Rich9928p

The aftermarket Denon radio in my '87S4 goes off intermittently, and when it comes back on (hours or days later) it forgets all the presets. So, I surmised that the un-switched battery voltage input was the problem. I pulled everything apart to test the voltages.

I found that it has several changes to the stock wiring

- an aftermarket antenna signal booster was installed
- the car previously had a subwoofer installed in the rear

The aftermarket radio has the newer style connector plug installed. The factory plug for power has a larger diameter red wire, a smaller diameter red wire, and a brown wire. The OEM wires are connected in the new style radio connector as follows

Thick OEM red to red (switched 12V) and orange with white strip
Thin OEM red to yellow (un-switched battery)
Brown OEM to black (ground)

The speaker-out wires of the new connector are not connected to the speakers, the RCA amplifier type connectors are used.

Now, my problem. I surmised that the small OEM red wire is the un-switched battery circuit. It didn’t have any voltage. So, I cut the wire and ran another circuit (with an inline fuse) from an un-switched battery source.

I plugged the radio in to the revised wiring, and it turned on! Good first step. But now there is no sound.

My guess is that the booster amp isn’t turned on … I cannot figure any way that by replacing the un-switched circuit would have affected the sound.

- am I correct that the RCA output on radios is for pre-amp out only?

- I can’t find the un-switched battery circuit in the factory wiring diagrams, there must have been a circuit.

There is the possibility that the radio just died, I hope not.

2V4V

Rich,

Sounds like they just used the factory power supply wires to the headunit, and left the rest alone. This is generally a good practice IF it's done well - factory wiring to the speakers usually sucks.

Generally (NOT always) the phono jacks on the back of a head unit are pre-amp out. I don't know Denon stuff well enough to say, but high-end units often have nothing but pre-amp outputs, they have no internal amps.

Thinking that the wire you cut was the power antenna output wire- which is also used in many installs as a 'trigger' wire to turn on your amp(s). No harm as its a "+ to +" scenario, but wouldn't leave it like that.

Quick check would be to meter out that wire as it leaves the radio (not connected to anything else). See if you get +12 with the radio on, but nothing with it off. If that is what you got, then you found the amp switch and the cause of your 'no tunes' condition.

Hard to diag this stuff online, but keep feeding data and I'll try to help.

Trying to remeber what the constant hot is on that circuit, I'll look later. BTW- did you pull up a schematic on the hookups for the headunit itself? This would be most helpful. Probably on the Denon website, or Google it - must be out there somewhere.

Greg

Rich9928p

Today as I was checking wiring again it started to work. As I slid the radio back in and was starting to button up it died again. Either the Denon radio or the amp was bad. So, I decided to install a newer radio that I had from another car. Even though the plug into the radio was the same type, the pin-out was different. It took a little time to splice in the new radio harness.

This new radio has more power per channel (25W) than the origianl S4 booster amp (20W), so I removed the booster amp and ran wires from the radio to the amp speaker out plugs and all is well ... except ... no AM reception. I know that the radio is good so I expect that the antenna or antenna amp is the problem.

I'm not a big AM person anyway, so it isn't a major issue. Though when on a trip I sometimes tune into AM for news and road conditions. Two steps forward, one step back.

Any ideas as to why no AM reception? The radio is a JVC ( Alpine) KS-F150.

2V4V

Rich,

Glad to hear I was miles offbase.

If you have FM, then you *should* have AM. The only way I can see it being an straight antenna issue is if the headunit has a separate AM antenna input (about zero on the likelyhood scale).

The 87 has the windshield antenna, so there may be an issue with the antenna amp if it's not getting power (there'd be enough "antenna" created by the antenna lead to get some FM signal, but not enough wire for AM. Longer wavelength and all that.)

There also may be an antenna "trimming" pot on the unit as well which may require adjustment. Check the owner's manual for the headunit.

Good luck,

Greg

Rich9928p

There is an aftermarket antenna booster installed. So perhaps the original antenna amp was disconnected. The booster does nothing for AM.

I'll dig at that another day. It was 107F today, too warm for Porsche work out in the garage.

Rich9928p

UPDATE: AM reception fixed! One of the PO wiring tracks did have a wire that came from the antenna cable. I plugged this wire into a switched 12V circuit (cigarette lighter) and AM reception came to life.

I think I'm done with PO-based wiring problems. Next fix is an intermittent rear side marker lamp.

2V4V

Rich,

Only 107 in PHX? Gosh, must be a cold wave or something...

Those rear side marker lights are rather exposed to the elements (admittedly the only real 'element' in PHX is "fire" and maybe "earth" but I digress). Anyway, there's a small boot covering the spade connectors to the light unit. I've seen more than a few with boot failure/leakage to corrode those connectors. Also, the bulb receptacle tends to corrode pretty easily. A big can of "De-Oxit" or whatever you like, is most helpful.

Might as well do the seal while you're in there.

Greg

Rich9928p

I took the side marker assembly all apart, cleaned the contacts (they weren't that dirty) and checked the bulb and voltage to the assembly. The bulb was good and no voltage to the wires! Later, the lamp came on. So there is something itermittent "upstream" from the lamp itself.

dr bob

When I added a new head unit in my '89, I decided to eliminate the amp in the pass side box, and wire directly to the speakers from my new high-powered head unit. I sourced some connectors that mate with the original speaker connectors to the amp, and removed the amp. After that, no always-on 12V power to the head unit. Traced the wiring back to a plug where the amp connected. Seems the amp was powered by the car, and the power for the original head unit came from the amp. I sourced a mating connector for where the amp used to go, and just made a jumper to pass the 12V on to the head unit.

Needless to say, the wiring diagrams in the FSM did not accurately represent what was in the car.

When I am that %#@*! PO someday, at least the marked-up wiring diagram taped to the bottom of the head unit will accurately represent what's in the car.


HTH!

JohnBlackWatson

First post and one to express gratitude instead of asking a question.

My UK based GTS was imported from Japan where the radio frequencies are different; choice of stations was limited so went for an upgrade of an old Nakamachi CD400 (seems a popular choice)

After removing the head unit and amp I carefully made up a new harness using the lead from the old unit (not wanting to splice any wires) - unfortunately no permanent feed.

I searched and searched to find out what fuse might have blown and found many different items of advice - finally this thread helped me; made a jumper for the old amp connection and everything works.

Brilliant forum and looking forward to following the dash removal tips when I change the dash-pod to one in MPH.

Many thanks,

John.

morganabowen

Hey Rich,
Good to see you post. Sounds like typical AZ weather. Enjoy it

Landseer

Holy time travel, Batman!

Rich9928p

What a blast from the past. I didn't even remember this thread. The good news, the radio has worked perfectly ever since. A job well done!

dr bob

JohnBlackWatson--

Welcome to the group! And I'm glad the tips helped you. Of course, you are obligated to share pictures of the car from Japan, and maybe some history on how it came to own you.

On your dash display, you can change the displayunits from Metric to Imperial and back using the lower left stalk on the steering column. Pull it and hold it until the units change. That will at least alllow you to display MPH in the left display window if it's showing KPH now. A language change is a lot more complicated.

jthwan22

My radio used to blink off after hitting a bump in the road and come on a little later. Taking it apart I found PO use wire cap to make his power connection. Soldering and shirk tube cure the problem.