Date registered: Nov 2011
Vehicle: 1985 500SL + 2009 GLK (previous 250, 280SL, 230TE, 430 ML)
Location: Oslo, Norway
Mentioned: 2 Post(s)
Quoted: 66 Post(s)
Electronics is a weak point on all old cars, fortunately your 74 SL does not have a lot of it and it is not too complex.
First the indicator flashing, most likely the flasher relay, not expensive and easy to replace.
The ligth circuit needs a bit of trobleshooting, could be several things:
- Bad grounding (usually corrosion)
- Blown/corroded fuses
- Blown bulbs
- Corroded sockets/wire lugs
- Broken wires
- Corroded lightswitch
You will find that a voltmeter is very handy when trouble shooting. It is also possible to troubleshoot with wires.
Grounding can be checked using a wire connect to the chassis at one end touching the ground connector (brown wire), if the bulb then works, you have found the problem.
If grounding is OK, you can connect a long cable to the battery +, connect this wire to the light socket positive, if the bulb lights up, the problem is the wiring, lightswitch or fuse.
You can then connect the cable to the lightswitch output, if the bulbs light up you have a wiring problem. Connect then to the lightswitch input. If the bulb lights up, the switch is the problem.
Be careful not to short the cable connected to battery+, it can easily melt and cause damage to surfaces it touches !
Electrical troubleshooting is not difficult, but requires patience. Make sure you get wiring diagram which shows the wiring colours.