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MG TD TF 1500 - 1951 TD/c-8151 firewall grounds

I swear my brain is in a fog since my accident.

I’m trying to get my wiring finished. Hooked up the battery and no circuits energizing. Cleaned the contacts on the remote cuss block and installed new 35 and 50 amp fuses. Still no joy. No starter, no pumps , no lights. When I wired the car in had continuity at the pigtails for the lights. The starter worked and the pumps and ignition were hot wired at the time and worked as well. Main engine/chassis ground, battery to firewall ground and rear chassis to harness ground at intact. But I have two ground wires that exit the main wiring harness on either side of the firewall to connect yet. Where are these supposed to be attached? The eyelet hole size appears to be 1/4”. Do they attach to the horn to mounting bracket bolts? Or?

Bill Chasser
TD/c-8151





W A Chasser

Is the battery earth cable making good contact with the painted tub Bill at the side of the battery box? Have you fitted the earthing strap from the bell housing on the engine to the chassis? Sounds like earthing (ground) issues to me. I've often wondered whether one of the so called unused holes shown on the drawing in Malcolm Green's book might be for the earth? The other may have been for a clip to secure the fuel line? Cheers
Peter TD 5801
P Hehir

Bill,

In the first picture, there doesn't appear to be a connection to the fuel pump.

David

David Padgett

Bill,

Sorry, my previous comment should read, 'In the first picture, there doesn't appear to be a power connection to the fuel pump.'

Also, the pump should have a ground connection fitted under one of the pump body screws. You cannot rely on the pump support bracket bolts to provide a good grounding point.

Perhaps that is the purpose of the floating cable with the eyelet shown in picture 1.

David
David Padgett

Peter yes as I stated in the OP. The battery to battery box ground, engine to chassis ground, and the rear ground wire to the damper grounding bolt are intact

David. Good eye. You are correct I do not have a hot wire connecting the second fuel pump. And although you can’t see it, I do have a ground wire on both fuel pumps. (Black wire looping the bottom of the pump housing).

I’ll continue searching out my power fault today.

I still need to know the correct location for these two ground wires.
W A Chasser

Bill: I think the left ground goes to a hole on the firewall next to the coil.

The right one one to a hole on the firewall just above the horn bracket.

But on some cars I see these as unfilled so ...

I have seen some cars with this ground on the flexible horn bracket upper bolt. See the gallery.
Christopher Couper

Chris is probably correct even though Green lists these holes as unused. It is something of am mystery Bill. I didn't understand your term "Cleaned the contacts on the remote cuss block" which is why I asked about the earthing points. A poor earth or dirty/poor/oxidised or loose electrical connections are almost always the cause of the symptoms you describe. Cheers
Peter TD 5801
P Hehir

Sorry spellcheck error. Should have been fuse block. I try to catch spellcheck as it often changes my word spelling even when they are correct. I missed that one.

With the help of extra hands from my neighbor we’ve sourced a potential power issue. It seems my NOS early style key switch isn’t putting power onto the IG post white wires that feed the pumps, coil, fuse block, brake lights, and fuel sender. But the reality is it is not feeding anything. next step is to crawl under the dash of TD-4834 and photograph the wiring to the switch and compare it to TD/c-8151. If I made no errors I’ll have to pull the switch apart for inspection/ lubrication or put a used switch in its place for the moment.
Another one step forward and two steps back.

Bill Chasser
TD/c-8151
W A Chasser

If you need help with the ignition switch Bill email me. I can understand how a NOS switch could be defective as I've pulled apart about 70 NOS military switches that I purchased for parts. These PLC 6's had no lock, just an ON/OFF knob. Those few that weren't still in their original stapled and unopened boxes and wrapped and taped in their waxed brown paper were more often than not rusted inside. I also firmly believe the ignition switches sold today are rubbish. Those that do work have proven to have a very limited life. For the fastidious restorer the correct switches for the TC and TDs up to sometime in mid/late 1951 had the MRN series lock. The remaining TDs all used the FA series. These original switches were made without the window. Those with the window were later, albeit original LUCAS 1950's replacements, but their locks were the FS and FP series. The original keys were made by Wilmot Breeden Union. There is a typo in the article that I'd written on these switches some years ago. The thread is actually 5 BA not 4 BA as I'd stated. The nut IS 6 BA across the flats however, but is taller than a 6 BA available today. Removal of the soldered nut can be a slow and frustrating process as care needs to be taken to ensure that the nut isn't damaged. I've not found a source anywhere for these weird original hybrid brass nuts. Cheers
Peter TD 5801
P Hehir

Peter check your email.

I had sent you an email before your last reply. This is a correct NON window PL6 with a MRN tumbler. I forgot how to get the thing apart. Can you email your write up. I know I have it somewhere but can’t come up with it. My mind is not the clearest at this time. Dad and I restored the one in my other car but that was 6-7 years ago. And I don’t remember how to separate the pieces and don’t want to damage them. I was going to try another used switch I have but it is a FS tumbler without a key

W A Chasser

Bill,

Had a look today re the grounding wires query.

I replaced the loom on my car when I did a complete restoration twenty years ago. I recall making notes, unfortunately no photos, about anything relating to wiring that wasn't clearly obvious, connection location-wise, from the circuit diagrams in the WSM.

Also, from the very poor state of the old loom, I would guess that it was quite probably an original factory-fitted loom. Accordingly, I copied the original arrangements when fitting the new loom.

The left ground eyelet is attached to the left attachment bolt of the coil mounting bracket.
The right ground eyelet is attached a bolt on the right horn mounting bracket (but not one of the bolts holding the bracket to the firewall).

Hope this helps

David

David Padgett

Sure Bill. I'm about to send you Revision 4 October 2020. This corrects some earlier typos from 2015 and will be published in the TTORC magazine sometime next year. Cheers
Peter TD 5801
P Hehir

"These PLC 6's had no lock, just an ON/OFF knob." That should have read PLC 2's, not PLC 6's. Cheers
Peter TD 5801
P Hehir

David. Perfect !! That makes sense now. Thank you.

Peter I just sent you a second email. In reading it I couldn’t make sense out of it. That you for your response here. I am watching my Email box

Bill Chasser
TD/c-8151
W A Chasser

That auto correct has a mind of it's own Bill. Glad I don't have it on my PC. Also happy that you got your copy of Revision 4 from your junk folder. I've changed email addresses which was creating the problem at your end. Studying the pics in Chris Couper's gallery should also shed some light. I find his resource invaluable. Cheers
Peter TD 5801
P Hehir

This thread was discussed between 17/10/2020 and 19/10/2020

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