93 idi with the e40d downshifts when turning headlights on!

CampulanceMan · Dec 15, 2020

The weirdest thing started happening to my converted ambulance last weekend. When the sun went down I turned on the headlights on the highway and immediately the truck downshifted out of overdrive, only the right headlight would turn on and some of the gauges on the instrument cluster would either go all the way down or all the way up. I pulled over and did some inspecting - checked all fuses which were good, changed the headlight bulb that wasn't turning on (it didn't look burned out, but replaced it anyway) and it still doesn't work. Had to just park it and drive home the next day during daylight instead. Anyone have any ideas what could cause this?

cozinsky · Dec 15, 2020

You've got a bad ground somewhere in the headlight circuit.

asmith · Dec 15, 2020

I would agree with a messed up ground but also check your headlight switch too. They like to melt and can cause weird issues. Mine melted and only my headlights would work, nothing else, then as I was driving it switched and only the left side of the truck had lights. new switch fixed it.

theSHERPA · Dec 15, 2020

LED bulbs anywhere in system? Aftermarket headlights?

Sent from my iPhone using Tapatalk

CampulanceMan · Dec 15, 2020

Thanks guys, the truck has LED marker lights and aftermarket projector style headlights. I don't see any obviously exposed/damaged wires under the hood. For the headlight switch - would that be in the dash or under the hood?

MtnHaul · Dec 15, 2020

Pretty sure the switch often malfunctions/melts behind the dash. Actually spoke with someone who had their dash start smoking while they were driving due to a burnt headlight switch.

dan-o · Dec 17, 2020

Hope you and Lefty are doing ok!!!
I would agree that grounds are the first thing to check. My ambulance has a lot of fiberglass that at first glance seems like aluminum. It's not, and makes it hard to find good grounds. I'm going through some wiring nightmares myself. Mostly too many wires to devices I don't need in my ambulance conversion. I disconnect one at a time and see if everything I need still works. It's crude and caveman, I know. But, it's the only way I know to do it without a wiring diagram on a 30 year old ambulance.

BR3 · Dec 19, 2020

The e4od uses the tail light circuit in it's decision making process. Check the tail lights/ground system as well for any issues.

CampulanceMan · Jan 11, 2021

Ok I pulled the headlight switch half expecting it to be mostly a melted plastic mess, but it actually looks really good, at least for it's age. It sounds like I should probably replace it anyway though? Sounds like my next move is to check a bunch of grounds too...I'm such a newby, are there just a few places where all of the wiring harnesses are grounded, or are grounds all over the place? Any diagrams or photos to help a guy understand where to check these grounds? Thanks!

You must be registered for see images attach

CampulanceMan · Jan 11, 2021

Also this video just helped me understand this situation so much better

xc_hide_links_from_guests_guests_error_hide_media

Fredrickson · Jan 11, 2021

@dan-o Have you ever contacted the company that made your box?

I called AEV (who made mine), spoke to a really nice guy, told him the VIN and he sent me a pdf with the entire electrical layout of the truck.. (color of which wire goes where), the whole deal.

Made life so much easier.

93 idi with the e40d downshifts when turning headlights on!

CampulanceMan

Registered User

cozinsky

Full Access Member

asmith

Full Access Member

theSHERPA

Full Access Member

CampulanceMan

Registered User

MtnHaul

Supporting Member

dan-o

Registered User

BR3

Full Access Member

CampulanceMan

Registered User

CampulanceMan

Registered User

Fredrickson

Full Access Member

Similar threads

Latest posts

Forum statistics

Members online

Share this page