Random Electrical Problems 87 Carrera

[Markster]

I bought an 87 Carrera Coupe and am having a number of seemingly random electrical faults. Could these be related or are they each unique? What do you think?

Silent horn (flash Brights), does not work but the brights work with headlight switch on.

No seatbelt buzzer - not that I mind.

Cruise control is inop.

Horns do not work, replaced missing horn contact behind steering wheel, relay is functioning (You can hear it click and I swapped it out for one that I know works) but no horns.

Car is equipped with an alarm system but since I do not have the key cannot test it to know if it works or not.

The Interior lights did not work with the door switches. I pulled the driver's side dome light and found that it must have been shorting out against the body. They now work properly.

[Jeff]

Mark, They seem to be individual problems.

Silent horn... Over time the bright switch contacts can bend out of shape. You need to remove the turn signal switch and bend the contacts (carefully) back into shape. Move the stalk to its different positions and you will figure out where the contacts need to contact. If I remember correctly you will need to pull the steering wheel.

Seat belt buzzer... unless there is a constant draw off your battery I wouldn't worry about it.

Cruise control inop... Could be a disconnected vaccuum hose. LeeH and I fixed his that way. There is also a good step by step trouble shooting guide in the archives.

Horns... Check the other end (where wire connects to the horns) to see if it connected (easy stuff first).

Alarm... Bypass it. I have gone through this and it will leave your car inop. if it gets armed or shorts. I will look for my post on the how to.

[Jeff]

The alarm is located on the left side of the trunk (looking from the front of the car into the trunk). It has an 10 wire harness coming out of it and a relay next to it. The BLUE wire and the BLUE/RED wire are the two #61 terminals.

cut the two #61 wires and connected them together (the ends that lead away from the alarm) and capped off the other ends. I also cut the black wire and connected it with a wire I ran to the bottom of the #8 (rear turn signal/ back-up lights) fuse. Once again this was the end leading away from thealarm unit, and capped off the other end. Started the car and check alternator and voltage regulator function.

You will have to see if your alternator is charging the battery. To do this have a friend hold the RPMs at 1500 and put a mutimeter on the battery (+ to +, - to -) and look for DC voltage between 13.5 and 14.2. If your voltage is between these marks you are charging fine. If it is above 14.2 you may have a faulty voltage regulator.Below not charging.

[Markster]

Thanks. It sounds like each of these items will need to be chased down individually. No common thread unfortunately.

The info about the turn signal contacts is new to me so I will definitely give it a try.

I picked up an inexpensive digital multimeter and I'm going to chase down the horn circuit to find out if I have a bad connection someplace. The Bentley manual talks about pulling the front bumber and fog lights to get at the horns. How accessable are they from below the car? Any ideas?

I am going to abandon the the alarm system and make sure that it is disconnected. I don't need any extra problems.

I'll check the vacuum hoses to make sure the cruise is connected and getting the necessary vacuum.

Do you know if the turn signal switch and the cruise control switch share any common wiring on the steering column?

[Jeff]

You can reach the horns enough to see if the wiring is connected. If you have to replace the horns you will have to follow the Bentley manual and remove the bumper, etc.

If the vaccuum isn't the problem on the cruise, do a search, you will find a good step by step trouble shooting guide directly from the Porsche shop manuals.

The cruise and turn signal don not have common wiring.

Good luck and let us know what you find.

Turn signal stalks go bad all the time. Removing that switch to bend the contacts is a real contortionist act and I never want to do it again. Spring $75 for the new switch and just do this job once. I doubt you'll get it working by bending the contact tabs, since these tend to get fried for lack of relays - also a good idea to install for another $20. Again, do what you can to make the turn signal stalk a one-time-only job.

[curiousone940]

With this many electrical problems, you might take a look at the fuse block for any possible signs of cracking. I had these types of electrical issues with a '76 and finally traced it to fuses that were not making solid contact in the block due to a large crack that could not be seen until the block was removed for inspection. Good luck!!

[aj88cab]

I had just about the same issues when I got my '88 last year. The replies are right on for these (common) items.

The trouble shooting guide for the cruise control is good but first check the brake switch. It is located directly to the right of the gas pedal, inside the center tunnel. There is a lever that extends from the brake peddle shaft that operates the switch. The switch is mounted on a bracket with a screw that can come loose or slip. It needs to be adjusted so the lever just contacts the switch. It should break the switch contact with a small movement of the brake pedal. Use a meter to check. This was the problem with my cruise control. I think I had to remove the floorboard and gas pedal to get to the switch.

I also read somewhere on the board that a burned out brake light (including the center light) can cause cruise control problems but I have never seen that.

Good luck
Andrew