Batboard

Hi guys!

Got a wierd little problem with my 92 Ford Explorer XLT.

I have a 100 Watt A9 VHF Spectra installed witht he Siren/PA Box.

The drawer unit is installed in the rear cargo area on the right hand side up against the rear of the passenger side back seat.

When I key the radio on various channels (and sometimes all of them) the rear window wiper turns itself on and will either run one or two cycles and turn off, or stay on the entire time I have the mic keyed. Once I unkey the mic, the wiper return to park position and stops.

The antenna coax runs under the plastic trim in the cargo area, up the middle of the "C" post to an NMO style mount in the dead center of the roof. I do have a few other antennae on the roof, for cell phone UHF mobile and 2 meter ham.

Anyone have any ideas on what could be causing the rear wiper to be doing this? The only way I can keep it from doing this is to remove the fuse from the fuse panel under the dash.

I am trying to figure this thing out and it is driving me nuts. I have had this vehicle for about 2 years now, and never really had this problem until I uninstalled a 100 watt MaraTrac and replaced it with the high power A( Spectra.

Thanks for your help!

Jeff
Surf City, NC

That would do it.

Different radios will screw with different things. Best bet, try shielding everything as much as possible, and make sure all your RF connections are tight and proper.

VHF tends to be the evil of many vehicles at 100 watts.

If you really don't need a 100watts, reprogram your channels as low power (should get you around 60-70 watts on low) and I bet it will stop. If you really need 100 watts...you will end up relocating the radio or antenna....or trying a different radio altogether.

Check your antenna grounding. That is often the culprit on RFI in vehicles.

This is a common issue with the early and mid-'90s Explorers. VHF range RF makes the rear wipers activate. Just one of those things.

I had a friend with a '92 who was running 50 watts into a VHF mag mount antenna near the rear of the roof. It would activate the wipers every time.

I used to have a '94 with a VHF antenna in the middle of the roof on a well grounded NMO mount. It wouldn't ordinarily activate the rear wiper. However, if the rear gate was open, putting the wiper up in the RF field, it would activate every time.

Pretty funny actually.

well i got a simple fix....pull the fuse.

try a torrid coil on dc and control inputs at the wiper control box

check grounds at radio,antenna mount , and motor .

did you check the swr?



ab

Thanks for all the ideas an info.

I have checked all of the grounds, and rerouted the coax coming from the permanent roof mount and nothis has changed. Everything seems to be good at this point except for that darn rear wiper.

I try something interesting. I disconnected the quick clips that connect the rear window defroster circuit from the vehicle's wiring harness. These are the black plastic clips with the coiled wires at the rear window.

After disconnecting these wires, the rear wiper will only activate with the appropriate switch, and not when I key the radio. Perhaps the defroster strips in the rear window are acting as an antenna and sending stray RF back into the vehicles electrical system somehow.

I checked teh SWR with a Bird 43 watt meter, and everything checks within an acceptable range. I measured 100 watts out and less than 2 reflected on a freq of 153.830, which is the main channel I use for fire operations. I will be disassembling some of my power and ground connections once again, and replacing some of the antenna mounts of coax, along with connectors, just to make sure than any of these aren't the root of the problem.

In the meantime I have pulled the fuse to prevent the rear wiper from activating when I am talking. If I cannot solve the problem from the radio end, perhaps I can install a small relay and a second switch to control the power to the rear wiper, since it is a nice thing to have when it rains and such.

I have noticed that when the rear wiper activates because of the radio, it runs at close to normal speed, but slightly slower, and it attempts to return to the park position when it reaches the end of its cycle, but continues to wipes as usual.

I did notice that I was hearing a slight frowling noise in a UHF maxtrac installed in the same vehicle. I checked the mini-uha ta the back of the maxtrac and it was a little loose, but not to the point of falling off. Perhaps the electrical system is getting some feedback through the power leades of the spectra, or something else along the line.

I am planning on doing some deeper investigating and see what goes from there, and post any findings here.

Thanks again guys!

Jeff
Surf City, NC

Why don't you add a few bypass caps to the electrical wireing. It's amazing what some .01 or .001 caps will do. You can finf the control wiper relay and put the cap on the input. Try to use a good ground and keep the wires short.

You might even try putting a bypass on the rear window connections. It too may resolve the wipper problem.

Jim

scvfd1204 wrote:Hi guys!

Got a wierd little problem with my 92 Ford Explorer XLT.

I have a 100 Watt A9 VHF Spectra installed witht he Siren/PA Box.

The drawer unit is installed in the rear cargo area on the right hand side up against the rear of the passenger side back seat.

When I key the radio on various channels (and sometimes all of them) the rear window wiper turns itself on and will either run one or two cycles and turn off, or stay on the entire time I have the mic keyed. Once I unkey the mic, the wiper return to park position and stops.

Thanks for your help!

Jeff
Surf City, NC

Sorry about the delay.

I am still in the process of investigating the problem and working on solutions as I go along.

I am sure the rear window defogger has something to do with it as well, because if I disconnect the coiled flexible wires on the rear defogger, the problem goes away. Could this possibly mean that I have some cut traces on my rear window defogger?

I'm still working on it, since it is driving me nutz. I have since removed the fuse to the rear wiper, but I still need it from time to time. Oh well, guess I can't have my cake and eat it too.

I will keep this thread updated as I move along and find anything odd or interesting.

Thanks guys!

Jeff
Surf City, NC

i am not so sure that any cut traces in that rear window defogger would have as much to do with it as it is a rather large RF inductor on your vehicle. Chances are...Humhead is dead on.

i can't remember the 92 very well (only had my 95 open once back there)...don't those circuts share some harness space? Follow jim's suggestion and put some caps on those circuts....should help.

Strange, that's a problem I've never encountered in my wife's '94 Explorer. I've got a 100 watt X9000, with siren, mounted behind the trim panel at the right rear of the cargo space, coax routed up the right hand C-post to an NMO in the center of the roof with a Motorola 'Spectra' 5/8 wave antenna. All cabling runs down the right-hand side of the vehicle in the wireway under the door threshold plates. It does also have the rear window defroster. I've never a bit of trouble with the rear wiper, but I do have some trouble with the cruise control. On certain frequencies, with the cruise set, when you just key the radio, nothing happens. When you start talking, the cruise goes haywire. Speed rapidly goes up and down. Perhaps I'm 'modulating' the cruise servo?

As to your problem, I second (or perhaps third? ) the earlier suggestions of toroids on the wiper's power wiring, as well as some bypass caps.