Almost exactly 1 year ago, I bought an aftermarket hood tach for my 68 firebird 350 from The Parts Place on Ebay. The tach worked fine up until a week ago. I first noticed the malfunction right after I washed the car (by hand, not through a carwash). The car has an upgraded HEI on it, so the tach is connected to the distributor through the “tach plug-in” on the distributor. When I turn the ignition on (engine not running), the tach indicator jumps up to about 6000 RPM. When I start the engine, the indicator is all over the place, mostly on zero. While driving, when I back off the accelerator, the needle rises (acts like a vacuum gauge). This morning I noticed that there is condensation behind the lens and there is no response at all in the tach. I drove the car yesterday and it has been sitting in the garage overnight. Any suggestions or ideas?
I guess I wouldn't question the hook up if has worked for almost a year. I would maybe question if water caused an issue.
I thought the Part place tack had a vaccum port to keep moisture out of the tack? As well I thought the lights stayed on all the time to keep the moisture out.
Sounds to me like moisture got in and it now has an internal failure. I'd first contact Parts Place and inquire about any warranty/repair options. If you're lucky they'll hopefully honor it. If you're not you'll probably have to replace it on your dime.
Not sure on their tach but the one I have to just held together with silicone. I know other have been able to cut them apart themselves and work on the inside.
The moisture is probably causing electrical leakage across some of the connections inside the tach .... can try to dry it out in a warm environment eg sit the car in the sun for a couple of hours and it may come good with no damage done.
This was always an issue with the hood tachs. Moisture or condensation, I did notice mine has this problem and it's an after market hood tach, the condensation would go away after the engine heat would cause it to dry out. Mine has operated like this for the 15 yrs and still works today. Last year I found that when I converted from points to electronic ignition that it would work erracticly or not at all, I found that I need to run a new 12v source to the wire that is hooked with the light terminal and it's working again, if moisture is a problem then mine wouldn't work at all, many times it was fogged up. As far as condensation, I maybe wrong but it shouldn't affect it and if you are worried about the moisture they make a kit to keep it dry that was available on 1968 Pontiac's. I have seen it for sale, not sure where though.
I went to a site, Firebird Central just to check out the hood tach vent line, they sell it there. Also they sell the hood tach wire harness and it has 4 plugs on it like it was in the sixties. Does your harness look like that?
Thanks to all for ideas and comments. The HEI was installed before the tach was installed and the dealer said the tach would work with HEI distributors and it did until last week. I drove the car this morning and I don't have the erratic movements, but the needle doesn't move until it should be showing about 2500 RPM. Proportionate response seems to be occurring after that. I contacted The Parts Place this morning but haven't heard anything back as yet.
I have that same tach on my car and it does the same thing after a very wet car wash. I dont get it wet with the hose anymore. Mine cleared up after a few days of drying out.
Good to hear from someone with the same tach and the same problem. It does seem to be clearing up. You wouldn't think that they would be that sensitive to water. God forbid that we should get caught in a downpour while driving! Thanks for the info and taking time to reply.
