MGB & GT Forum

I'm a newbie who just purchased a 1970 mgb. It's a dream come true. But this car predates me by almost a decade. I've got a lot to learn.

My speedometer and tachometer are completely unresponsive. The wipers don't work either. I've also seen the ignition warning light shine dimly but that's been inconsistent.

How would you go about diagnosing this?

Get a copy of Rick Ashley's book on MGB electrical systems available at Amazon and a Bentley or Hayes. It will save you hours of frustration.

I think you may have three different problems.

First, the speedometer is a mechanical cable driven from a gear on the back of the transmission. Typically, the interal core of the cable breaks. Remove the cable from the back of the speedometer and pull the core out; you will see immediately if it is broken. You can buy a universal, cut to length replacement but they are getting harder to find. A few months ago I had to go to 5 different auto parts stores before I found one at AutoZone.
http://www.autozone.com/autozone/accessories/Help-125-in-universal-speedometer-cable-kit/_/N-25ip?itemIdentifier=426027_0_0_

When the ignition warning light comes on, it indicates that the alternator voltage is less than the battery voltage. This can mean several different things. It could be that the alternator is bad, the belt is loose or the electrical connections are dirty. Disconnect the electrical connections, clean with CRC Electonic Cleaner (an aerosol found at any parts store), smear with dielectric grease and then re-assemble.

On the tach, most likely it is the electrical connection at the coil. Clean as above. If that doesn't fix it, check the ground that is attached to one of the mounting screws on the back of the tach.

FYI, it is much easier to get to the back of the speedometer by first removing the tach.

---

T. Keith Vezina
British Motoring Club New Orleans
1976 MGB, 1976 MGB Trailer & 1978 MGB V8



Edited 1 time(s). Last edit at 2014-08-20 10:47 AM by Sinewave.

Grounds. Clean and tighten grounds.

Polish all electrical connections to a high luster.

And take a copy of your wiring diagram to a Kinko's and have it blown up to three feet by two feet. Hang on garage wall.

http://advanceautowire.com/mgb.pdf

---

Wayne Sanders
Rose Lodge, OR
(TD 4288)

"I don't care to belong to any club that accepts people like me"-joined Willamette Valley Club in 2011

79/65 MGB - Carmine- V-6 - T-5

This car is now very nearly completely done. Sure to find something else, but not now.........And 12 years later, I'm starting to fix things that were new when we built the car. It's pretty well de-bugged!

Clean all the bullet ends and replace the connectors.
Replace the fuse box.
Call Brad at Autosport Seattle for parts.
Are you anywhere close to Queen Anne or Ballard?

Rob,
What Rick says. Cleaning ALL the connectors and grounds will serve you well.

---

Pogo is right.
—————————————————————-
The power of reasons is an illusion. The belief will not change when the reasons are defeated. The causality is reversed. People believe the reasons because they believe in the conclusion.

Thank you! I'm close enough. I'm on the south end of Beacon Hill.