T-Series Electrical Problem: headlight switch turns starter

[jiml]

Re: Electrical Problem: headlight switch turns sta

yes the part is as you described it and the interval counter is connected.

 

[AlanT]

Re: Electrical Problem: headlight switch turns sta

Anyway the problem should be diagnosed. Either reset the SIC,remove the bulb or replace the diode.

Alan T

 

[Kimberly]

Re: Electrical Problem: headlight switch turns sta

Anyway the problem should be diagnosed. Either reset the SIC,remove the bulb or replace the diode.

Alan T

Alan, please take a look at the wiring diagram and explain to me how the lighting circuit (red and blue wires) are connected to the green/pink or green wires. I have looked at the wiring diagrams and I can't find any point where they are connected.
Jim's complaint is that when he closes the headlight switch (connecting the brown wire to the red/green and blue wires) the starter circuit is energized.

The following is all the wires that get power when the headlight switch is closed if everything is connected correctly; red/green, red/white, red, blue, blue/white, blue/red. For some reason, one of the above wires is supplying power to the starting circuit.

 

[Kimberly]

Re: Electrical Problem: headlight switch turns sta

Jim-

Someone else had a similar problem recently.
https://www.mgexperience.net/phorum/read.php?1,625301

 

[jiml]

Re: Electrical Problem: headlight switch turns sta

after many hours searching out this problem,i focused on the diodes as you suggested.
after removing the service counter diode and hand brake diode, the "headlight start problem" disappeared. the 1976 mgb starts with the ignition switch and the headlight switch works.
so far, i have not been able to find replacement diodes.

many thanks for your help!

jim

 

[Deleted member 3577]

Re: Electrical Problem: headlight switch turns sta

This is just [censored] amusing...

I really love these cars!...
But they sure make you scratch yer head sometimes /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

 

[DrEntropy]

Re: Electrical Problem: headlight switch turns sta

yup. It drove me mad many years back:

Had a headlight switch 'starter' MGB in the shop a number of years ago. IIRC the diodes were acquired at a Radio Shack for the "fix"...

...~after~ a day with a VOM and diagrams. It was so long ago I can't recall just exactly where the feedback runs but do recall it was diode replacement that was the cause/cure. Not certain if it suffered any wiring meltdown issue. Coulda been, that may have fried the diode(s) in the first place. I just can't remember.

 

[Deleted member 3577]

Re: Electrical Problem: headlight switch turns sta

Heard one a few years ago where the car was moving around when no one was looking...
Seems the relay wire was shorting when parked.
Fortunately it was more of a curiosity than dangerous, because it only moved a few feet at a time.
(And never hit anything other than a parking curb)

Wonder who invented the battery switch???

If Lucas didn't...He should at least get credit for sales.

 

[Kimberly]

Re: Electrical Problem: headlight switch turns sta

after many hours searching out this problem,i focused on the diodes as you suggested.
after removing the service counter diode and hand brake diode, the "headlight start problem" disappeared. the 1976 mgb starts with the ignition switch and the headlight switch works.
so far, i have not been able to find replacement diodes.

many thanks for your help!

jim

Don't bother replacing the diodes. Their only function is to provide power to the dash indicator lamps for the service counter and the parking brake when the ignition switch is in the start position, a test feature for the lamps. When they fail, power from the green circuit energizes the white/red wire to the starter relay.