1970/75 MGB GT - 13/02 Crossmember removed!

I'm sure the heat shield is asbestos so be careful I replaced mine with a stainless one as it was starting to disintegrate.

I still haven't managed to start the car. I've replaced the missing ignition wire and wired the plug into the wires (no socket left on the main loom) but have two wires left over. One in the plug, and one purple wire with a spade connector towards the ignition switch itself (brand new part from MGOC spares).

I've checked the earth on the battery which is fine and then the + all the way to the starter which has some new wire fitting installed. Bench testing the starter made it shoot forward but not spin, so I purchased another which was working when removed. This new one shoots further foward but does not spin - my dad suggests this is because we can't apply power (or enough power) to all the connections required.

With this 'new' starter installed, and the ignition wire installed, with a new battery fully charged, when turning the key I can hear and feel the starter relay click and the interior light dims slightly but nothing else. I have an ignition light on the dash, and the horn and washer/wipers work.

What's the next thing to check out? I have replaced all the fuses and fixed some dodgy looking wiring, cleaned the connections on the starter relay and solenoid and cleaned some earths.

I believe my car has an ignition relay between the fusebox and radiator (though I don't think this year should). Information on this relay is very sparse. I took it apart it looked fine, however the connections were very corroded and took some of the spades with them. I cleaned and replaced them but think I have damaged the relay in the process of reinstalling it, as now the starter relay does not click.


A few questions:

- What can I do next?
- Can I replace the starter and igntion relays with off the shelf versions (what amperage should I be using)?
- Can I bypass these relays to test the system out?
- How can I properly bench test the starter and solenoid (get it spinning)?
- Is there anywhere I can simply buy the socket from the main loom to plug the igntion socket wiring in?


Thanks, I'm terrible with electronics!

Unfortunately the Haynes manual isn't that helpful for these parts

OK, so here's a better explanation of what my issues are.

First off, the car is a '75 (P-reg), it has the earlier dash but the only wiring guide that seems to fit is the 'Late US Market MGB from Haynes'.

The car had previously had an attempted hotwiring, they smashed the steering wheel cowl, and ripped out the ignition wiring as seen below:



Off the main loom the plug/socket this igntion switch wiring this connects into has been removed, leaving me with loose pins:



I ordered a brand new replacement igntion switch and istalled it. I replaced the pins on the above with smaller ones that could fit in the socket of the new ignition switch wiring (above right). The fit isn't perfect but they stay inside and should carry the charge.

Now all these four wires are connected to the correct colour, but I'm left with a grey (slate) wire in the socket and a purple wire heading towards the ignition switch:



The grey leads to (I think) the anti run-on valve and switch which shouldn't affect starting, and the purple above leads to the key in igntion warning buzzer which is not fitted to my car.

Now, underneath the car:




The positive cable from the battery looks in good condition from the battery to the top of the solenoid (bottom bolt here as it hangs upside down) as are the multiple brown that connect to these. The white with brown and white with green look in good condition although previously spliced. I have replaced the connectors on one of these, as well as cleaned up the spade connector on the brown wire seen above.

This starter motor is a replacement part. The previous one when bench testing shot half way forward but did not spin. For this one, the seller was sure it worked and when bench testing this new starter it shot completely forward but did not spin but I think this is because I cannot put enough power through it.

Now with the igntion wire and new starter installed and connected as correctly as I think is possible, with a good charged battery, when I turn the key the igntion light comes on, and the horn and wipers and washers work.

When turning the key to the start position the starter relay clicks:



And the interior light dims slightly but nothing else.


My car is strange in that it also has an igntion relay left of the fusebox (unplugged for this picture) which only seems to be on later cars:



I don't think this influences the starting circuits however but it's strange that it's on.


With the fusebox I have a few questions:
- With the two pins on each side of the fuses, does it matter which one the spade is plugged into?
- Originally the two brown on the bottom left were combined (badly) into one as one of the spade connectors had snapped off. I moved this broken spade to the double white above which connects to a single - is this a problem?


Sorry about the long post but it's the only way to explain it all. Open to any suggestions, as previously said electronics isn't my thing!

Thanks Adam, it does help

I'm looking at page 32 (75/76 UK market cars), 31 is the US market one, and yeah it looks correct minus the ignition relay which must be aftermarket.

Am I correct in thinking that to get the starter turning I just need the ignition switch, battery, fuse and solenoid working? I'm trying to eliminate what I don't need to check.

I'm going to head to an electronics store to get replacements for both the relays, even just temporary, as replacement metal block ones like the starter relay here are £20! The guys in there are pretty knowledgable but would I need to ask for a certain amperage, or know the pin diagram of these new relays?

I have some standard Rover/Nissan/Vauxhall relays in the garage that might be useful.

Don't remember reading it , but, did you check the earth strap between engine and 'chassis' (apologies if i missed it) and the other earthing points ...

Is the battery still under the back seat ? If so the negative cable will be to some point on/near the battery box...if it's been relocated to the boot then follow the negative cable to were it joins the body and check the state of the wire and connection , if wire is green and powdery the replace, clean the contact point.

The engine to body earth starp will be a braided flat strap usually between the bell housing and nearest body point ( you may have to go underneath to see/find it ...

There are various earthing points around engine bay for things like lights, horn etc the wiring diagram will help you identify and find them, just make sure all are secure and free from corrosion.

Yes it is, the earth looks pretty sound even if the cable is a little old. The battery is transferring power so I think that can be ruled out. I've found the engine to chassis strap in the engine bay that connects to coil bracket, which seems fine too. I cleaned another earth below the starter relay but couldn't find anymore.

I managed to get the original starter working on the bench correctly. Originally we connected the positive to the top terminal and another to the white & brown connection point, the gear would shoot forward but not spin. However with a fresh battery and connecting to the lower terminal directly the starter shoots forward and spins.

I'm assuming that the white & brown on the solenoid is not recieving power and joining the two terminals of the solenoid together spinning it up. As the starter relay clicks, and other electrical components work I'm also assuming that the earths are fine as the starter seems to have no earth of its own.

Thanks for the advice guys, I will test out the white & brown from the starter relay to see if current is getting through tomorrow - I think that's the problem of all of this. If not, it's either a secret earth I can't find yet, or an issue internally with the solenoid not connecting across its terminals.

I ran a replacement wire for the white/brown starter relay to solenoid wire but no change. I'll try it again but want to check the earths too. I'm having trouble finding them though. An excerpt from 'MGB & MGBGT Common Problems and How to Fix Them' suggests there's either an earth from gearbox to chassis rails, or one around the engine mounts as Adam suggested. It says that they made corrode to the point of disappearing.

Can anyone confirm these earths and take a picture? Facing the car, on the right of the engine I can see this on the engine mount:




Thanks