MG Car Repair/1970 MGB


QUESTION: Limited mechanical ability but trying to trouble shoot my 1970 MGB. Car would not start, replaced battery, still not start, not even a click. Starter motor? Alternator? Recently new fuel pump. Any suggestions as what to do next?


ANSWER: Hi Michael.  I really need to know if you have any other electrical troubles.  Do the headlamps work OK?  Does the horn work?  With the ignition switched on, do the accessories such as the heater blower still work OK?    

If everything is OK except the starter doesn't work, then I would diagnose a failed starter relay.  You can check it yourself, but on a USA car you will need a helper.

Open the hood and locate the fuse box, which should be attached to the inside of the passenger side front wing (fender).  The starter relay is an oblong tin can between the fuse box and the fire wall.  It has about 4 wires going into it, one brown, two white with coloured stripes, and one black.  It is shown as part #54 in this diagram:  

Put your hand on the metal can and get a friend to turn the ignition key to operate the starter.  

o If you cannot feel the relay click in and out then the relay has failed.

o If the relay clicks in and out but the starter does not operate, then the starter has failed.

Give this a try and then get back to me for more advice.  

---------- FOLLOW-UP ----------

QUESTION: Horn and lights do not work. Nothing happens with starter relay when ignition is engaged. Is next step replace the relay?  Living in Montana I assume either order through Moss Motors or find a closer source?
Thanks for your input.  I was worried I was going to have to haul the car 70 miles to nearest garage.  Hopefully I can fix myself.
Again, appreciate your assistance.


ANSWER: Sorry, Mike, but you have a bigger problem.  If the horn and lights do not work then it is nothing to do with the starter solenoid.  You have a total power loss.  This is usually caused by a bad connection in the main wiring, often a battery connection problem.  

The good news is you may not need to buy anything.  All you need is a voltmeter with a 20 volt setting or similar.

Start by visually checking the earth wire to the driver's side battery.    

Then check the voltage through the link wire between the batteries (6.5 volts or so) and then test the power terminal on the passenger's side battery (13 volts or more).  You are looking for a lack of voltage somewhere.  There should also be at least 13 volts at the BIG terminal on the alternator and at terminal 1 of the fuse box.  

Let me know how you get on.

---------- FOLLOW-UP ----------

QUESTION: By "earth wire" I suspect you mean ground wire?  BTW when the car came to the US it was converted to negative earth. Does this matter?


Sorry, Michael, I forgot that we talk of earth wires here in the UK, not ground wires.  

I don't think your car needed to be converted.  The design of the MGB was changed from positive ground to negative ground in 1967.  The changeover was in the Fall of 1967 at chassis number 158230.  

MG Car Repair

All Answers

Answers by Expert:

Ask Experts


Barrie Jones


MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.


I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

MG Car Club.

Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

M Phil, C Eng, BSc (Eng).

©2017 All rights reserved.