The Prince of Darness has struck

[GaryBeu]

For the first time (yesterday) I turned on the headlight switch with the car ('71 MGB) running. THE TACH INSTANTLY WENT TO ZERO AND STAYED THERE!! Happens on both switch positions. With the switch off I can flash brights and tach still works. Looking at the wiring diagram, I don't see how this can happen. Wiring doesn't scare me much so I'm sure I'll eventually sort it out but, does anyone have a suggestion that might possibly speed it up? Thanks.

 

[DrEntropy]

Check the entire harness from the lightswitch forward for evidence of previous overheating from a short someplace. Betting there's a "melt" spot somewhere under-dash or where the harness goes forward thru the bulkhead (right front of the engine bay).

 

[GaryBeu]

Hadn't thought of that...we'll check.

 

[JPSmit]

Gary, the notion that some smoke has been let out of your wiring at some point is more than worth following up. It's also worth checking and rechecking your grounds. They can cause some very funky issues! FWIW, the flash brights is a different circuit all together (blue wire instead of purple feeding it) so, it is not surprising that it works while other does not. Good Luck!

 

[rustbucket]

Had the same problem on a friend's MGB. Searching for lose connections, I wiggled the socket for the light on the tach which gave it a better ground. Problem solved. Give it a try.

 

[GaryBeu]

We have it fixed. Searched wiring and found (wrapped up in tape around the harness) under the dash near the steering column some P.O. had ~attempted~to connect some wires with a very NOT good connection. Did it properly and solved the problem. Thanks once again for the advice.

 

[JPSmit]

woo hoo! are you driving now? if so, pics?

 

[GaryBeu]

Still only going on very short test runs. Can't quite get the carbs/timing, etc. right. It's getting much closer though.

 

[mgnewbie]

I am also in the process of waking up my newly acquired 80B and am finding all sorts of nasty stuff after the intial euphoria of getting it stated and driving it around for only a few days...yikes! YB

 

[GaryBeu]

It's pretty daunting. Seems we fix one problem and find another. Had her running smooth yesterday and today she spits and runs ragged again!

 

[DrEntropy]

Old gas? Something pumped from th' dregs and blocking the filter...

 

[JPSmit]

It's pretty daunting. Seems we fix one problem and find another. Had her running smooth yesterday and today she spits and runs ragged again!

pull the plugs again - it may still be too rich

 

[GaryBeu]

Definitely NOT old gas. I'm going to pull the plugs again and check. Sure wish I knew a LOT more about what I'm trying to do :frown:.

 

[JPSmit]

you'll get there I promise - I knew nothing before either