MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - alt wiring & shock fluid

First let me thank everyone for all your help so far.
Now that the engine is running in my 72 B I am not getting any charge from the alternator.
I have checked the brushes and the internals of the alternator everything looks fine.I dont have the wiring to the shift console conected but I didnt think this has anything to do with the charging system. But on my alternator the 3 pin L shaped connector has one brown wire and 3 brown yellow wires. This doesnt correspond to any of my wiring diags. what are the 3 br/yel wires for and where do they go?? could they have an effect on the charging.. The alt warning light is working and goes down to a dull glow when the engine is running, Any thoughts would be appreciated.
Second issue, what is the large bolt for in the bottom of the rear shock can it be used to drain the shock for flushing and also what fluid is best for the rear shocks ? Thanks again Brian
B R pasmore

Brian, I believe there should be only one brown and yellow wire. It goes to the ignition warning light. Are all three wires tied together? The alternator spade closest to the engine, on my car, has a single brown and yellow wire going to the ignition warning light. I guess you need to locate the wire going to the light and then determine where the others go.

During a recent telephone conversation with the president of World Wide Auto Parts I asked what type of shock fluid they used. His answer; 20w hydraulic jack fluid. He went on to say you could use 20w motor oil but foaming may be a problem, otherwise it would work fine and not harm any internal rubber parts. The book specifies mineral oil. The large nut on the shock is the valve and it can be removed to help drain the fluid. Just be careful not to lose the spring or any shims and other part that are under the nut. To change the fluid it's best to disconnect the damper arm so you can pump out the old fluid and expell any air when refilling. Good luck, Clifton
Clifton Gordon

BR:

For your alternator, I would suggest that you check out your wiring to see where each wire goes. You should have a white wire entering the dash warning lamp at one of its terminals or leads, and then a brown/yellow lead leaving that lamp out the other side. What I have seen happen, on occasion, is that sometimes the other end of that white wire will be misplaced such that it draws current from AHEAD of the ignition switch rather than after it like it is supposed to. This may not be your problem, but it is worth making sure that it is not.

If you take a look at the wiring diagram for your year, you should see that there are only these two wires - Brown and Brown/Yellow connected to your alternator and that the single Brown/Yellow is wired as described. I would check each of these small wires by running a continuity test from each wire end back to the Brown/Yellow wire connection at the dash warning lamp. Use only (the) one which has true continuity to that lamp, and then bend back and tape up the others.

If you want a better discussion of alternators and their wiring, you might want to take a look at these sites:
http://www.mgb.bc.ca/electrical
http://www.vtr.org/maintain/alternator-overview.html
http://www.mgb-stuff.org.uk/
http://www.mgb.bc.ca/service/lucas-colours.html

Bob Muenchausen

The fact that the warning light glows indicates (ho ho) that it is connected to the alternator, and this is required as a 'pump primer' to start the alt charging by 1000 rpm or so. The fact that it dims when the engine is running could indicate that the alternator is giving some charge but not a full charge due, for example, to faulty diodes in the alt. On the other hand it could be due to bad connections somewhere in the cars wiring. The warning light acts as a pair or balance scales between the system voltage on one side and internally to the alt on the other. Normally when the engine is running these are at the same (or very nearly) potential so thare is insufficient potential difference to light the lamp, i.e. it has 14.5v (or thereabouts) both sides. For it to glow one side must be higher or lower than the other. If the brown/yellow is at 14.5v and the white is noticeably less then the alt is charging correctly but there are bad connections in the brown - solenoid - brown - ignition switch - white circuit. Measure the voltage with respect to ground on each side of the warning light, the white side usually connects to the rest of the white circuit near the ignition switch.
Paul Hunt

This thread was discussed between 05/05/2003 and 07/05/2003

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.