voltage drop

ok guys here you go, I have a problem with my charging system. yesterday I found that when my car is "cold" that my output is 13+ volts but as the car warms up it drop to 10+ but as the car cools down it goes back. My readings are from ground to junction "box" and when everything is off it shows the same thing cold high hot low and goes high as it cools down. Now the question is it my cable from the battery to the starter getting hot. my set up is battery to starter sol to junction box and using the "old" big brown wire from the alt to the junction box and all else that needs to be also to the junction box

Just as a knee-jerk reaction, seems that the solid state regulator in the alternator has died. Check the voltage directly at the alternator - should be in the 14.2+ volts or so range. Then trouble shoot the rest of the system, starting with voltage across the battery. Must have clean battery cable clamps and absolute good ground to the frame - the whole electrical system relies on this.

Once you get the voltage up where it needs to be for the computer, maybe the erratic running in your "Vacuum" thread will cure itself.

Wayne

Check Voltage reading at batt car running,,
with alt it should be 14.5 or real close at
double idle speed..
When trouble shooting ANY system always start at one end or the other ,,checks made in sequence
and take notes,,if you jump around it will get
confusing. Best ts tools are eyes and hands.

Sounds to me like a high resistance connection some place. Could be a bad battery for sure. Try a new battery if you have one laying about.

I had a similar problem and it was a shorted battery. It would start the engine, no problem. Also check all of your grounds. You should have one from the battery to the frame (clean, no rust) One from the frame to the engine block and from the frame/frewall to each head. FI systems need the best gorund that you can provide.

Stock MGB wiring weak side is the connections on the passenger side. Those little connectors can create a high resistance. The fix is simple, use new butt connectors or solder the wires together. This will fix many little problems with the elctrical. The connectors I am refering is were the wire looms are put together in the engine bay on the passenger side.
Happy hunting !!!

Make sure that the ground connection from frame/body to engine is good also.
Mine was loose & smoked my choke cable.

Already bought the new connectors, new crimper and will replace all those in the engine comp. Also replaceing all the relays with new one purchased from BMC and rewiring to the terminal box I got from Bill G. I will take the battery out and have it checked out

bingo, had the battery check and it is bad, so i replace it with a group 26 size so maybe santa will leave a 4-link under the tree