Date registered: May 2011
Vehicle: 1970 Mercedes 250c, 1977 mercedes 230 (put to rest at a junyard she served me well)
Location: Great Barrington, MA
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1970 250c Relay testing
I just bought a 1970 250c, it's in really nice shape, 47,000 miles, 4 spd, everything is nice except a little rust underneath.
It had the carbs swapped to dual webers, and was packed full of speakers and amps which were removed before I bought it. There is definite evidence of monkey-work and improper wiring configuration. The battery terminals also had the red and black reversed, so its possible someone jumped it backwards and fried the electrical system.
It needed an alternator which i already changed, the connector was melted to the back of the old alternator. It also had a bunch of aftermarket gauges that didn't work and when I opened them up I found a bunch of burnt resistors.
The stock water temp and fuel gauge both don't work, the water temp moves a tiny bit sometimes, and my test light got a very faint light at the temperature sensors.
It seems to have two tempurature sensors, I traced these wires (one pink and white, one pink and blue, back to the relay. After testing continuity of the relay and back probing voltage I am starting to suspect the relay is bad.
**Edit: Not sure exactly how this relay works but judging by the diagram printed on the sticker and the results I got, it's not doing what it seems like it should.
***Edit: Also the sticker on it with the diagram says "current on contact 3,5A" but pin 3 and 5 do not contain any connections on the plug.
Does anyone know exactly how to test this relay? It is not your ordinary 4 or 5 pin relay, and when shaken it sounds like stuff is rattling around in there. I have a couple wiring diagrams for this car, but none of them have anything about the water temp circuit, and they don't indicate wire colors.
Help is much appreciated.
Last edited by makinfrenzinmybenz; 04-19-2014 at 04:57 PM.