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View Full Version : headlight/parking light issues- 1970 ambulance


John Zicha
02-09-2018, 04:23 AM
We have our 1970 Cadillac superior ambulance running and driving again. She is quiet, purrs like a kitten and drives very nicely.
When our mechanic shop started working on it, the headlights/market lights etc. all worked. They pulled the engine and trans and replaced it with a known running unit, replaced all the brakes and suspension. Now when you connect the battery (turn on the master switch) the left rear brake light illuminates and so do the rear license plate lights. When you pull out the headlight switch, the dash lights illuminate and so does the right blinker light (constant on), but no lights on the exterior of the car come on at all. I'm thinking there might be a ground wire somewhere that might not be corrected?? I'm trying to figure out where to look first. I also see a button hanging under the dash. I looked it up and its called a brake light switch? I attached a pic of it.
Thanks for any help.

Bill Marcy
02-09-2018, 08:37 AM
Hi John, I will throw a couple of thoughts out, but this is just from my experiences over the years, perhaps somebody who is an expert will have better ideas.
1 Check the dimmer switch, sometimes they go bad, sometimes they have corrosion on them. It sounds odd, but I had a somilar problem with a 68 Cadillac.
2 Check/replace your directional flasher and your four-way flasher boxes, sometimes they cause strange problems with lights.

Let's see some pictures of your ambulance, we love pictures!

John Zicha
02-09-2018, 10:03 AM
The dimmer seems fine. Dims lights on dash. When I push in the brake light switch, the one light that always stays on shus off.

Jacob M. Fournier
02-09-2018, 11:19 AM
1 Check the dimmer switch, sometimes they go bad, sometimes they have corrosion on them. It sounds odd, but I had a somilar problem with a 68 Cadillac.

The dimmer seems fine. Dims lights on dash. When I push in the brake light switch, the one light that always stays on shus off.

Bill wasn't referring to the the dash light dimmer, but the floor mounted switch that dims the headlights (low beam / high beam) - the location of the switch in the floor means that they have a tendency to build up corrosion and cause headlight issues.

The rear brake light is staying on because that brake light switch is loose - it mounts in a bracket up under the dash, close to the base of the brake pedal. When the brake pedal is not being pushed, and the spring returns it to it's normal position, it will push and hold the button in on the brake light switch, keeping the brake lights off - when you step on the brake pedal, the button is released, sending power to the brake lights. As to why only one is on, could be as simple as a bad bulb on the other side, or a wiring issue, or an issue with the directional signal (the directional signals use the same element in the bulb as the brake lights, but have priority over the brake light.)

John ED Renstrom
02-09-2018, 12:26 PM
they left a ground strap of the engine. these late morale ones it's more impotent then ever. if every thing worked before the engine swap it had to be something done during the engine swap. the ground strap is the most likely thing. remember the light bulb doesn't care which way the current flows threw it. so now you know the grounds on that set of light are vary good. a set of jumper cables is all you need to prove it. connect the engine to the neg side of the battery with them and to the body with the other set of clamps. if the problem goes away or changes you know were to look.

John Zicha
02-10-2018, 01:28 AM
Thank you very much. I was thinking a ground of some sort myself. I just didn't know if there were little ground wires that were originally to the engine area that might have been over looked when the new engine was put in.

John Zicha
02-13-2018, 10:28 PM
Yesterday we decided to dive into it a little more. Turned on the headlight switch and...HEADLIGHTS. Out of nowhere. Very Odd. Still no marker lights though. Replaced a couple blown fuses and still nothing. Then I started checking each socket and they are ALL bad. I would never have thought it, but there is power going to each socket, just some are corroded and some are cracked. So now the splicing of new sockets begins.

Paul Steinberg
02-13-2018, 11:40 PM
Before you replace the sockets, disconnect the battery, and clean the sockets with a 1/2" or 3/4" plumbers copper fitting brush. If they clean up great, if not, then replace by soldering in new sockets and wires. Make sure to use shrink tubing over the connections to keep the moisture out. If the sockets clean up, then install new bulbs, and coat each bulb brass end with Vaseline, to keep the moisture out, and corrosion at bay.

John Zicha
02-14-2018, 05:30 AM
We lucked out and 4 of the 6 after cleaning them up worked like a charm!!! The only issue we have now is no lights at all on the passenger side rear lights. I was finally able to gain access by unscrewing and moving a lot of the trim in the back. I was able to find the green and brown wires that go to the lights and there is no power at all going to them. Now we are trying to trace the wires. Since it's an ambulance it looks like the rerouted the wires up into the top of the conversion but not really sure where they come out on the other end in the cab. At least we are getting there little by little.

John ED Renstrom
02-14-2018, 12:46 PM
It is behind the bumper attached to the frame. The connector is about in the center.. Or off to either side. The rear harness usually goes under the carpet threw the tool box threw the wheel well and out rear on the left side.
Same thing with it to clean it. It helps if you use a grease to seal the water out after you clean them. Parts house has that.
But the lights could not have been working before the engine repair.

John Zicha
02-16-2018, 06:06 AM
It is behind the bumper attached to the frame. The connector is about in the center.. Or off to either side. The rear harness usually goes under the carpet threw the tool box threw the wheel well and out rear on the left side.
Same thing with it to clean it. It helps if you use a grease to seal the water out after you clean them. Parts house has that.
But the lights could not have been working before the engine repair.

Unfortunately ours isn't run like that. It goes from the passenger side rear light and staigh up the rear pillar frame into the ceiling.

John ED Renstrom
02-16-2018, 12:23 PM
The plug is still handy. Are you sure that your not looking at the harness that goes to the door switches and the dome light. But no matter what there will be a plug in the rear for each taillight and for each licence plate light.