Q – On my 1991 C4 Cab, the intermittent wipers and the “park” function have been inoperative for quite a while. My dash lights have been intermittently inop for a while and now they are completely out as well. So now I can’t drive in the rain and at night, I can’t see my dashboard. Are these problems related? I checked the fuses and they all look good. Electricity mystifies me. Help! Gary
A – You are not alone Gary, electrical problems / gremlins have challenged and annoyed me for over 50 years. One myth that I continue to try and dispel is that you can check a fuse (or a bulb) by looking at it. You might say that is bunk, that you can see a blown fuse or a burnt out bulb my looking at them but I have been fooled dozens of times where I would have been better off walking a few steps over to my box to get my meter.
On the wipers, we begin by checking the fuse for power at both sides of the fuse. Odds are, power is getting to the fuse. (Usually the problem is not on the supply side of the circuit but on the load side.) If the fuse is getting power but the circuit is still dead, remove the fuse and look for signs or heat or burning on the spades of the fuse. Next take a look at the top of the fuse holder in the fuse box to see if it looks charred or melted. (You will need a strong light and a magnifying glass.) If you see evidence of melting, you are onto something. At this point you will want to lift the body of the fuse box up and take a peek under it to see if any other burning or melting is evident underneath where it is hard to see.
The last example of this problem I say involved a melted portion of the fuse panel. The temporary cure is to twist the spades of the fuse so it tensions the loose terminal in the fuse box. The long term cure is to remove the female terminal from the fuse box, replace the terminal, and reinsert it into the box. In a “worst case” you might need to replace the fuse box. There are other more practical, safe and non-factory approved methods of repairing a melted fuse box but if you want to keep it original, this is gonna hurt.
The dash illumination operates through the light switch, fuse box and a computerized relay. One way to check the relay involves twisting it slightly to see if the lights start working. The reason I choose to start at the relay is the intermittent nature of the symptom. When relays start getting flaky, sometimes moving them around will bring them back to life for a while.
In the case of the last failure I was involved in, we popped the cover off the relay, inspected with a magnifying glass and sure enough, found a circuit where the solder had not fully melted into the prong sticking through the circuit board. Odd that it took twenty years to fail. In this situation I recommend a new relay but when you search for one, you discover no one stocks them locally.
So we re-soldered the offending circuit and Bingo! Dash lights!
Intermittent wiper problems and park problems have plagued my own car for years. I have gotten used to parking them manually and frankly, as a short guy, I like them parked on the right side of the windshield rather than the left. I do miss the intermittent feature but you know what they say about “the shoemakers kids going barefoot”. On your Carrera, the intermittent feature (and park) is controlled by another one of those pesky computerized relays and they get flaky with age. Try that twisting trick on the relay and if it works, your choice, replace or fix. – MC