Ignition light issue

[Stevemorris]

OK, Now I am beginning to 'get to know' my car...

Misfire cured, turning my attention now towards electrics.

Initially, there are a few issues regarding the usual poor connections from being stood a while, which I am working my way through methodically. Electrics never phased (see what I did there,,) me. I worked as a technical trainer for years after 30 odd years on the tools.

One thing that's puzzling me a bit, the ignition light. The light comes on when I switch the ignition on but only for about half a second, then goes off. Car then starts and ammeter is showing charging, plus ive tested the voltage at the battery, around 14 V when revs picked up, so it's charging.

Before I go ripping into it has anyone got any thoughts or ideas?

Thanks,

Steve.

[mgcjag]

Hi Steve...do you have a wireing diagram for your model...see knowledge base.....early cars have oil pressure switch connected to red light in speedo (ignition warning lamp).. goes off when pressure builds on start....or do you gave the 3aw ignition light unit....Steve

[mgcjag]

This may help viewtopic.php?t=18689

[Stevemorris]

Hi Steve, I dont think it's the oil light as the light goes out almost instantly when I switch ignition on, not even cranked it. Ill take a look, been doing a search on here and its under the heater box (3AW) if I have one? Yes I have downloaded the wiring diagram, thanks for the steer, the diagram I think mentions something about ignition pressure, maybe it means either or? Thanks, Steve.

[mgcjag]

Hi Steve....the ignition pressure switch is just an oil pressure switch that operated the ignition warning lamp on the dash...as per info in the link I posted...Steve

[Stevemorris]

Hi Steve, Yes thanks I got that.

Interesting one this, according to what I know, the earlier cars with the oil switch were in use until 1967 which is when the 3AW control unit was fitted? My car is a 65 model and there is no 3AW module fitted, which would I guess be correct. Trouble is, there's no oil light switch screwed into the block either, BUT... I know my car has had a 7F (420) block fitted which is dated 1966, so maybe the switch wasn't on the 420 donor and just hasn't ever been fitted???

More investigation required methinks!

Regards, Steve.

[mgcjag]

Hi Steve....have a look close to the dizzy...for the oil switch.....the one in the link i posted was nearer to the oil filter

[Stevemorris]

Right, more info...

I have found the 3AW unit, looks like a flasher unit, under the dashboard. I know it should be above the battery and I will maybe get round to moving it back there, eventually/maybe...

So my car has been converted, from a car that should (according to the year) have an oil switch/ignition light set up, to a later car set up (with 3AW relay electronics) fitted.

I may well go back to the oil light set up as additional wires have been added, not too sure as yet, I would like it to be original?

Any thoughts on the following would be appreciated;

1. Should I switch back to the oil light set up?
2. If I leave as is, is the original 'light only on for a brief second when the ignition switched on' problem likely to be the 3AW canister, or the Voltage Regulator (4TR)?

Thanks in advance,

Steve.

[mgcjag]

Hi Steve..is it the 3aw you've found or the indicator relay

[Stevemorris]

Hi Steve, definitely the 3AW. Sat in the car, I switch ignition on, the warning light comes on for about half a second then goes off. If I switch the ignition off, then straight back on, the light won't come on, but if I wait 10-20 seconds then switch the ignition on, it does the same. When I disconnect the 3AW white wire (12V in) it doesn't come on at all. The three terminals on the unit are clearly marked E (earth), AL (alternator) and WL (warning lamp), so it is definitely the 3AW.

It is like something (relay contacts/bi-metal strip) takes 20 odd seconds to reset then it does the same?

I reckon that it's been like it for years (the car has covered around 2000 miles since the full restoration in 1984!) and it was done when the restoration was done by someone who thought it should have the 3AW system on it, and it wasn't supposed to be on there so the alternator isn't compatible?

On later cars the wire AL from the 3AW unit goes to the alternator, which grounds the wire when the alternator isn't spinning, but the ground is switched off when the engine is started, which removes the earth path for the bulb thereby putting the light out. I didn't check it was charging still when I took the power away from the 3AW but I'll wager it is still charging. Tomorrow, I think I will check the AL terminal of the alternator for a ground when not running then no ground when running. If that isn't present then I'll go back to a standard oil switch set up!

Cheers, Steve.