The other night I was at a evening gathering with my wife and daughter. My 1979 300TD failed to start because of a faulty glow plug, (# 5). (The glow plug lamp did not light as well) This I determined by testing the glow plugs with my ohmmeter that I luckily had in my crash kit that I carry in the boot of the wagon. Being quite late and the weather turning to rain I was motivated to to get my family home as quickly as I could rather than leaving the wagon in a parking lot overnight and hailing a cab. The 79 300TD glow plug system is wired in series and if one glow plug goes bad then the whole system is dysfunctional along with the glow panel light. In order to get the glow plugs working again, I decided to rewire the glow plugs wiring harness to by-pass the faulty #5 glow plug. I borrowed a steel coat hanger from the host of the party and fashioned it so as to go from #4 glow plug to the firewall relay/fuse-strip. This worked beautifully, the glow plug indicator lamp came on as normal and the engine started just fine although with a bit more smoke than usual.
So I figured the engine would start and run on four cylinders at first when the engine was cold but I thought that #five cylinder would start to combust and kick in as the engine warmed towards it's normal temp. As I drove home that night the engine ran smooth but a real reduction in power was quite noticeable. So I"m thinking here that #5 cylinder never got lit! (I drove over 20 miles to get home so normal running temp was achieved.) So my question to you all is, why didn't #5 cylinder fire off after the engine warmed up?

Low compression is my guess but the engine has run quite strong up and till this event. I have only 98,000 on the engine! I have yet to install a new plug and haven't driven the wagon since this event the other night!

Any insights or comments?

Thanks...