'87 300E Electrical Probs?
 

I hope someone can point me in the right direction. My catalytic converter on my '87 300E recently stopped up to the point that I lost all power. I replaced the cat with a universal cat and replaced the O2 sensor with one out of a '90 Mustang V-8 as I have read here. After installing new components I drove the car approximately 10 miles and the Anti-lock light came on, then lost all power and car stalled. The car acts like the battery is dead. It will jump start, but will only stay running a short time. The battery and alternator are both about a year old. Any thoughts?

You should do a seach on alternators. I am no mecanic but from what I have read on this forum it sounds like that alternator is not fully charging the battery. If you do a search you can find the correct values of cahrge and so forth. Or pull the altonator and ahve it checked at a local car supply store. Could be the voltage regulator....

I would venture a guess that since the problem developed after you did repairs that it is related.
Check what you did, make sure wiring is correct and that you did not 'bump' some connector, or leave something disconnected.

easy alternator check
 

While the car is idling, put a volt meter across the batery terminals, you shoud get 14 volts plus if not then your alternator is bad.

But your problem maybe the OVP relay, unless you made a mistake with the wiring.