MG Car Repair: How do I correctly wire in a replacement solenoid?, inertia switch, fuse box

Question
QUESTION: Hi!
I have a just installed a new solenoid for my 78 B.  I have identified the correct terminals for the white brown and the white green(back to the coil).  I am having difficulty with the browns, and the wire straight off the battery.  I have 3 ilet connectors for the browns.  One is thicker gauge than the the other two.  Does it install on the top stud or bottom stud? The other two ilet connectors actually have two smaller gauge browns going into ilets.  According to Haynes, one ilet is for the alternator, and the other I think goes to the relay and fuse box.  Which studs do these go on?  and which stud gets the battery terminal cable??

Thanks

ANSWER: Hi Ted,
There are two large threaded posts and two flat spade terminals on the solenoid. One threaded lug gets the strap coming out of the starter motor. The other threaded lug gets the battery cable and all of the brown wires. The two flat spade terminals are each a little different size and the two flat spade wires are sized to match the two terminals so they can't get mixed up.
Howard

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

QUESTION: Hi Howard,

thanks for the advice, it worked.  HOWEVER, a major problem occured.  I had just wired in a brand new loom and completely fried the ignition circuit wire (solid white)when I was testting the connections.  All the lights, horns, interior lamp on the dash, harzards, flashers worked.  As soon as I turned the key and the ignition light came on....POOF!  Needless to say, $420 down the drain, and I was trying to be careful to avoid doing that.

The old loom had the exact same problem, as the white wire had been destroyed completely and a suspicious yellow wire had been wired in, to bridge the connection to the ignition, relay and fuse box.  The fuel inertia switch leads had been cut off.  I figured the person who did it had no clue what he was doing.

The car is a 78, but has twin SU carb set up, and an older style distributor Lucas 45D4 with ony one black wire to connect.  It doesn't have the amplifier.

The problem may be that the new loom does not have ballast resistors going to the coil, and too much current was going through.  If that was the case. I would have expected the coil to be very hot, but that was not the case.

Any ideas?

Thanks
Ted

ANSWER: Hi Ted,
Any time you replace any part of a harness or repair wiring, you should have the battery cable disconnected and test the cable to battery post with a test light and confirm NO LIGHT. Then install a in line fuse (35 amp) between the cable and the post and start operating all accessories and components. When you have turned on and off all electrical components (including ignition) and the fuse did not blow, then and only then should you connect the battery. In the dealerships I worked in, I had to use that procedure to be safe.

For tools you must have a wiring diagram, 12v test light and an inline fuse with 35 amp fuses.

If you don't have a diagram, you can download one from my web site.
http://mg-tri-jag.net/78-80MGB1x1.jpg
http://mg-tri-jag.net/78-80MGB21x1.jpg

Howard

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

QUESTION: Hi Howard,

It turns out that I got very lucky, and was able to save the harness.  It was not as bad as I first anticipated.  Taking your advice, I have checked all the circuits, and everything works as it should.

I have one small issue with the brake failure switch on the master cylinder.  I replaced the old switch because the master cylinder leaked slowly from it.  After putting the new one in, the same thing is still happening.   It's not leaking from the threads, but rather from the bottom terminals... I find this quite odd.  How does this switch work and is it time for a new master cylinder?

Thanks

Ted

Answer
Ted, the failure switch is activated when a difference in pressure between the two sections of the master cylinder forces a plunger (piston)toward the lower pressure side and thus operating the switch which in turn turns on the brake failure light. When fluid leaks out of the switch area the seals on the plunger are bad. The switch will not seal the fluid in.
Howard