first time every time. I realise we're in summertime now & it might be different in the wintertime. Another thought is , maybe the smaller starter motor doesn't sap the battery voltage so much as the original does. I still intend to fit the relay though. Barrie E
B Egerton

"The two spade terminals are different sizes - the smaller one is the ballast bypass circuit."

I think that was the case originally, Chris, but I have seen rebuilt units with the same size spades.

*Geared* starters are supposed to take less current for much the same cranking speed and so any given battery voltage should drop less with them. I didn't have one on my V8 long enough to measure it though, but would be interested to hear of some examples.

A 6v coil with ballast and no bypass will perform pretty-much identically to a 12v coil without ballast, and so under most conditions will start just as well. Bypassing the ballast really only comes into play under adverse conditions e.g. weak battery, very cold weather, poor state of tune etc.
P Hunt

Chris -
As Paul says, I thought they were different sizes, until I started meeting same size ones, and then one with one each male and female terminal.

Barrie E - also in agreement with PH, you just wait - you will regret not having that 12V bypass on a cold winter day with 2 feet of snow on the ground!

FRM
FR Millmore

The relay has now been fitted. The thought of shovelling 2 foot of snow next winter really spurred me on
P H ,Re the starter motor. Where would you like me to take voltage readings from ? Any specific points?
Barrie e
B Egerton

Barrie - The battery posts ideally, to eliminate the voltage drops in the connections and cables from there to the starter. But if you reckon those are 'good' then between the brown at the fusebox and a body earth nearby will be almost as good and probably easier.
P Hunt

This thread was discussed between 16/12/2009 and 22/12/2009

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