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MG TD TF 1500 - Electric Starter Switch

I'm considering replacing my mechanical starter switch with an electric circuit. I'm assuming that I can simply install a heavy duty relay and activate it with a dashboard switch. Is this feasible, and if so, what size relay should I use?
Corey Pedersen

You are talking about a "Starter Solenoid" The issue is whether you have a positive or negative ground.
You will need to watch out for this. Some but not all have two solenoid winding terminals along wit the two starter cable terminals.
Here is one from the NAPA catalog.

These will work with either polarity.
JA Benjamin

Don't know why you couldn't use a starter solenoid from an early -positive ground- MGB. Moss sells a reproduction (546-152) for $19.30.
David Werblow

Don't think I've ever seen a polarized starter relay. I just put one from a Ford Taurus into 'the53' so that I could have a remote starter switch. Bud
Bud Krueger

Bud, there is a difference in construction- not sure about polarity. We had an old Ford diesel tractor and I think the small terminal completed the ground to energize the coil and crank it, rather than to apply hot. I remember because I got the wrong one. My question: yes it can be done, but why? You are adding an extra switch and wiring, nothing more simple and reliable than the stock setup. George
George Butz

I started on this concept because I bench-tested my existing switch and it seemed a bit "tired". George, on reflection, I think the best solution is simply to replace with new.
Corey Pedersen

A switch should not be polarity sensitive, not sure what the issue is?
D. Sander

The polarity usually doesn't matter. Here's a link to Cole-Hersee. download the solenoid catalog. I've used many of their solenoid switches both in cars and trucks and the pvc coated models in boats.

The catalog not only shows the internal wiring but shows the relationship of the terminals so that if you want to use a one wire (where the battery terminal supplies one end of the pull-in coil and your start button supplies the ground)so that you can have the same relationship of battery cable and starter cable. Wordy sentence, I know, but look at the 24060 and 24046 models for comparison.

I've used their PVC coated types on a boat winch where they're subject to salt water spray and they were 100% reliable. I also use their relays anywhere there is a heavy load I don't want to put through a switch. My plow truck has all sorts of backup lights and an alarm. There's no way the backup switch would take it so one of their continuous duty solenoids takes care of it.

J E Carroll

It's not uncommon to have four terminals on a starter relay. One large terminal is for input power and one large one for power to the starter. One smaller terminal is for the actuating switch, often requiring a simple closure to ground. A fourth, small terminal, is often a closure to the input power terminal and acts to bypass a ballast resistor while the starter is cranking. I believe the MGB relays are of this type (as is the Ford Taurus one that I used).
It's not difficult to push in the starter switch extension from under the bonnet as long as you have a pull cable that's stranded. It's a !##&$ to try to push it in if you have a solid inner cable. It's much easier to just thumb a pushbutton. Actually, I put the pushbutton on the fascia where the starter cable should be. It's black and is very unobtrusive. I may leave it there and glue a knob on the end of the to emulate a standard pull knob. Bud
Bud Krueger

I had endless troubles with the mechanical starter switches on my two 1600 MGA's (coupe and roadster-eg. burning the copper contacts). I finished up using the original knob/switch to turn on a solenoid which is hidden under the large heater trunking and I have used the blanking plate bolts to mount the solenoid. I note that MGB's had a solenoid so the factory must have thought that the mechanical switches were a problem! The original switch now has to only cope with a few amps instead of the full force of the battery!
Barry Bahnisch

Sorry, I thought that I was on the MGA site! Some of my comments may still apply.
Barry Bahnisch

A lot of solenoids look alike, but wire differently. Some have 3 terminals and others 4. Some are internally grounded and others aren't. Helps to use a meter or battery charger to sort out the wiring. Seen a variety in the hydraulics business.

It takes a pretty healthy button on the dash, capable of handling a few amps.

I put a slick one on wife's TD, an old 6V Ford solenoid. Yes, it draws a touch more than 12V solenoid, but it has a button on it to push to engage. I often pop the bonnet, turn the key on, tickle the SU, push the button and wave the butterfly. Helps to have it in neutral!


...mine uses an MGB solenoid with an old Austin starter switch...never changed it back and never have had a problem...
gblawson(gordon- TD27667)

This thread was discussed between 20/10/2012 and 24/10/2012

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