Blown control box ?

[Pascal]

Hi,

I took my Minor for an 80 miles trip last week. The battery was nearly flat (the car had been idle for two months) so I had to crank up the engine manually. Then the ignition light didn't come off.

The car ran ok for about 70 miles but then I turned on the sidelights and it sputtered to a halt after 5 miles.

The next day I recharged the battery and the car started ok but the ignition light is still on. I checked the voltage on the battery terminals with the engine running and it read 12.5 V, which points to no current from control box.

I went to a garage and the guy unplugged terminals A and F (I think) from the control box, connected them together and the ignition light came out, which he said confirmed that the problem was with the control box.

So I have a few questions:

1. Is there a way to fix the defective control box temporarily until I get a new one ?

2. If I can't is it safe to keep using the car like that until it is fixed (with charging the battery every day) ?

3. I fitted halogen headlights two years ago (only drove a few hundred miles since) so I was wondering whether it would be worth swapping the dynamo for an alternator to be on the safe side rather than just replacing the control box ?

Best regards
Pascal

[bmcecosse]

It will be 'safe' to use the car (but don't use anything electrical - heater/lights/wipers) - I'm not at all convinced that the problem is with the control box. Crazy 'test' from that 'garage'.. More likely to be the dynamo brushes - check them first. Constant charging and discharging will soon ruin the battery... Halogen lights use LESS current - so no need for an alternator on that account.

[alexmcguffie]

Take the cover off the regulator and slowly increase engine revs from tickover and watch if the outermost set of contacts closes. If it does then your dynamo is more than likely OK and the regulator contacts may need a clean with emery paper. Don't adjust anything in there though.

Halogen head lights still take 55W like sealed beam headlights so won't have any greater draw on your battery.

[Pascal]

Actually I've tested the dynamo as shown in the workshop manual (wire between the dynamo terminals) and found a reading of less than a volt. I'll try to swap the brushed or swap it with with a reconditioned dynamo altogether.

[Pascal]

By the way given the relatively small price difference between a dynamo and an alternator kit which one would you recommend for peace of mind ?

[bmcecosse]

I see what the garage test may have been - if he powered the F wire from the A connection and RAN THE ENGINE - the light would indeed be out - but did he measure the volts like that? If 13.5/14 volts - then yes, the dynamo is good and the Reg box could be the problem. Real test for the dynamo is to disconnect the wires - join the two terminals with a length of cable - slacken/remove the fan belt - and touch the cable to the non-earth terminal of the battery - the dynamo should run as a motor if it is good. If you have to buy a NEW dynamo - then yes - may as well get an alternator (car must be -ve earth..). But well worth trying (as Alex suggests) cleaning the contacts - and inspecting the brushes. You haven't by any chance reversed the polarity of the car -even 'by accident' taking the battery out and refitting it wrong way round?