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Old 10-06-2003, 05:58 PM
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Join Date: Oct 2003
Location: Ventura CA USA
Posts: 38
560SL newbie - electrical help

Greetings! A beautiful1988 560SL w/ 90K miles is new to me. I have a few electrical problems that I have to sort out, and would appreciate it if someone with MBZ experience checked my logic before I start driving myself nuts because I misunderstand something basic. I’ll do a general once over for loose connections & cracked insulation first.

1. The radio and power antenna do not operate. I have verified that other systems being fed by this fuse are operating (the cigar lighter and the glove box lights). I can pull the head unit (Becker Grand Prix) and bench test it before I mess with the wiring. If it is OK, I’ll trace the hot radio lead to the wiring harness to be sure that the connection is made to a switched hot part of the harness with a VOM. Any idea if these pull power from a common point of the harness? I assume that the radio turning on sends a “up” signal to the antenna, and “down” when turned off, and that the manual antenna switch is wired in parallel with these to allow manual control. If the harness connection point is dead, I’ll pull a new 10A fused line to them from a hot point as supply. Anyone help me with this circuit’s color code???

2. The climate control fan won’t come on. I can hear the a/c clutch engage when I hit any of the push buttons that request a/c, and it disengages when I select economy or off. Hitting the 2 fan positions or automatic produce no air flow out the vents whether requesting hot or cold. The “recirculate” switch appears to not work or not get power. No audible closing / opening of the vents or light coming on. Since I am not hearing any vacuum actuated sounds when selecting different positions, I assume that power isn’t getting that far, or I have a massive vac. leak. Can’t hear any obvious leaks, and the idle is smooth – so I think this is unlikely. Checked other items on that fuse, and they are all working. Heard of another fuse under the hood in one posting – but no clue of location for this one. Color code for circuit? Where is power fed to the push button panel first? And does the recirc. supply come off the panel?

I know electrical problems take time and logical, methodical troubleshooting (I’ve worked on boats for years). Anyone who can help me along?
Many thanks.
Regards, tony
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Old 10-06-2003, 09:10 PM
Gilly's Avatar
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Join Date: Mar 2001
Location: Evansville WI
Posts: 9,616
On the radio, if you can remove it I believe you'll find there is a fuse on the radio chassis itself, as well as the one in the fuse box.
It will be filled with a silica-type material so you'll have to check the fuse with an ohmmeter. Check the rating on the fuse, I believe you'll be able to get one at radio shack, I think it's a 1 amp.
Then, once that's fixed, it'll likely be in "dashed line" mode (display will look like this "= = = = ="). You will need to have a dealer reset the radio with a special tool to get it out of dashed line mode.
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